Articol TB Treatment 2010

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E u r R e s p ir J 2 0 1 1 ; 3 7 : 4 4 1 - 4 6 2 D O I: 1 0 .1 1 8 3 /0 9 0 3 1 9 3 6 .0 0 0 3 3 0 1 0 C o p y r ig h t© E R S 2 0 1 1

SERIES "UPDATE ON TUBERCULOSIS" Edited by C. Lange, M. Raviglione, W.W. Yew and G.B. Migliori Number 4 in this Series

Treatment of tuberculosis: update 2010
W.W. Yew*, C. Lange# and C.C. Leung*

KEYWORDS Review, tuberculosis, treatment
n 2008, 11.5 million people were estimated to be living with tuberculosis, with 9.4 million of them having incident disease. Among the 1.9 million people who died of tuberculosis, 0.5 million were seropositive for HIV [1]. While the present chemotherapy for tuberculosis is highly efficacious, it has the disadvantages of being lengthy and complex, and does not live up to the expectation of adequately controlling the current global tuberculosis situation. In 2008, an estimated 390,000510,000 cases of multidrugresistant (MDR) tuberculosis with bacillary resistance to at least isoniazid (H) and rifampicin (R) are estimated to emerge every year worldwide, with China and India together accounting for —50% of this global burden. In 2008, MDR tuberculosis caused an estimated

I

emerging extensively drugresistant (XDR) tuberculosis is defined as MDR tuberculosis with additional bacillary resistance to any fluoroquinolone and one or more of the three (second-line) injectable drugs: amikacin, capreomycin and kanamycin. Approximately 5.4% of MDR tuberculosis reported worldwide could be categorised as XDR tuberculosis, with the proportion exceeding 10% in some countries [2]. This article examines the current status and future prospects of treatment of tuberculosis. Where appropriate, evidence levels for the recommended treatment regimens and modalities are given in accordance with the grading system of the Scottish Intercollegiate Guidelines Network (see Appendix) [3]. Before discussing recommended drug regimens for treating of pulmonary tuberculosis, an understanding of basic

tuberculosis drug action would be beneficial.

SCIENTIFIC BASIS OF SHORTCOURSE CHEMOTH ERAPY
Mycobacterium tuberculosis, the causative organism of tuberculosis, is a slow-growing bacterium that can also enter a phase of dormancy, which appears to be drugrefractory. Four hypothetical populations of organisms [4] may exist in a

ABSTRACT: Currently, the standard short-course chemotherapy for tuberculosis comprises a 6-month regimen, with a four-drug intensive phase and a two-drug continuation phase. Alternative chemotherapy using more costly and toxic drugs, often for prolonged durations generally >18 months, is required for multidrug-resistant and extensively drug-resistant tuberculosis. Directly observed treatment, as part of a holistic care programme, is a cost-effective strategy to ensure high treatment success and curtail development of drug resistance in tuberculosis. New antituberculosis drugs are urgently needed to improve the present standard short-course and alternative chemotherapies, by shortening administration durations and increasing cure rates, through the greater potency of these agents. At the same time, the role of adjunctive surgery for drug-resistant tuberculosis has to be better defined. Immunotherapy might improve treatment outcomes of both drug-susceptible and -resistant tuberculosis, and warrants further exploration.

150,000

deaths

[2].

Recently

mycobacteriology

and

anti-

patient

with

tuberculosis: 1) actively growing organisms, usually present in abundance (extracellularly) within aerated cavities; 2) slow, intermittently growing organisms in an unstable part of the lesion; 3) organisms surviving under microaerobic conditions in a low environmental pH, either in inflammatory lesions or within phagolysosomes of macrophages; and 4) completely dormant

organisms surviving anaerobic conditions.
A F F IL IA T IO N S 'T u b e r c u lo s is and Chest

under
G ra n th a m

P a r k a lle e 3 5 B o rs te l 2 3 8 4 5 c la n g e @ fz -

G e rm a n y H -m p ita l, E o s a il: " T u b e r c u lo s is a n d C h e s t S e rv ic e , D e p t o f H e a ltho rs to n g e b , H e l.d U n it, K o n g , C h in a . ^ D iv is io n o f C lin ic a l In fe c tio u s D is e a s e s . e c e te d M e d ic a l C lin ic , R e s e a r c h C e n te r B o rs te l. RB o rsiv el, : G e rm a n y . CO RRESPO N DEN C E C. Lange D iv is io n o f C lin ic a l In fe c tio u s D is e a s e s M e d ic a l C lin ic R e s e a r c h C e n te r B o r s te l M a rc h 0 2 2010 A cc e p te d a ft e r

r e v is io n : M a y 20 2010

Previous articles in this Series: No. 1: E r k e nC G M K a m p h o rs t, A b u b a k a et s , M r I, c o u n ts: i

al. T u b e rc u lo s is

c o n ta c t in v e s tig a tio n in lo w p r e v a le n c e

E u ro p e a n c o n s e nEurResp rJ 2 0 1 0 : 3 6 : 9 2 5 - 9 4 9 . 2: S o lo v ic I, S e s te r M , G o m e z - etal. JJ,h e r is k o f tu b e r c u lo s is r e la te d to tu m o u r sus. No. R e in o T
r n e cc s s ^ r: -

;

I '5 :o ry Jo u r n a l a n ta g o n is t t h e r a p ie s : a T B N E T c o n s e n s u Eurta te m e nJt. 0 1 0 ; 3 6 : 1 1 8 5 - 1 No. .3: S c h u tC , M e in tje s G , A lm a jid F , e / a / . C lin ic a l r s s Respir 2 206 z '
:

; r 1 3 -1 9 3 6 tu b e rc u lo s is a n d H IV - 1 c o - in fe c tio n . J 2 0 1 0 ; 3 6 : 1 4 6 0 - 1 4 8 1 . Eur Respir

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> S S M 3 9 9 -3 0 0 3

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W .W Y E W . ET

The three major actions of antituberculosis drugs [5] are: 1) bactericidal action, defined as their ability to kill actively growing bacilli rapidly, e.g. isoniazid, and to a lesser extent, rifampicin and streptomycin (S); 2) sterilising action, defined as their capacity to kill the semi-dormant organisms, e.g. rifampicin and pyrazinamide (Z); 3) prevention of emergence of bacillary resistance to drugs, e.g. isoniazid and rifampicin; less so for streptomycin, ethambutol (E) and pyrazinamide; least for thiacetazone and ^^-aminosalicylic acid.

with both rifampicin and pyrazinamide should contain 6 months, rather than 2 months, of rifampicin for better efficacv (grade A). A regimen without pvrazinamide in the initial intensive phase must be given for >6 months (grade A). Such a regimen based on isoniazid and rifampicin [13-15] is only good for pansus- ceptible tuberculosis with limited bacillary load, and has to be given for 9 months (namely 2HRE/7HR or 9HR). This 9-month regimen is usually not recommended for patients in countries with high rates of isoniazidresistant tuberculosis, except those who cannot tolerate pyrazinamide. The administration of pyrazinamide beyond 2 months has not been shown to offer any advantage on treatment outcome (grade A) [21, 22]. Also, in cohort and case-control analyses, from ^ 12 weeks after starting treatment, the estimated risk of hepatotoxicity was 2.6% for regimens incorporating pyrazinamide, isoniazid and/or rifampicin and 0.8% for standard regimens containing isoniaizid and rifampicin. Thus, adc pyrazinamide to isoniazid and rifampicin increases the ris] hepatotoxicity appreciably [23]. For individual cases with extensive disease and slow spui bacteriological conversion, administration of pyrazinarr with or without ethambutol beyond 2 months may se acceptable. This prolongation of intensive phase is currently supported by WHO [16]. However, WHO recently raised the possible advantage of using rifampi isoniazid and ethambutol rather than rifampicin and isonia in the continuation phase of treatment of tuberculosis populations with known or suspected high levels of bacill resistance to isoniazid [16]. Initial cavitation and posil sputum culture after 2 months of treatment have been founc be associated with increased risk of failure or relapse, i possibly justify prolongation of the continuation phase antituberculosis therapy to give a total duration of 9 mor [24] (grade B). Intermittent regimens comprising two drugs in the contin tion phase, following an intensive phase of four drugs given a daily basis, have been proven to be highly efficaci< (2HRZS/4H3R3 or 2HRZS/4H2R2) (grade A) [7,10]. WHO d not generally recommend twice-weekly regimens, because the higher risk of treatment failure when missing doses oc [16]. Intermittent short-course regimens administered th times weekly throughout

CHEMOTHERAPY OF PULMONARY TUBERCULOSIS Short-course

chemotherapy regimens

Based on a number of clinical trials performed previously, much knowledge has accumulated regarding chemotherapy regimens for new cases of smear-positive pulmonary tuberculosis [6-15]. The shortest duration of treatment required is, at present, 6 months (grade A). The standard regimen today, as categorically recommended by the World Health Organization (WHO) and International Union Against Tuberculosis and Lung Disease (IUATLD) [16], comprises the combination of HRZE for 2 months, followed by HR for a further 4 months. The aminoglycoside streptomycin is not generally recommended as a fourth drug in the intensive phase, largely because of its higher resistance rate than that of ethambutol [17], and its requirement for the parenteral route of administration. However, in rare occasions when ethambutol use is contraindicated, the streptomycin may be considered. Dosages for the conventional first-line antituberculosis drugs are well established, and can be found in standard references [16, 18]. Although an 8-month regimen consisting of 2 months of SHRZ, followed by 6 months of isoniazid and thiacetazone, combined with hospitalisation in the first 2 months, has previously been shown to be effective in controlled clinical trials and programme settings in Africa [11], a randomised study initiated by IUATLD revealed that the 8month regimen 2HRZE/6HE was significantly inferior to the 6-month regimen 2HRZE/4HR [19]. A systematic review has also shown that regimens utilising rifampicin only for the first 1-2 months had significantly higher rates of failure, relapse and acquired drug resistance compared with regimens that used rifampicin for 6 months [20]. The WHO currently recommends phasing out of the 8month regimen [16]. Thus, short-course antituberculosis chemotherapy regimen

have been shown to have larg equivalent efficacy to daily regimens [8]. A recent nested ca control study raised concerns regarding the efficacy of thr times-weekly 6-month regimens in preventing disease rela] in the presence of cavitation [25]. The systematic revi mentioned earlier [20] did not show any significant differe] in failure or relapse with daily or intermittent scheduling treatment administration, apart from insufficient publisl evidence for the efficacy of twice-weekly rifampicin admir tration throughout therapy. However, major confound: factors, such as cavitation and 2month culture status, mi« be heterogeneous across the included studies and i adequately controlled for in that systematic revk Furthermore, rates of acquired drug resistance among failures 1 and relapses have been shown to be higher with thr times-weekly therapy [20]. Dosing schedules in the fi 9 weeks did not appear to have impact on the risk hepatotoxicity in

another case-control study [26]. Logie regression analysis showed that sex was nonsignificant t ageing increased the odds of hepatitis, the risk of which r( from 2.6% to 4.1% as age exceeded 49 yrs. WHO currently recommends the use of daily dosing duri both the intensive and continuation phase as the most optin approach (table 1). HIV-infected patients who received 6month rifampicinrifabutin-based regimens were shown to have a higher relap rate than those on longer therapy in an early clinical trial and a more recent treatment cohort [28]. Possibly because the poor prognosis associated with the underlying H infection before the availability of antiretroviral therapy, t lower relapse rate did not translate into improved survival the former trial [27]. WHO currently recommends tl tuberculosis patients who are living with HIV should recei

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Daily 3

times per week nes per week 3 times per week YEW ET AL.

SERIES: TUBERCULOSIS

ing frequency: nsive phase

Recommended

Dosing frequency: continuation phase

dosing frequency for standard 6-month

Comments

regimen

east the same duration of treatment as HIV-negative mts. Increased risk of treatment failure and acquired nycin resistance have also been shown to be associated l intermittent regimens among HIV-infected patients 31]. WHO currently recommends that HIV-positive mts with tuberculosis and all tuberculosis patients living IIV-prevalent settings should receive daily treatment, at t during the intensive phase [16]. rtany countries, nearly 50% of patients are diagnosed as Lng active pulmonary tuberculosis on clinical and radio- >hic grounds, without immediate bacteriological confirma- . In the two smear-negative studies conducted in Hong g, China it was found that with 2 and 3 months of daily ^S treatment, the relapse rates were 32% and 13%, •ectively, for culture-positive patients [32], but the rates e much lower with 4month treatment (2% for drug- :eptible tuberculosis and 8% for isoniazid- and ptomycin-resistant tuberculosis) [33]. s, it appears that months of treatment is required for ar-negative pulmonary tuberculosis in non-HIV-infected ents (grade C). WHO currently recommends the use of a onth regimen of daily HRZE for 2 months followed by dailv iree-timesweekly HR for a further 4 months in the treatment ew smear-negative pulmonary tuberculosis patients [16]. relapse rates during the 6-30 months following til standard 6-month shortcourse chemothe

Retreatment drug regimens

For treatment of smear-positive relapse cases of pulmonary tuberculosis, as well as retreatment after interruption, an 8-month regimen has been recommended by WHO and the IUATLD, namely 2HRZES/1HRZE/5HRE (grade D) [16]. With the increasing availability of rapid tests for bacillary drug susceptibilities, such as line probe assays, it would be possible to modify this approach according to the results, particularly in areas with high prevalence of MDR and XDR tuberculosis [16]. Using conventional drug susceptibility testing, it might be necessary to start an empirical retreatment regimen active against MDR disease when the levels of MDR tuberculosis are high in different patient registration groups in the geographical area (grade D). Patients who have failed two rifampicincontaining regimens, the initial and retreatment regimens, are very likely to have MDR tuberculosis. These updated recommendations are now incorporated in the current WHO guidelines (table 2) [16].

Directly observed short-course

treatment,

;.men are erally <5% [6-10]. 78% of relapses occurred within 6 m ?nths topping treatment, and 91% within 12 months

Directly observed treatment (DOT) was shown to be highly efficacious in ensuring patient adherence by experience gained in Chennai (then Madras), India and Hong Kong many decades ago. In 1993, WHO officially announced the new global strategy for tuberculosis control known as directly observed treatment, short-course (DOTS) that implements the 6-month short-course regimen in a programmatic setting z 36J. The DOTS strategy has five key components, which include: 1 a network of trained healthcare or community workers to administer DOT; 2) properly equipped laboratories

previously treated patients Suggested antituberculosis retreatment regimens for
ÍT Likelihood of MDR-TB

utinely available

High rfa ca:e~ts Medium; iov. relapse oefai>: patients) .pid molecular tests DST resufts ava table n 1-2 days to confirm or exclude MDR-

TB to guide treatment regimen used »nventional phenotypic tests results are available)* While awaiting DST -est. "5 2-RZES HRZE'SHRE (to be modified once DST results are available)*
jT: drug susceptibility testing; MDR-TB: multidrug-resistant tuberculosis. stanca'disec individualised regimen if MDR-TB is

While awaiting DST es^'s emp - cal MDR-TB regimen (to be modified once DST

confirmed. Reproduced and modified ■m [16] with permission from the publisher.

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W.W. YEW ET AL.

rained personnel to perform sputum microscopy for tuberculosis; 3) a reliable supply of high-quality preferably at no cost to patients); 4) an accurate record^ and cohort analysis system for monitoring case- g, treatment and outcomes; and 5) sustained political ::ment and funding. An effectively functioning tubercu- ntrol programme is clearly essential for good patient re [36]. Although some patient characteristics, such as .essness, alcohol or substance abuse, behavioural probmental retardation, and lack of social or family support, ore commonly associated with nonadherence to therapy, ften difficult to identify poorly adherent patients because nderlving reasons for such behaviour are not only faceted and complex, but range from characteristics of dividual patients to qualities of the societal and economic rment [37]. Although a Cochrane database systematic concluded that the results of randomised controlled conducted in low-, middle- and high-income countries lot provide assurance that DOT, compared with self- nistered treatment, could impart quantitatively important s on cure or treatment completion in tuberculosis patient the merit of reduction of acquired drug resistance with was not addressed [39]. The DOTS strategy is more than alone: it should be viewed as a comprehensive service, or re^ra! rart thereof, which includes enablers, incentives, 2r or mc r ~:>tk care that are conducive to the success of -eatmer.: rrccramme. In a cluster randomised controlled ~ -arrlrir c the effectiveness of a strategy to improve rrr ;f :: r_:r«erailosis treatment in a resourcepoor setting, niervention package based on improved patient counsel- nd communication, decentralisation of treatment delivery, r: choice of DOT supporter, and reinforcement of super- r activities led to improved patient outcome compared the usual tuberculosis control procedures [40]. In addition od communication skills in healthcare workers, attention e management of the treatment associated side-effects and or nonadherence, and maintaining respect for patient nomy and integrity are of paramount importance [41]. One v has further demonstrated that both familymember and munitv DOTS strategies can attain international targets for ment success under programme conditions [42].

use of fixed-dose combination (FDC) formulations com- xtg two, three or even four drugs may enhance ease of cription for physicians, reduce inadvertent medication r> simplify drug procurement and supply, improve tment adherence by patients, and, thereby, decrease the : development of MDR tuberculosis [43, 44]. In a study c «mpared the levels of acquired drug resistance in er:> who had rifampicin and isoniazid FDC, under self- r ~:~::don settings, the rate was as low as 0.2%, given the r - : the investigation [45]. WHO has included some r'.ets m its list of essential drugs [46]. Only formulations rr c xxl quality should be used [47]. The majority of round no significant difference between FDC tablets fir.^r crags regarding sputum smear conversion rates, inc relapses [48, 49]. However, a Singapore study ; - relapse rates at 2 and 5 yrs of follow-up in ts r. received FDC tablets [50]. Furthermore, FDC 13 canr. i replace treatment supervision completely, as there is still a potential risk of the emergence of drug resistance when these combination tablets are taken irregularly [51].

d-dose formulations

combination

Future possibilities rifamycin use

for

Studies have demonstrated the bactericidal and sterilising activities of rifampicin, as well as their dose and concentration dependence [52-54]. In one study, the maximum dosage of rifampicin tested was 20 mg-kg"1 [53]. Rifampicin at a dosage of >10 mg-kg"1 may also suppress or delay emergence of resistance [54]. Early chemotherapy trials that evaluated the use of high-dose rifampicin have shown better 1- or 2-month bacteriological conversion but not a more favourable relapse rate, probably due to absence of the inclusion of pyrazinamide in the treatment regimens [55]. The safety and tolerability of high-dose rifampicin were not meticulously assessed in the early chemotherapy trials, leaving potential concern over these issues. Although rifampicin hepatotoxicity was thought to be idiosyncratic in nature [56], it is not possible to exclude interactive toxicity between isoniazid and rifampicin [57]. Thus, it may not be entirely appropriate to extrapolate safety data from the use of highdose rifampicin in treatment of other bacterial infections, such as brucellosis [55]. In fact, mild hepatotoxicity occurred more frequently in a study among patients who received high-dose rifampicin for tuberculosis treatment, although no patient

developed serious hepatotoxicity [58]. "Flu-like" syndrome has also been associated with high-dose rifampicin, but mainly for intermittent rifampicin administration, and it generally occurs after 3 months of drug administration [59]. Thrombocytopenia, haemolytic anaemia and acute renal failure may also occur. Since these reactions are immunological in origin, they are not likely to occur more frequently when a higher dosage of rifampicin is used [59]. Further clinical trials would be needed to examine whether such a strategy could enhance bacillary sterilisation and shorten tuberculosis therapy without excessive adverse effects [60]. A phase II clinical trial is being conducted to compare the pharmacokinetics and pharmacodynamics of daily doses of 900 and 1,200 mg rifampicin with the standard 600-mg dose during the 2month intensive phase of treatment [61]. Early trials of rifapentine, a long-acting cyclopentyl rifamycin with a plasma halflife of 14 h, given in a 600-mg dose

together with isoniazid on a once-weekly basis during the continuation phase of treatment in patients with tuberculosis have shown satisfactory efficacy in a subgroup of HIV-negative patients with noncavitary disease and limited bacterial burden, despite an overall failure/relapse rate of 10% [62, 63], and emergence of rifamycin monoresistance in relapse cases among HIVpositive subjects [29]. It has been shown that a 900-mg dose of rifapentine had superior pharmacokinetics to the 600-mg dose [64, 65], and that a 1,200-mg dose of rifapentine produced an optimum pulse and postantibiotic lag on the growth of M. tuberculosis [52]. In a murine model, twiceweekly regimens containing rifapentine (1520 mg-kg"1) have shown marked antituberculosis potency by enhancing the rifamycin exposure [66] and preliminary data using daily dosing of rifapentine have also been encouraging [67]. Rifapentine autoinduction of metabolism has also been noted with interest [68]. Currently, there are only sufficient data on the safety and good tolerance of rifapentine dosed at 900 mg once-weekly [69]. However, in

volume 37 number EUROPEAN RESPIRATORY JOURNAL 2

W.W. YEW ET AL. S E R IE STUBERCULOSIS :

an ongoing phase II clinical trial, rifapentine dosed at 10 mg-kg"1 5 days-week"1 is being administered [70], and no unusual preponderance of adverse events was reported by the Data and Safety Monitoring Committee so far.

CHEMOTHERAPY OF PULMONARY MDR AND XDR TUBERCULOSIS
The clinical relevance of antituberculosis drug resistance will be reviewed first as a background to the treatment of drugresistant tuberculosis, especially the MDR and XDR forms.

after 2 months, the relapse rate after 6 months of treatment rises to 10% [22]. As there may be a genuine chance of resistance amplification with additional resistance to rifampicin [20, 72] (especially for HIV status and/or intermittent dosing [20, 28, 31]) some authorities recommend changing to alternative regimens, such as REZ or RE, for more prolonged durations of administration, often yr (grade D) [73, 74]. Currently, the most optimal regimen for treatment of isoniazid-resistant tuberculosis appears unknown [16]. Rifampicin-resistant tuberculosis carries a much more ominous prognosis, as the outcome of standard short-course regimens for such disease is poor, in terms of both disease status on cessation of treatment and subsequent relapse [75]. A recommendation has been made to treat such disease with EHZ for 18-24 months (grade D) [76]. Some authorities feel that the duration of treatment can be shortened to 12 months by the addition of a fluoroquinolone to this three-drug regimen (grade D) [24]. Furthermore, rifampicin monoresistance in M. tuberculosis is usually rare, except perhaps in HIV-infected patients [28, 31, 76, 77]. Thus, rifampicin resistance generally serves as a surrogate marker for dual resistance to rifampicin and isoniazid, i.e. MDR tuberculosis [78, 79], especially for previously treated patients. Shortcourse chemotherapy can cure <60% of MDR tuberculosis cases [80], with a high recurrence rate of ~28:o among those with apparent success [81]. A recent analysis has shown that the currently recommended short-course treatment regimens for both initial and retreatment purposes could not achieve good outcome- - failures, relapses and deaths) in countries having initial rates >3% [82]. It is quite clear today that alternative specific chemotherapy using second-line management of this formidable conditic r ^ : Increased risk for development of bac:liar. ~: ethambutol and pyrazinamide likely occ ; four-drug regimen for initial treatment and a drug retreatment regimen are repeatedly administer :: j-^r.:. observed treatment failure with the conventional sr. .--e regimens for tuberculosis [84-86]. Pyrazinamide and or etr rr- butol resistance, in addition to dual resistance to isoniazid and rifampicin, generally portends a more adverse prognosis in MDR tuberculosis [87], particularly when patients receive on]. standardised second-

Clinical relevance antituberculosis resistance

of drug

Resistance to an antituberculosis drugs arises spontaneously through chromosomal mutation at a frequency of 10~6-10~8 bacterial replications [36]. The chromosomal loci involved are distinct for the major classes of drugs. Thus, when three or more effective drugs are used in combination, spontaneous emergence of mutants resistant to all drugs is most unlikely with the usual bacterial load in the diseased host. However, sequential genetic mutations may be amplified through human error, resulting in clinically drugresistant tuberculosis. These include "monotherapy" due to irregular drug supply, inappropriate doctor prescription and poor patient adherence to treatment [36]. Subsequent transmission of resistant M. tuberculosis strains from the index patient to others, as facilitated by diagnostic delay and infection-control breach, aggravates the problem [71]. A recent review regarding epidemiology of MDR tuberculosis showed that the risk factors for drug resistance pertain to those facilitating the selection of resistance in the community and the specific conditions that appear to increase the vulnerability of some patients, such as in certain HIV or malabsorption settings. The epidemiological situation is principally related to poor treatment practices and poor implementation of control programmes [71]. Isoniazid resistance is the most common form of drug resistance encountered, whether in isolation or in combination with other drugs [2]. Standard short-course chemotherapy for isoniazid-resistant tuberculosis can achieve good success (>95% cure rate) when all four drugs are used throughout the 6 months of treatment (grade B) [21]. When the four drugs are reduced to only rifampicin and isoniazid

line antituberculosis drug regimens with pyrazinamide and ethambutol plus a fluoroquinolone and aminoglycoside or capreomycin. Fluoroquinolones are generally regarded as having a pivotal role in the treatment of MDR tuberculosis [88-90]. In : : resistance to fluoroquinolones has been shown to predict a poor outcome in the treatment of MDR tuberculosis [88,91, 92 Most fluoroquinolone resistance in M. tuberculosis is associated with the injudicious use of this class of drugs in the management of tuberculosis, particularly MDR tuberculosis [93, 94" including the use of suboptimal second-line drug regimens comprising an inadequate number, dosage and/or quality o: accompanying agents [84]. Overzealous use of this class of antimicrobials in the treatment of lower respiratory tract and other communityacquired infections might also contribute to development of fluoroquinolone-resistant tuberculosis [95]. As the aminoglycosides and capreomycin have potent antituberculosis activity, the loss of these second-line injectables together with fluoroquinolones, through
EUROPEAN RESPIRATORY JOURNAL

their suboptimal us«r in the management of MDR tuberculosis would result in XDR tuberculosis, which, in general, carries a worse prognosis

Programme strategies and implementation

The emergence of drug resistance in M. tuberculosa h^s prompted WHO to modify the DOTS strategy to a rr comprehensive approach, the Stop TB strategy [97] Tr strategy comprises the following components: 1) pursu:: high-quality DOTS expansion and enhancement; 21 addre — _ tuberculosis in HIV patients, MDR tubercuosis and the r — s * poor and vulnerable populations; 3) contribution :: system strengthening based on primary healthcare : - _ _ _ all care providers; 5) empowering people with tuberc- sis ; : * and communities through partnership; and 6 enar „:: : - : promoting research. The management of MDR -s through the use of alternative second-line anr.7„ r - - : _ chemotherapy mandates its delivery on a pro^rarrjr i

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with five key components built on the DOTS framework (fig. 1). The capacity for performing drug susceptibility testing and availability of second-line drugs are not adequate to achieve cure. Other factors, such as a set of standard procedures, clear guidelines on treatment and follow-up of patients and administration of DOT, must be included in the programme for MDR tuberculosis management to attain good results [83]. There are basically three possible programmatic approaches for the management of MDR tuberculosis [83]: 1) standardised treatment, in which regimens are designed on the basis of representative drug-resistance surveillance data of specific treatment categories, with all patients in the same group or category being treated by the same regimen; 2) empirical treatment, in which each patient's regimen is individually designed on the basis of the previous history of antituberculosis therapy with the help of representative drugresistance surveillance data, followed by regimen adjustment when the individual drug susceptibility testing results are known; 3) individualised treatment, in which each patient's regimen is designed on the basis of previous history of antituberculosis treatment and individual drug susceptibility testing results. While a standardised regimen enables simple operation and broadens access to care, there may be concern over the amplification of multidrug resistance if the number of available second-line drugs in the regimen is low [98, 99]. Individualised treatment strategies rely heavily on capable laboratory services, but have the advantage of avoiding placing patients on toxic and expensive drugs to which the M. tuberculosis strain is resistant. One caveat, however, is the unsatisfactory reliability of second-line drug susceptibility testing results for many agents aside from the fluoroquinolones and the injectables,

arising partly from the difficulty in standardising testing methodology [100102]. However, some progress has been made accordingly [103]. Patients who had previous treatment with second-line drugs would probably benefit more from the administration of individualised regi mens. When re-treated patients are presumed to have a higl likelihood of MDR tuberculosis, an empirical regimen can b( administered while awaiting the results of conventional dru£ susceptibility testing [16]. Regardless of the strategy advocated, there are significant cos! issues in the management of MDR tuberculosis patients [104]. In a previous decision analysis, it was shown that more patients would die from tuberculosis if the implementation of a drug resistance programme is associated with even minimal decreases in the effectiveness of DOTS [105]. Nevertheless, the feasibility and cost-effectiveness of treatment of MDR tuberculosis is now quite well established, even in resource-limited settings [106, 107]. In countries with significant financial difficulties, additional support, besides technical assistance, from international organisations and governments of industrialised countries would be needed, further to that obtained from local governments [108]. In this regard, the Green Light Committee of the Stop TB Partnership, involving WHO and collaborators, has played a significant role in helping the implementation of these programmes in countries with an affordability problem in the management of MDR tuberculosis [109].

Design of drug regimens

Guidelines on the treatment of MDR tuberculosis are often formulated based on experience and observational studies, as data from randomised trials are lacking. A detailed review has addressed the evidence and controversy of treatment of MDR tuberculosis, focusing on the number of antituberculosis drugs required to treat MDR tuberculosis, the most rational use of effective drugs against the disease, the advisable length of parenteral drug administration or of the initial phase of therapy, the contribution of surgery to the management of MDR tuberculosis, and the optimal approach for treating MDR disease (standardised versus individualised regimens). However, little evidence, but much controversy, was found regarding the the treatment of MDR tuberculosis [110]. Randomised

Rational case-finding Standardised / Appropriate treatment \ strategy: qualityrecording second-line strategies using and FIGURE 1. Directly and of treatment, antituberculosis drugsframework short-course system for Uninterrupted supply Sustained assured culture observed reporting (DOTS) under applied drug susceptibility of drug-resistant tuberculosis. Reproduced X to the management political proper drug-resistant case management and quality-assured second-line modified from [83] with permission from the publisher. antituberculosis drugscommitment conditions / testing tuberculosis control

controlled trials regarding chemotherapy of MDR tuberculosis should be undertaken to provide more evidence-based recommendations [111]. The updated WHO guidelines in 2008 and 2009 recommend designing treatment regimens with a consistent approach based on the hierarchy of five categories of antituberculosis drugs (table 3) [16,112]. The potency of these drugs is in a descending order; thus, the drugs are selected from these five groups accordingly. A brief review of the utility of these drugs is detailed below. While isoniazid in conventional doses has limited usefulness, high-dose isoniazid (>10 mg-kg"1) has demonstrated some

efficacy (clinical, bacteriological and radiographic) as well as reasonable patient tolerance in a recent study [113]. After adjustment for potential confounders, subjects who received high-dose isoniazid had a 2.37-fold higher likelihood of becoming culture-negative at 6 months. Isoniazid-resistant M. tuberculosis organisms belonging to the low-resistance phenotype often have cross-resistance to ethionamide, while those of the highresistance phenotype are more susceptible. Adding high-dose isoniazid kills the former, leaving the latter that are more susceptible to the ethionamide included in the MDR tuberculosis regimen. Ethambutol and pyrazinamide

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iylJ^jKjl Categori es of antitube rculosis drugs
Category 1: firstline oral drugs

2 : f l u o r o q u i n o l o n e s

I s o n i a z i d R i f a m p i c i n E t h a m b u t o l P y r a z i n a m i d e
C a t e g o r y

L e v o f l o x a c i n M o x i f l o x a c i n O f l o x a c i n
C a t e g

o r y 3 : i n j e c t a b l e a g e n t s

n
Category 4: oral bacteriost atic secondline agents

E t h i o n a m i d e P r o t h i o n a m i d e

C a p r e o m y c i n A m i k a c i n K a n a m y c i n S t r e p t o m y c i

P a r a a i n o s a l i c y l i c a c i d C y c l o s e r m

i n e Terizidon e
Categor y 5: agents with efficacy that is not totally clear (not generall y ecomme nded by WHO for routine use in treating patients with rugresistan t tubercul osis)

aid be include d in the treatm ent regime n if they are likely e effectiv e from laborat ory eviden ce or clinical history. »roqui nolone (Categ ory 2) therap y is indepe ndentl y asso'd with better treatm ent outco mes. Losing this drug ^ory increas es risk of death and failure [89, 114]. Thus, a 'oquino lone should be include d whene ver possibl e, >ugh potenti al crossresista nce among the class

Isoniazid (highdose; >10 mgkg"1) Linezolid Amoxicilli nclavulana te Clarithro mycin Clofazimi ne Meropen em plus clavulana te Thiacetaz one Rifabutin HO: World Health Organizat ion. Reprodue d and modified from [16] with rmission from the publisher.

memb ers hampe r their utility in XDR tuberc ulosis [115]. Older oquino lones, especi ally ciprofl oxacin, are not recomled, as there could be a slower sputu m culture conver sion a higher relaps e rate [116]. Newer fluoroq uinolo nes, floxaci n and levoflo xacin, can be active agains t some acinresista nt strains of M. tuberc ulosis [117, 118]. the high rate of stre pto myci n resis tanc e amo ng

MDR ary strai ns, an injec table agen t from Cate gory 3, amik acin, omy cin or kana myci n, shoul d form part of the regi men, as possi ble. Capr eom ycin may have a furth er adva ntag e, 5 to its inco mple te cross resis tanc e with kana mvci n and icin in som e M. tube rculo sis strai ns

[119 , 120] . How ever, >le cros sresis tanc e exist s amo ng thes e thre e seco ndline ibles . Injec table agen ts are gene rally reco mme nded for ^6 months, or 4 months after culture conversi on, with modifica tion accordin g to bacillary resistanc e or patient intoleran ce [83]. Category 4 agents are generall y less efficacio us and more difficult to tolerate. Cycloseri

ne/terizi done have potential ly serious neurotox icity. The use of thioamid es and paraaminosal icylic acid are notoriou sly associat ed with gastrointestinal reactions and other adverse events [83,117]. They are added accordin g to estimate d bacillary suscepti bility, drug history, efficacy, sideeffect profile and cost. Category 5 drugs, including linezolid, amoxicill inclavulan ate, meropen em/clavu lanate and clofazimi ne, are not generally recomm ended in drugresistant tubercul osis, because

their roles are uncertai n [112]. However , they have potential role in situation s without other options, especiall y in patients with XDR tubercul osis [16, 121]. Clinical experien ce on linezolid has been slowly accumul ating after the first report of its good in vitro activities against M. tubercul osis a decade ago [122]. In one study, nine out of 10 MDR tubercul osis patients given linezolid and other drugs in a DOT setting were cured, despite substant ial haemato logical

and neurolog ical toxicities [123]. Use of linezolid at half dose (600 mgday"1) helped to reduce bone marrow suppress ion, but not peripher al and optic neuropat hy [124]. Fatal lactic acidosis can also occur after prolonge d therapy [125]. A sizeable retrospe ctive study has confirme d these adverse effects [126]. Most of them occurred after 60 days of therapy [126]. More major sideeffects occurred with twicedaily than oncedaily dosing, with no differenc e in

efficacy. Outcome s were similar in patients treated with or without linezolid, although linezolid use was assocate d with more extensiv e resistanc e to firstand secondline drugs. Thus, it appears that linezolid (600 mg oncedaily), when added to an individu alised multidru g regimen, may improve bacteriol ogical conversion and treatme nt success in the most complica ted MDR or XDR tubercul osis cases [126]. Its use might not be warrante d where better tolerated alternati ves are

available . Further evaluatio n of linezolid at a dose of 600 mg-day"1 is being conducte d in a phase I/II clinical trial in South Africa [127]. Linezolid (300 mgday"1), in addition to good toleranc e, appeare d to have reasonab le efficacy in a recent study [128]. However , concerns have been raised regardin g the method of analysis and possible emergen ce of drug resistanc e [129]. Another oxazolidi none, PNU100480, has demonst rated more potent activity in vitro and in a murine

model [130], while AZD584 7 is undergoi ng phase I trial in healthy voluntee rs [131]. Amoxicill inclavulan ate has some early bacterici dal effect against M. tubercul osis [132] and distinct inhibitor y activity on MDR strains [133]. Other plactamplactamas e inhibitor combina tions have also shown similar in vitro activity [134], but clinical efficacy data are limited [135, 136]. Imipene

m/ cilastatin is active against MDR and XDR strains M. tubercul osis in vitro [137]. There are also some limited efficacy data of imipene m in mice and humans [138]. When meropen em, a carbape nem (a newer congene r of imipene m), was combine d with the (3lactamas e inhibitor clavulan ate, potent activity against laborator y strains of M. tubercul osis was observed , with sterilisati on of aerobical lv grown cultures achieved within

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14 days [139]. In addition, this combina tion exhibite d activity against anaerobi cally grown cultures that mimic the mycoba cterial persister s, and inhibited the growth of 13 XDR strains of M. tubercul osis at the same levels as observe d for drugsuscepti ble strains [139]. Thus, meropen emclavulan ate might have a potential role in the treatme nt of tubercul osis [140]. Clofazim ine, a riminoph enazine, and some of

its analogu es, have been shown to possess in vitro and in vivo activities against M. tubercul osis, including drugresistant strains [141, 142]. Clofazim ine is primarily used in the treatme nt of leprosy but is sometim es incorpor ated in the treatme nt regimen s for MDR tubercul osis, although data on its clinical efficacy [143] and toleranc e [144] are limited and conflictin g. Rifabutin has very limited potential utility in treatme

nt of MDR tubercul osis due to its high crossresistanc e rate with rifampici n [16]. MDR and XDR tubercul osis should be treated aggressi vely. The fluoroqui nolones and injectabl es are the most potent secondline agents for MDR tubercul osis (grade C). In the initial 6 months, the treatme nt regimen should consist of at least four noncross -reacting drugs to which the organis m is, or is likely to be, suscepti ble (grade C). Generall y speaking , those patients

who have previousl y received secondline drugs are more likely to need a higher number of drugs, as do patients with more extensiv e radiogra phic disease and more formidable drug resistanc e patterns. The use of capreom ycin/ kanamyc in/amika cin, fluoroqui nolone, ethambu tol, pyrazina mide and ethiona mide/pro thionami de for disease with bacillary resistanc e to RH (with or without S), and the use of capreom ycin/kan amycin/a mikacin, fluoroqui nolone,

ethionamide /prothion amide, cycloseri ne and jPtfraaminosal icylic acid for disease with bacillary resistanc e to RHEZ (with or without S) constitut e importan t example s of these regimen s. The possibilit y of further acquired resistanc e should be consider ed. A single drug should never be added to a failing regimen, for fear of selecting mutants that are resistant to the newly added drug (addition phenom enon) [84]. Care is also warrante d in chemoth erapy trials involving

newly develop ed antitube rculosis drugs. Linezolid resistanc e among M. tubercul osis is fairly well known today, and may serve as a warning [145, 146]. The dosages of secondline drugs used in the treatme nt of MDR and XDR tubercul osis are listed in table 4 [83, 112, 147]. The maximu m dosage of cycloseri ne and ethiona mide/ prothion amide should generall y be 750 mg when oncedaily dosing is used, as there is concern over toxicity for higher

doses. The same likely applies also for aminogl ycosides / capreom ycin given three to five times per week [147]. Some of the patients weighing >70 kg might tolerate 1,000 mg for these three classes of drugs [112]. The maximu m oncedaily dosage of moxiflox acin and levofloxa cin is 400 mg and 750800 mg, respecti vely. While the efficacy of 1,000 mg levofloxa cin per day is high [148], the toleranc e data are still limited. WHO recomm ends a treatme

nt duration of ^ 18 months after culture conversi on, even for HIVnegative patients (grade D) [83]. However , a proporti on of immuno compete nt patients who manage d to achieve sustaine d sputum culture conversi on early might be adequat ely treated with 12 months of fluoroqui nolonecontaini ng regimen s [88,149] . It appears, however , that patients who are immuno compro mised (includin g those with diabetes mellitus and silicosis), or have extensiv e radiogra phic

evidence of disease (particul arly with cavities), extensiv e drug resistanc e, delayed sputum culture conversi on (i.e. after >3 months of chemoth erapy) or extrapul monary involvem ent should receive >12 months of therapy [88]. Another importan t principle in the chemoth erapy of MDR and XDR tubercul osis is to exercise vigilance to prevent and manage adverse reaction s. Secondline drugs for treating MDR tubercul osis are generall y more toxic and difficult to

tolerate. In a study on MDR tubercul osis in Hong Kong, — 40% of the patients experien ced adverse drug reaction s of varying severity [88]. However , only half of the patients required modifica tion of their drug regimen s. These results corrobor ated the findings of a study of MDR tubercul osis patients in Peru, where the adverse drug reaction s never resulted in discontin uation of antitube rculosis therapy and only occasion ally (11.7%) resulted in suspensi on of an agent [150]. In

a reported series of MDR tubercul osis patients in Turkey, —70% of the patients experien ced adverse effects to the secondline agents and 55.5% required treatme nt modifica tion [151]. With timely and appropri ate manage ment, the treatme nt success rate (77.6%) did not appear to be markedl y compro mised. Indeed, the results from Turkey largely parallele d those pooled from five sites (Estonia, Latvia, Peru, The Philippin es and Russia)

in resource -limited settings [107]. The secondline antitube rculosis drugs are handled in patients by different pathway s, including diverse metaboli c ones. There is a potential for their interacti on with different classes of antiretro viral drugs [152]. Close clinical monitori ng is necessar y to ensure that adverse drug effects are recognis ed quickly. Apart from clinical monitori ng, ancillary investiga tions, such as audiome try screenin g, vestibula

r assessm ent and biochemi cal tests, including those of liver and renal function s, electroly tes, and thyroid function s, are helpful. In addition to assessm ent of visual acuity, tests to detect peripher al neuropat hy are occasion ally needed. The optimal intervals at which these investiga tions should be perform ed are unknown . Physicia ns should be aware that some of the adverse effects that can occur during the continua tion phase of an extende

d course of antitube rculosis therapy can emerge within a few days. When an adverse reaction is mild and not dangero us, such as a gastroint estinal one, continua tion of therapy alongsid e supporti ve treatme nt is sufficien t. If an adverse event is severe or potential ly dangero us, such as a neurolog ical effect, a more intensive manage ment strategy embraci ng supporti ve treatme nt and drug discontin uation or dosage adjustm ent is required [83]. Psychos ocial

support is also an importan t element in the manage ment of adverse reaction s. Educatio n, counselli ng and encoura gement can all contribut e to a successf ul outcome [83]. Patients developi ng nephroto xicity were found to have a significa ntly longer duration

of treatme nt with aminogl ycosides and received a higher total dose. Predispo sing factors for ototoxici ty of aminogl ycosides are less well characte rised, except perhaps for old age, renal impairm ent and prolonge d therapy [153]. Ototoxici ty due to aminogl ycosides can be

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Dosages of antituberculosis drugs used in treatment of multidrug-resistant tuberculosis in adults
Daily dosage#

Usual daily do

Drug TABLE

4

A m S

t P

a C
l A 5 0 7 5 0 '

m 7

1 7 5 0
r

5 1 5 1 5 15

7 5 0 "
6 0 0 8 0 0
c

1 5 1 5 1 5 20 30 15 15 20 0 2. 5

5 0 0 7 5 0 *
H

4 0 0 *
;

5

0 0 -

#

: drugs are generally given on daily basis except for

a

aminoglycosides and the allied injectable antibiotics, which are given three to five times per week, the as well as those dosage otherwise specified; * : usually maximum daily (some of the patients weighing >70 kg can tolerate higher dosages: see main text); higher dosage usually given for fluoroquinolone-resistant disease; §: optimal dosage not fully delineated;f: may require administration doses per in day; two split requires

administration in split doses per day; should only be used in patients documented to be HIVnegative, and usually not be chosen drugs;
++

over

other

oral

bacteriostatic fully confirmed.

second-line

: long-term safety not

irreversi ble and patients need to be counselle d to report symptom s at the earliest signs of occurren ce.

Treat ment outco mes

Treatme nt outcome s of MDR and XDR tuberculo sis vary greatly between studies [88-90, 92, 154167], possibly related to

variation s in method of analysis, definition of treatmen t success and failure, drug suscepti bility testing, clinical followup, and missing data. The outcome s also likely depend on adverse events due to drugs and their manage ment, as well as supply and

availabili ty of the agents for treatmen t. For MDR tuberculo sis, success rates (cures and treatmen t completi ons) are around 50-70% [88-90. 92 154167]. In a recent systemat ic review [168], the MDR tuberculo sis treatment success rate improved with treatmen t duration of ^18 months and DOT througho ut treatmen t. Studies that combine d both factors had significa ntly higher pooled success rate than other studies (69 versus 58°o). Individua lised treatmen t regimens conferre d a

higher success rate (64°o) than standardi sed regimens (54%), although the differenc e was not statistica lly significan t. In general, patients with XDR tuberculosis had worse treatmen t success rates (^50%) [164166], although one study has shown a remarka ble treatmen t success rate of 60.4%, which is compara ble with that (66.3%) of MDR tuberculo sis in the same locality [169]. Prior antituber culosis therapy [89, 90, 92, 154, 157, 167], extensiv e in vitro drug resistanc e [87, 89, 92,

157, 165], fluoroqui nolone resistanc e [88, 90, 92, 158, 167] or prior fluoroqui nolone use [158], capreom ycin resistanc e [96], positive sputum smear [167], radiologi cal cavitatio n [88, 89, 158], HIV seroposit ivity [156, 161, 163, 166, 167], other immunocompro mised states [159], history of incarcer ation [92], low body mass index (<18.5 or <20 kg-rrf2) [92, 160], hypoalbu minaemi a [164], older age [89, 158], male sex [154], low haemato crit

[160], and early (<1 yr of treatmen t) default [163] constitut e importan t risk factors for poor outcome s. In a recent systemat ic review of XDR tubercul osis, it was shown that strategie s to support adheren ce, as well as psycholo gical, nutrition al and even financial intervent ions, might further contribut e to improve d outcome s in patients with XDR tubercul osis [170]. Encoura ging results from some countries in Asia and Europe have also suggeste d that manage

ment in specialis ed referenc e centres could improve outcome , although high

success rates could be achieved with treatmen t in some commun ity settings [170].

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The impact of HIV on the outcome s of MDR and XDR tubercul osis has been most serious in South Africa. Among 272 MDR and 382 XDR tubercul osis patients with HIV coinfecti on rates of 90% and 98%, 1yr mortalit y was 71% and 83%, respecti vely. This mortalit y improve d, however , from 2005 to 2007, though the majority of death still occurred within the first 30 days [166]. In the systema tic review mention ed earlier

[170], it was remarke d that addition al data for HIVinfected individu als would be required to determi ne the role of HIV coinfecti on in XDR tubercul osis treatme nt outcome , and to evaluate interven tions that might contribu te to improve outcomes in HIVinfected XDR tubercul osis. The high casefatality rate in the Tugela Ferry outbrea k could represe nt a combina tion of factors at play, not only host immuno compro misation

, but also lack of access to adequat e diagnosi s and treatme nt [170].

end of life for the patient [83, 147].

Pallia tive mana geme nt and endof-life care

MEW DRUGS FOR TREATM ENT OF TUBERC ULOSIS
Mew antitube rculosis drugs are needed to simplify treatme nt )f drugsuscepti ble tubercul osis and to improve outcome of irugresistant tubercul osis [171]. Only four compou nds will be liscusse d in detail for the purpose of this article, as these drugs ippear to have sufficien t potentia l for use in improvin g uberculo sis therapy in the coming decade.

At a certain point in time, recourse to palliativ e care is indicate d for selected patients with "difficult " MDR or XDR tubercul osis, in the interest of both the individu al patient and :he commun ity as a whole. Such manage ment aims to provide uninterr upted medical and psychol ogical care, as well as to ensure a dignified

Sloxif loxaci n

Moxiflox acin is an 8methoxy fluoroqu inolone with a long >lasma half-life of —11 h. It has potent bacterici dal and terilising activity against M. tubercul osis, as shown in murine tudies [172, 173]. In the TB Trials Consorti um (TBTC) Study . 7, a phase II trial, substitut ing moxiflox acin for ethamb utol in he first 8 weeks of therapy did not change the 2month culture tegativit y rates (71%), but there appeare d to be higher activity t earlier time point [174].

However , a study with nearly the ame design conduct ed in Brazil has shown better culture onversio n (80%) in patients receivin g moxiflox acin during the litial phase of treatme nt compare d with the ethamb utol arm 33%) [175]. Another similar phase II clinical study has also hown that patients in the moxiflox acin arm cleared their putum bacilli more quickly [176]. Based on the rapid terilisati on results of the isoniazid -sparing regimen in murine \ odels, TBTC Study

28 was designe d as a doubleblind, lacebocontrolle d study to evaluate 2-month culture converon rates with the substitut ion of moxiflox acin for isoniazid in \e 2month intensiv e phase of treatme nt of pulmona ry iberculo sis. Only a small nonsigni ficant increase in the 2lonth culture negativi ty was achieve d [177]. More rapid :>utum culture conversi on was also observe d with the ddition of moxiflox acin to the standar d shortcourse regimen t a nonrand omised study [178]. In these

studies, moxiflox acin speared to be well tolerate d by most patients, apart from i increase d incidenc e of nausea. QTc interval prolonga tion as observe d in some patients, but this might not have inical significa nce [175, 177]. Further evaluati on of the fluoroqu inolone is ongoing in a phase III REMox study [179]. This study will explore whether moxiflox acin substitut ion for isoniazid or ethamb utol can shorten the conventi onal therapy from 6 to 4 months.

Moxiflox acinand rifapenti nebased regimen s are also under investig ation. It should be noted that, when these drugs are given together , rifapenti ne may induce enzymes that metabolise moxiflox acin, resulting in modestl y reduced moxiflox acin concentr ations [68]. Using a murine model of tubercul osis, regimen s consistin g of isoniazid or moxiflox acin plus rifapentine and pyrazina mide, administ ered either daily or threetimesweekly, were evaluate

d for bacterici dal activity and treatme ntshorteni ng potential . The duration of treatme nt necessar y to achieve stable cure was 10 weeks for daily regimen s and 12 weeks for threetimesweekly regimen s, regardle ss of whether isoniazid or moxiflox acin was used with rifapenti ne and pyrazina mide [180]. By contrast, under the 12week regimen of RHZ, all mice relapsed . The treatme ntshorteni ng potential of more frequent and/or higher doses of rifapenti

ne than 600 mg onceweekly are being explored in both animal experim ents and clinical trials, as discusse d in the section on treatme nt of smearpositive pulmona ry tubercul osis. Further more, in a phase II clinical trial that commen ced in 2009, smearpositive pulmona ry tubercul osis patients were randomi sed in the initial 2 months to receive either Hrifapenti ne-Zmoxiflox acin or RHEZ, followed by the standard nonexpe rimental regimen in the continua tion phase. The efficacy in terms

of sputum conversi on rates and treatme nt outcome s, as well as safety and tolerabili ty of the rifapenti nemoxiflox acincontaini ng regimen s, will thus be evaluate d 181]. Notwiths tanding these somewh at encoura ging results, the high rates of fluoroqui noloneresistant tubercul osis in many parts of the world, especiall y when coincidin g with high disease burden, pose concern regardin g the potential utility of the new fluoroqui nolones in shorteni ng tubercul osis

treatme nt 182]. Regardin g the role of moxiflox acin in the treatme nt of MDR and XDR tubercul osis, there have been some promisin g results lately [183], although the issue of partial crossresistanc e among M. tubercul osis strains is still cause for concern [184].

TMC2 07

TMC207 is a novel diarylqui noline with unique activity on the mycobac terial adenosin e triphosp hate (ATP) synthase [185]. It is active against both drugresistant and -suscepti

ble M. tubercul osis, as well as other mycobac terial species. It has a long half-life in plasma and tissues of nearly 24 h. Data have also suggest ed that TMC207 might kill dormant bacilli as effective ly as aerobica lly grown bacilli. TMC207 is metaboli sed by cytochro me P450 3A4; thus, its plasma level may be reduced by half through interacti on with rifampici n. However , data from a mouse model have demonst rated that TMC207 had significa nt activity, even when its

exposur e was reduced by 50% and it was added to a strong backgro und regimen of RHZ. The bacterici dal effect of TMC207 in mice was modest during the first week of treatme nt but increase d in the following three weeks [186].

TMC207 probably acts synergis - tically with pyrazina mide to exert sterilisat ion activity. In the mouse model, 2-month treatme nt regimen s containi ng TMC207 and pyrazina mide led to sterilisat ion, suggesti ng

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treatme ntshorteni ng potential [187]. In another mouse model study, the triple combina tion of TMC207rifapenti nepvrazinamide, given once weekly, was more active than the current regimen of RHZ given five times per week and led to satisfact ory lung culture negativit y at 2 months [188]. Such unprece dented activity has suggeste d that it might be feasible to develop a fully intermitt ent, onceweekly regimen. In a mouse model to

evaluate the use of TMC207 in MDR tubercul osis, treatme nt was given five times per week with TMC207 alone or various combina tions of TMC207 plus pyrazina mide or other secondline drugs [189]. All TMC207containi ng regimen s were significa ntly more active than the nonTMC207containi ng regimen s after 1 month of therapy. An early bacterici dal activity study with ascendin g doses of TMC207 has demonst rated a delayed onset of

bacteriol ysis, with significa nt activity from day 4-7 when given at a daily dose of 400 mg, which was similar in magnitu de to those of isoniazid and rifampici n over the same period [190]. A doubleblind, randomi sed phase II clinical trial with TMC207 in MDR tubercul osis patients began in 2007 [191]. The study is being conduct ed in two consecut ive stages. In the first explorat ory stage for safety and dose determin ation, newly diagnose d

sputum smearpositive patients with MDR tubercul osis were randomi sed to receive either TMC207 or placebo for 8 weeks on top of a backgro und regimen. The dosing scheme for TMC207 was validate d for further testing in the second stage, being 400 mg daily for 2 weeks followed by 200 mg three times weekly. In the second stage planned for proof of effective ness, patients are randomi sed to receive either TMC207 or placebo for 24 weeks on top of a

backgro und regimen. After finishing 24 weeks of treatme nt, patients will continue to receive MDR tubercul osis treatme nt as per national treatme nt guidelin es. Study subjects will be followed for safety, tolerabili ty, pharmac okinetics and microbio logical efficacy for 96 weeks after receivin g their last dose of TMC207 [191]. Prelimin ary results from the first stage indicate d high efficacy (faster rate and higher proporti on of culture conversi on) and good toleranc e of

TMC207 [192]. Further results are awaited with great interest. Like moxiflox acin, QTc prolonga tion with uncertai n clinical significa nce was observe d in some patients, aside from gastroint estinal upset [192]. TMC207 can have a role in treatme nt of MDR and XDR tubercul osis, subjecte d to confirma tion of its toleranc e and safety on longterm use. Its interacti on with rifampici n might hamper its utility in treatme nt of drugsuscepti ble tubercul osis.

OPC67683
OPC-

67683 is a nitroimid azole with high potency in vitro and in vivo against M. tubercul osis, inclusive of MDR strains. It probably acts through inhibitio n of cell wall biosynth esis, a mechani sm similar to that of PA824 [193], but is ~20 times more potent. OPC67683 and PA824 are closely related compou nds and appear to show crossresistanc e. OPC67683 has a long half-life at ~7-8 h, with no crossresistanc e or antagoni stic activity with first-line antitube rculosis

drugs. In addition, it has promisin g intracell ular postantibioti c effects against M. tubercul osis, compara ble to those of rifampici n [193]. In mice, 2 months of OPC67683rifampici npyrazina mide followed by a further 2 months of OPC67683rifampici n led to complet e culture negativit y, suggesti ng that OPC67683 in combina tion with other existing drugs could potential ly shorten tubercul osis therapy [193]. A randomi sed, doubleblind, multicen tre phase II clinical trial has been

underwa y since 2008 to evaluate its safety, efficacy and pharmac okinetics in the treatme nt of MDR tubercul osis. In the first 56 days, patients receivin g an optimise d backgro und regimen were randomi sed to receive either placebo or OPC67683 at a dose of 100 or 200 mg twicedaily. Thereaft er, the study subjects will complet e their optimise d backgro und regimen [194].

PA824

PA-824 is a nitroimid azopyra n, a class of novel antibact erial agents. It is active

against drugsuscepti ble and -resistan t, and both dividing and nonrepli cating M. tubercul osis [195]. From studying colonyforming unit counts in the lungs of mice, PA- 824 showed bacterici dal activity compara ble to that of isoniazid in the first 8 weeks and sterilisin g activity comparable to that of HR in the continua tion phase [196]. A followup experim ent in mice showed advanta ges in relapse rate with the same combina tion of drugs when

PA-824 was given at a higher dose of 100 mgkg-1 [197]. With the novel combina tion of PA-824moxiflox acinpyrazina mide, mice were cured more rapidly than with the first-line regimen of RHZ, suggesti ng that this combina tion might radically shorten the treatme nt of MDR tubercul osis in humans [198]. No serious adverse events were reported in phase I singleand multipledose trials in healthy voluntee rs [199]. An extende d early bacterici dal activity study

was conduct ed recently in South Africa, evaluati ng the efficacy, safety and pharmac okinetics in newly diagnose d sputum smearpositive patients with drugsuscepti ble tubercul osis [200]. Based on findings from the preclinical and phase I studies, escalatin g doses of PA824 were administ ered for 14 consecut ive days to four groups of patients and compare d with a fifth cohort receivin g standard first-line antitube rculosis treatme nt. The study showed substant

ial and continue d early bacterici dal activity over 14 days with equivale nt efficacy at all doses from a daily dose of 2001,200 mg. One importan t feature of PA824 is its high protein binding (94%). Thus, it is necessar y to ensure that sufficien tly high concentr ations of the free drug can be reached in cavities of pulmona ry tubercul osis to exert bacterici dal activity [201]. Both OPC67683 and PA824 appear to have potential roles in treatme nt of drug-

suscepti ble and -resistan t tubercul osis. Again, the most critical determin ant would be their safety profiles.

Other potent ial candi dates

Two importan t example s of other potential candidat es include a pyrrole derivativ e, LL3858, and a diamine compou nd, SQ109. Both have been subjecte d to phase I testing and further progress is ongoing [55, 202, 203]. Other potential candidat es would be those have both potent bacterici dal and sterilisin g

activities . Example s might include ATP synthase inhibitor s, gyrase inhibitor s and peptide deformyl ase inhibitor s [203]. Aside from these new drugs under develop ment, a

neurolep tic thioridaz ine with impressi ve antitube rculosis activity might also warrant repurpos ing to constitut e a new agent for treating MDR and XDR tubercul osis [204].

EUROPEAN RESPIRATORY journal

45 volume 37 number 1 2

SERIES; TUBERCULOSIS

W.W. YEW ET £_.

A D J U N C T I V E S U R G E R Y
F O R P U L M O N A R Y

T U B E R C U L O S I S
While chemoth erapy using antitube rculosis drugs constitut es the primary treatme nt modality for

pulmona ry tubercul osis, emergen ce of MDR and XDR tubercul osis has rekindle d the enthusia sm in recourse to adjuncti ve surgery to improve the chance of cure in some patients in these drugresistant scenario s [205]. Other indicatio ns of surgical treatme nt of tubercul osis centre on manage ment of empyem a, posttuberculous bronchie ctasis and myceto ma [206]. There are three basic selection criteria

for adjuncti ve surgery in MDR tubercul osis patients [205]. These include: 1) drug resistanc e, as revealed by in vitro suscepti bility testing, is so severe or extensiv e that there is a high probabili ty of failure or relapse with medical therapy alone; 2) the disease is sufficien tly localised that the great prepond erance of radiographica lly discernib le disease can be resected with an expectat ion of adequat e cardiopu lmonary capacity after surgery; and 3) drug activity

is sufficien t to diminish the mycobac terial burden to facilitate healing of bronchia l stump after lung resectio n Patients should receive chemoth erapy prior to surgery for months [205, 207]. If possible, they should be rendere d culturenegative before lung resectio n. However , this may not always occur. In some cases, sputum culture conversi on only appears with prolonge d medical therapy after surgery. Ventilati on/perfu sion scan, pulmona ry

function tests and compute d tomogra phy of the chest are importan t investig ations for preoperativ e assessm ent [205, 206]. For some patients, assessm ent of pulmona ry arterial pressure and bronchia l tree anatomy /patholo gy need to be perform ed. Bilateral disease does not necessar ily preclude surgical intervention, unless extensiv e [208]. Such disease would, however , require staged bilateral resectio n. In experien ced hands, the outcome of lung resectio

n has been found to be rather rewardin g. The cure rates could reach ^90% with pos:surgery chemoth erapy (table 5) [209222]. In resource -limitec areas, the cure rates might be lower (6375%), but

lunz

resectio n still appears useful as adjuncti ve manage ment for this formidab le disease [218]. However , adjuncti ve surger. necessit ates expertis e and financial instillatio n, which are ofter not readily available in many areas where MDR tubercul osa

prevail [223]. Two rather sizable cohort studies have shown that the bes: outcome s in MDR tubercul osis patients were achieved by the use of fluoroqui nolones and adjuncti ve surgery [89, 224 Although there has been no randomi sed study to compare chemoth erapy alone versus combine d chemoth erapy and surgery in the manage ment of MDR tubercul osis, one recen: small series reported significa nt and durable improve men: with lung resectio n and postoperativ e first-

line antitube rculosis chemoth erapy in patients with MDR and XDR tuberculosis [225]. This finding suggests the possibilit y of ar. indepen dent role of lung resectio n in the manage ment of these difficult drugresistant scenario s. With the emergen ce of XDR tubercul osis, adjuncti ve surger. becomes more relevant [121, 226]. Notwiths tanding its use in some patients, the outcome of XDR tubercul osis is generall y worse than that of MDR tubercul osis, with an overall success rate of -50%

[121, 227]. However , in selected patients, sustaine d sputum bacteriol ogical conversi on can be satisfact orily maintain ed [228]. From two large series, patients who had adjuvant surgery experien ced better outcome s [89, 229]. Regardin g the factors governin g outcome of surgery for drugresistant tubercul osis, a

low body mass index (<18.5 kg-rrf" bacillary resistanc e to fluoroqui nolones and presenc e of cavity beyond the range of surgical resectio n portende d poor prognosi s in a carefully perform ed study [219]. The major complica tions of surgical treatme nt of pleuropu lmonarv tubercul osis include broncho pleural fistula, residual space

rCT^gHj Surgical treatment of muitidrug-resistant tubercuiosis#

First author [ref.]

TREASURE [209] VAN LEUVEN [210] SUNG [211] POMERANTZ [212] CHIANG [213] PARK [214] NAIDOO [215] TAKEDA [216] KIR [217] SOMOCURCIO [218] KIM [219] MOHSEN [220] WANG [221] SHIRAISHI [222]
#

n

Patients success % 19 62 27 172 27 49 23 26

Treatment mortality % 89 75 96 98 92 94 96 89

Operative complications % 0

Post-operative 9 23 26 12 11 16 17 14

ÏÏÊSÊÈÊSÊÊÊSÊËffÊÊÊÊÊliÊÎË :
0 3 4 0 0 3

79

95

3

5 23 23 35 25 16

121 79 23 56 56

63 72 96 87 98

5 ; 1 . 4 0 0

: most patients had lung resections in the form of pneumonectomy or lobectomy (a minority also had segmentectomy),

452
volume 37 number 2 EUROPEAN RESPIRATORY journal

W.W. YEW ET AL.

SERIES: TUBE

TB granuloma

Miliary/ disseminated TB

Chemoki nes CCRs

Cytolysis Opsonisatio n Apoptosis ADCC Granul

FIGURE

2,

PM N

ysin perfori 7ILCaseatio n 17 ?ll -21 nFas TNF-ot

Immunopathogenesis dependent cytotoxicity; chemokine double

of

tuberculosis. ADCC: antibodycell-mediated CCR: receptor; Fas: CC DN: cell

negative;

receptor inducing apoptosis; IFN: interferon; IL: interleukin; LpAg: antigen; lipopolysaccharide M0: macrophage;

MHC: major histocompatibility complex antigen; NK: natural killer antigen; antigen; RNI: oxygen reactive ROI: cell; PAg: peptide phosphoPMN: nitrogen reactive TB: TGF: TNF: tumour TPpAg:

polymorphonuclear neutrophil; intermediates; tuberculosis; T-helper necrosis cell;

intermediates;

transforming growth factor; Th: factor; Treg:

regulatory cell.

problems and empyem a. Other complica tions include wound and other infection s, bleeding, cardiovas cular embarras sment, atelectas is and recurrent laryngeal nerve injury. The risk factors for bronchop leural fistula mainly include sputumsmear positivity , low forced expirator y volume in 1 s, old age, and perhaps the techniqu e of stump closure and reinforce ment 230]. There have been no randomis ed controlle d studies that compare d bronchial stump reinforce ment

versus nothing or stapling versus suturing as a means of closure of the stump. Many authoriti es, however, have recomme nded reinforce ment of the bronchial stump, especiall y in selected patients at risk from such complica tions [222, 230]. In some frail patients with MDR tuberculo sis, who usually have limited cardiopul monary reserve and, thus, would not withstan d lung resection , collapse therapy using thoracopl asty 231], plombag e [232] and artificial pneumot horax

european respiratory journal

[233] can be consider ed. Thoracop lasty, aside from causing cosmetic ally unappeal ing deformit y of the thoracic cage, can be associate d with obstructi ve and restrictiv e lung function defects after the procedur e. Extrapleu ral lucite sphere plombag e can give rise to pressure effects, migration and foreignbody irritation problems . The use of artificial pneumot horax has been reapprais ed in a recent study with rather encourag ing radiographic and bacteriol ogical results [233]. In the intervent

ion group, culture negativit y was achieved in all new cases and 81.1% of retreatm ent cases (-80% of the patients had MDR tuberculo sis). Cavity closure occurred in 94.6% and 67.9%, respectiv ely. In the control group, culture negativit y was achieved in 70.9% and 40.0%, respectiv ely, and cavity closure occurred in 56.3% and 24.0% respectiv ely.

ADJUNCT IVE IMMUNO THERAP Y IN TUBERC ULOSIS
Macroph ages, dendritic cells, natural killer cells, yST-cells and CDlrestricted T-cells are

volume 37 number 453 2

involved in the initial cellmediated immune response to M. tubercul osis, and determin e the local or distant progressi on of infection to disease versus containm ent of the infection. Antigens of M. tubercul osis are processe d bv the antigenpresentin g cells. Subsequ ently, CD4+ cells are involved. T-helper (Th) cells, largely CD4+ cells, generally mature into two functiona lly different phenotvp es, often termed Thl and Th2 cells. The former secrete principall y interleuki n (IL)-2 and interfero n (IFN)-v, while the latter

largely secrete or induce IL-4, -5, -6 and -10. IL-12 produced by macroph ages expands Thl cell populatio n and upregula tes its functions . Cellmediated protectiv e immunitv appears to be

associate d with a Thl response [234]. IL18, another cytokine linked to Thl pathway, may also have a putative role in cellmediated protectio n against mycobac terial infection [235]. Tumour necrosis factor (TNF)-a, released largely from macrophages, contribut es to protectin g the host by promotin g granulom a formatio n [236]. However, TNF-a can also cause tissue necrosis under subversiv e T-cell influence . There is some evidence this sabotage effect comes from IL-4 overactiv ity [237]. Figure 2 summari ses the immunop

athogene sis of tuberculosis. Thus, the complex immunop athogene sis of tuberculosis embrace s host tissue inflamma tion and damage, in addition to protectiv e immunity against the tubercle bacilli. Athough a recent in-depth review on the immunot herapy for tubercul osis has revealed a number of potential ly useful agents for immunor egulatio n, immuno augment ation or immuno suppression, no evidence -based recomm endation can yet be formulat ed regardin g their clinical

utility [238]. Adjuncti ve corticost eroids have been used as an attempt to ameliora te inflamm ation. Cochran e reviews have shown improve d mortality of patients with tubercul ous pericardi tis [239] and meningit is [240] with steroid therapy, but inconclusive effects for pericardi al constrict ion. Neurolog ical deficit or disability was improve d among survivors with tubercul ous meningit is. There is currently inadequ ate evidence on whether

steroids are effective in tubercul ous pleural effusion [241]. In HIVinfected patients, steroids have been shown to be beneficia l in tubercul ous meningit is, although the overall prognosi s is still poor [242]. Steroid use in tubercul ous pleural effusion in HIVinfected patients was associat ed with a higher incidenc e of Kaposi's sarcoma [243]. An addition al concern is that adjuvant steroid therapy of HIVrelated tubercul osis has been associat ed with a transient increase

in viral load [244]. In these two latter studies, the dosages of predniso lone used were 50 mgday"1 and 2.75 mg-kg"1 -day"1, respecti vely, with gradual tapering off in 8 weeks [243, 244].
SERIES' TUBERCULOSIS

resistant forms. Table 6 depicts the results of a number of prelimin ary studies regardin g the use of cytokine s (especial ly IFN-y) [246251] and Mycobac terium vaccae (NCTC 11659) [252], an avirulent
W.W. YEW ET AL

Preliminary studies on adjunctive immunotherapy of multidrug-resistant tuberculosis
First author [réf.] Immunomodulator/cytokine Outcome

CONDOS [246] JOHNSON [247] PALMERO [248] GIOSUE [249] GRAHMANN [250] PARK [251] STANFORD [252]

IFN-y (aerosotised)
rhulL-2 (subcutaneous) rlFN-a2b (subcutaneous) IFN-a (aerosolised) IFN-y (aerosolised) IFN-y (subcutaneous)

Baciilary load lowering, radiographic improvement (CT) Reduced baciilary load, radiographic improvement Baciilary load reduction Baciilary load reduction, radiographic improvement (CT) Baciilary load lowering, radiographic improvement No bacteriological conversion on smear and culture, no radiographic improvement (CT) Disease yr: cure rate 82% (1-2 doses); chronic cases: cure rates

Mycobacterium vaccae
(intradermal)

7.6% (1 dose), 37.9% (7 doses), 41.6% (12 doses) I FN: interferon; CT: computed tomography; r: recombinant; hu: human; IL: interleukin.

Cytokine supplem entation was initially thought to be promising adjuncti ve therapy in tubercul osis [245], including drug-

vaccine from a nontuber culous mycobac terial species, in the manage ment of MDR tubercul osis. In a more recent study, nebulise d IFN-ylb

adjuvant therapy was also found to improve constitut ional sympto ms, reduce inflamm atory cytokine s in broncho alveolar lavage and improve clearanc e of acid-fast bacilli from sputum in cavitary pulmona ry tubercul osis [253]. While the results from some of these studies are encoura ging, the limited number of enrolled patients, alongsid e often uncontro lled experim ental designs, leaves great uncertai nty regardin g the definitiv e role of these cytokine s and

allied forms of immunot herapy in tubercul osis treatme nt. By enhancin g mycobac terial killing in macroph ages, vitamin D might have the potential to enable shorteni ng of treatme nt duration for tubercul osis, reducing infectiou sness and improvin g response in drugresistant forms of the disease [254]. However , a doubleblind, randomi sed, placebocontrolle d trial [255] has recently shown that vitamin D, as a supplem entary therapy did not improve clinical

outcome (as assessed by clinical score severity and sputum smear conversi on) among patients with tubercul osis. There was also no overall effect on tubercul osis mortality at 12 months. One caveat might be the possiblv insufficie nt dose of vitamin D used. The clinical role of vitamin D in immunot herapy of tubercul osis is currently uncertai n.

addition, there appear to be some agents that can promote intracell ular killing of M. tubercul osis by macroph ages, through affecting the transpor t of K+ and Ca2+ from the phagolys osome, thereby resulting in better acidificat ion and activatio n of hydrolas es [256]. This might be a promisin g direction of developi ng therapy for drugresistant tubercul osis.

In In 2010, the prevailing challenges of HIV infection and drug resistance still undermine the global control of tuberculosis. With clear indications that XDR tuberculosis results from mismanaged cases of drug-susceptible and MDR tuberculosis, it is imperative to treat drug-susceptible tuberculosis appro-

CONCL USION

priately to completion, and to provide rapid diagnosis, and aggressive as well as appropriate treatment of MDR tuberculosis to avoid the unnecessary development of additional cases of XDR tuberculosis. The main priority interventions would be: 1) strengthening control of tuberculosis, through sound implementation of the Stop TB Strategy, with special focus on laboratory capacities and infection control (including HIV
EUROPEAN RESPIRATORY journal

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W.W. YEW ET AL.

SERIES: TUBERCULOSIS

Grading of evidences for recommendations according to the Scottish Intercollegiate Guidelines Network
Study rating

TABLE 7

Study design

Requirements

Target population Grades of recommendation

High-quality meta-analyses, systematic reviews of RCTs or RCTs with a very low risk of bias Well-conducted meta-analyses, systematic reviews, or RCTs with a low risk of bias As above High-quality case-control/cohort studies or their systemic reviews, with very low risk of confounding/bias and high probability of causal relationship Well-conducted case-control/cohort studies with low risk of confounding/bias and a moderate probability of causal relationship Nonanalytic studies, e.g. case reports, case Directly applicable series Expert opinion

Studies with overall consistency Directly applicable Studies with overall consistency Extrapolated Studies with overall consistency Directly applicable Extrapolated Studies with overall consistency Directly applicable Extrapolated

RCT: randomised controlled trial.

1 + + 1 +
144 -/1 +

control); 2) improvement of programmatic management of drug-resistant tuberculosis, based on updated guidelines, largely from WHO; and 3) promotion of research and development of new diagnostics, vaccines and drugs, as well as other modalities of therapy. While scientific advancement is crucial to better the care of tuberculosis patients and is earnestly awaited, existing tools must be harnessed in sound public health settings to curb the epidemic of tuberculosis today [257].

2 + +
2+

APPENDIX

For Appendix, see table 7.

STATEMENT OF INTEREST
None declared.

>1 study

REFERENCES
1World Health Organization. Global tuberculosis control: a short update to the 2009 report. WHO HTM TB 2009.426. Geneva, WHO, 2009. 2World Health Organization. Multidrug and extensively resistant TB (M/XDR-TB): 2010 global report on surveillance and response. WHO/HTM/TB 2010.3. Geneva, WHO, 2010. 3Scottish Intercollegiate Guidelines Network. SIGN 50: A guideline developer's handbook, Annex B. www.sign.ac.uk/guidelines/ fulltext/50/annexb.html Date last accessed: April 26, 2010. Date last updated: October 27, 2010. 4Mitchison D. Basic mechanisms of chemotherapy Chest 1979; 76: Suppl., 771-781. 5Mitchison DA. The diagnosis and therapy of tuberculosis during the past 100 years. Am J Respir Crit Care Med 2005: 171: 699-706. 6British Thoracic Society. A controlled trial of 6-months' chemotherapy in pulmonary tuberculosis. Final report: Results during the 36-months after the end of chemotherapy and beyond. Br J Dis Chest 1984; 78: 330-336. 7Singapore Tuberculosis Service/British Medical Research Council. Five year follow-up of a clinical trial of three 6month regimens of chemotherapy given intermittently in the continuation phase in the treatment of pulmonary tuberculosis. Am Re~c Respir Dis 1988; 137: 1147-1150. 8China tuberculosis control collaboration. Results of directly observed short-course chemotherapy in 112,842

Chinese patients with smear-positive tuberculosis. Lancet 1996; 347: 358-362. 9Tam CM, Chan SL, Lam CW, et al. Rifapentine and isoniazid in the continuation phase of treating pulmonary tuberculosis: initial report. Am J Respir Crit Care Med 1998; 157: 1726-1733. 10Snider DE Jr, Graczyk J, Bek E, et al. Supervised 6-month treatment of newly diagnosed pulmonary tuberculosis using isoniazid, rifampin, and pyrazinamide with and without streptomycin. Am Rev Respir Dis 1984; 130: 1091-1094. 11Third East African/British Medical Research Council Study. Controlled clinical trial of four short-course regimens of chemotherapy for two durations in the treatment of pulmonary tuberculosis. Tubercle 1980; 61: 59-69. 12Hong Kong Chest Service/British Medical Research Council Study. Controlled trial of 6-month and 8-month regimens in the treatment of pulmonarv tuberculosis. The results up to 24 months. Tubercle 1979; 60: 201210. 13British Thoracic and Tuberculosis Association. Shortcourse chemotherapv in pulmonarv tuberculosis: a controlled trial by the British Thoracic and Tuberculosis Association. Lancet 1976; 2: 1102-1104. 14Slutkin G, Schecter GF, Hopewell PC. The results of 9month isoniazid-rifampin therapy for pulmonary tuberculosis under program conditions in San Francisco. Am Rev Respir Dis 1988; 138: 1622-1624. 15Combs DL, O'Brien RJ, Geiter L. USPHS tuberculosis short- course chemotherapy trial 21: effectiveness, toxicity and acceptability: the report of final results. Ann Intern Med 1990; 112: 397-406. 16World Health Organization. Treatment of tuberculosis. Guidelines, 4th Edn. WHO/HTM/TB/2009.420. Geneva, WHO, 2010. 17Quy HT, Cobelens FG, Lan NT, et al. Treatment outcomes by drug resistance and HIV status among tuberculosis patients in Ho Chi Minh City, Vietnam. Int J Tuberc Lung Dis 2006; 10: 45-51. 18Yew WW. Chemotherapy including drug-resistant therapy and future developments. In: Davies PDO, Barnes PF, Gordon SB, eds. Clinical Tuberculosis, 4th Edn. London, Hodder Arnold, 2008; pp. 225-242. 19Jindani A, Nunn AJ, Enarson DA. Two 8-month regimens of chemotherapy for treatment of newly diagnosed pulmonary

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