WHO group 5 drugs and difficult multidrug-resistant tuberculosis: a systematic review with cohort analysis and meta-analysis

Antitubercular drugs: possible role of natural products acting as antituberculosis medication in overcoming drug resistance and drug-induced hepatotoxicity

Mycobacterium tuberculosis (Mtb) is a pathogenic bacterium which causes tuberculosis (TB). TB control programmes are facing threats from drug resistance. Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains need longer and more expensive treatment with many medications resulting in more adverse effects and decreased chances of treatment outcomes. The World Health Organization (WHO) has emphasised the development of not just new individual anti-TB drugs, but also novel medication regimens as an alternative treatment option for the drug-resistant Mtb strains. Many plants, as well as marine creatures (sponge; Haliclona sp.) and fungi, have been continuously used to treat TB in various traditional treatment systems around the world, providing an almost limitless supply of active components. Natural products, in addition to their anti-mycobacterial action, can be used as adjuvant therapy to increase the efficacy of conventional anti-mycobacterial medications, reduce their side effects, and reverse MDR Mtb strain due to Mycobacterium's genetic flexibility and environmental adaptation. Several natural compounds such as quercetin, ursolic acid, berberine, thymoquinone, curcumin, phloretin, and propolis have shown potential anti-mycobacterial efficacy and are still being explored in preclinical and clinical investigations for confirmation of their efficacy and safety as anti-TB medication. However, more high-level randomized clinical trials are desperately required. The current review provides an overview of drug-resistant TB along with the latest anti-TB medications, drug-induced hepatotoxicity and oxidative stress. Further, the role and mechanisms of action of first and second-line anti-TB drugs and new drugs have been highlighted. Finally, the role of natural compounds as anti-TB medication and hepatoprotectants have been described and their mechanisms discussed.

Primary Disseminated Multidrug-Resistant Tuberculosis of the Lungs, Brain, Meninges, and Abdomen: The World's First Case

Tuberculosis is a highly infectious disease. It usually infects the lung, but dissemination to different organs results in a severe form of tuberculosis, i.e., disseminated tuberculosis. The situation becomes even more challenging when the infection is due to multidrug-resistant strains of Mycobacterium tuberculosis. The present case is a very rare one where a 17-year-old Indian girl presented with headache, vomiting, cough with expectoration, abdominal pain, and a seizure. A diagnostic workup led to the diagnosis of primary disseminated multidrug-resistant tuberculosis of the lungs, brain, meninges, and abdomen. She has been prescribed an anti-tubercular regimen per the national guidelines.

Potential Repurposed Drug Candidates for Tuberculosis Treatment: Progress and Update of Drugs Identified in Over a Decade

The devastating impact of Tuberculosis (TB) has been a menace to mankind for decades. The World Health Organization (WHO) End TB Strategy aims to reduce TB mortality up to 95% and 90% of overall TB cases worldwide, by 2035. This incessant urge will be achieved with a breakthrough in either a new TB vaccine or novel drugs with higher efficacy. However, the development of novel drugs is a laborious process involving a timeline of almost 20-30 years with huge expenditure; on the other hand, repurposing previously approved drugs is a viable technique for overcoming current bottlenecks in the identification of new anti-TB agents. The present comprehensive review discusses the progress of almost all the repurposed drugs that have been identified to the present day (∼100) and are in the development or clinical testing phase against TB. We have also emphasized the efficacy of repurposed drugs in combination with already available frontline anti-TB medications along with the scope of future investigations. This study would provide the researchers a detailed overview of nearly all identified anti-TB repurposed drugs and may assist them in selecting the lead compounds for further in vivo/clinical research.

The pathogenic mechanism of Mycobacterium tuberculosis: implication for new drug development

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a tenacious pathogen that has latently infected one third of the world's population. However, conventional TB treatment regimens are no longer sufficient to tackle the growing threat of drug resistance, stimulating the development of innovative anti-tuberculosis agents, with special emphasis on new protein targets. The Mtb genome encodes ~4000 predicted proteins, among which many enzymes participate in various cellular metabolisms. For example, more than 200 proteins are involved in fatty acid biosynthesis, which assists in the construction of the cell envelope, and is closely related to the pathogenesis and resistance of mycobacteria. Here we review several essential enzymes responsible for fatty acid and nucleotide biosynthesis, cellular metabolism of lipids or amino acids, energy utilization, and metal uptake. These include InhA, MmpL3, MmaA4, PcaA, CmaA1, CmaA2, isocitrate lyases (ICLs), pantothenate synthase (PS), Lysine-ε amino transferase (LAT), LeuD, IdeR, KatG, Rv1098c, and PyrG. In addition, we summarize the role of the transcriptional regulator PhoP which may regulate the expression of more than 110 genes, and the essential biosynthesis enzyme glutamine synthetase (GlnA1). All these enzymes are either validated drug targets or promising target candidates, with drugs targeting ICLs and LAT expected to solve the problem of persistent TB infection. To better understand how anti-tuberculosis drugs act on these proteins, their structures and the structure-based drug/inhibitor designs are discussed. Overall, this investigation should provide guidance and support for current and future pharmaceutical development efforts against mycobacterial pathogenesis.

Relationship Between Linezolid Exposure and the Typical Clinical Laboratory Safety and Bacterial Clearance in Chinese Pediatric Patients

Objectives: There have been limited studies concerning the safety and efficacy of linezolid (LZD) in children. This study aimed to evaluate the association between LZD exposure and clinical safety and efficacy in Chinese pediatric patients.

Methods: This retrospective cross-sectional study included patients ≤18 years of age who received ≥3 days of LZD treatment between 31 January 2015, and 31 December 2020. Demographic characteristics, medication information, laboratory test information, and bacterial culture results were collected from the Hospital Information System (HIS). Exposure was defined as AUC₂₄ and calculated by the non-linear mixed-effects modeling program (NONMEM), version 7.2, based on two validated population pharmacokinetic models. Binary logistic regression analyses were performed to analyze the associations between AUC₂₄ and laboratory adverse events, and receiver operating characteristic curves were used to calculate the cut-off values. Efficacy was evaluated by bacterial clearance.

Results: A total of 413 paediatric patients were included, with an LZD median (interquartile range) dose, duration, clearance and AUC₂₄ of 30.0 (28.1-31.6) mg/kg/day, 8 (4‒15) days,1.31 (1.29-1.32) L/h and 81.1 (60.6-108.7) mg/L·h, respectively. Adverse events associated with TBil, AST, ALT, PLT, hemoglobin, WBC, and neutrophil count increased during and after LZD treatment when compared with before medication (p < 0.05), and the most common adverse events were thrombocytopaenia (71/399, 17.8%) and low hemoglobin (61/401, 15.2%) during the LZD treatment. Patients with AUC₂₄ higher than 120.69 mg/L h might be associated with low hemoglobin 1–7 days after the end of the LZD treatment, and those with an AUC₂₄ higher than 92.88 mg/L∙h might be associated with thrombocytopaenia 8–15 days after the end of the LZD treatment. A total of 136 patients underwent bacterial culture both before and after LZD treatment, and the infection was cleared in 92.6% (126/136) of the patients, of whom 69.8% (88/126) had AUC₂₄/MIC values greater than 80.

Conclusion: Hematological indicators should be carefully monitored during LZD treatment, especially thrombocytopaenia and low hemoglobin, and a continuous period of monitoring after LZD withdrawal is also necessary. Since the AUC₂₄ cut-off values for laboratory adverse events were relatively low, a trade-off is necessary between the level of drug exposure required for treatment and safety, and the exposure target (AUC₂₄/MIC) in pediatric patients should be further studied, especially for patients with complications and concomitant medications.

Hematologic Toxicity of Linezolid in Multidrug Resistant and Extensively Drug Resistant Tuberculosis (MDR/XDR-TB): the role of mitochondria

Multidrug-resistant tuberculosis (MDR-TB) is caused by an organism that is resistant to both rifampicin and isoniazid. Extensively drug-resistant TB, a rare type of MDR-TB, is caused by an organism that is resistant to quinolone and one of group A TB drugs (i.e., linezolid and bedaquiline). In 2018, the World Health Organization revised the groupings of TB medicines and reclassified linezolid as a group A drug for the treatment of MDR-TB. Linezolid is a synthetic antimicrobial agent in the oxazolidinone class. Although linezolid has a good efficacy, it can cause substantial adverse events, especially hematologic toxicity. In both TB infection and linezolid mechanism of action, mitochondrial dysfunction plays an important role. In this concise review, characteristics of linezolid as an anti-TB drug are summarized, including its efficacy, pathogenesis of hematologic toxicity highlighting mitochondrial dysfunction, and the monitoring and management of hematologic toxicity.

Multidisciplinary management of difficult-to-treat drug resistant tuberculosis: a review of cases presented to the national consilium in Uganda

BACKGROUND

Patients with drug resistant tuberculosis (DR-TB) with comorbidities and drug toxicities are difficult to treat. Guidelines recommend such patients to be managed in consultation with a multidisciplinary team of experts (the "TB consilium") to optimise treatment regimens. We describe characteristics and treatment outcomes of DR-TB cases presented to the national DR-TB consilium in Uganda between 2013 and 2019.

METHODS

We performed a secondary analysis of data from a nation-wide retrospective cohort of DR-TB patients with poor prognostic indicators in Uganda. Patients had a treatment outcome documented between 2013 and 2019. Characteristics and treatment outcomes were compared between cases reviewed by the consilium with those that were not reviewed.

RESULTS

Of 1,122 DR-TB cases, 189 (16.8%) cases from 16 treatment sites were reviewed by the consilium, of whom 86 (45.5%) were reviewed more than once. The most frequent inquiries (N = 308) from DR-TB treatment sites were construction of a treatment regimen (38.6%) and management of side effects (24.0%) while the most frequent consilium recommendations (N = 408) were a DR-TB regimen (21.7%) and "observation while on current regimen" (16.6%). Among the cases reviewed, 152 (80.4%) were from facilities other than the national referral hospital, 113 (61.1%) were aged ≥ 35 years, 72 (40.9%) were unemployed, and 26 (31.0%) had defaulted antiretroviral therapy. Additionally, 141 (90.4%) had hepatic injury, 55 (91.7%) had bilateral hearing loss, 20 (4.8%) had psychiatric symptoms and 14 (17.7%) had abnormal baseline systolic blood pressure. Resistance to second-line drugs (SLDs) was observed among 9 (4.8%) cases while 13 (6.9%) cases had previous exposure to SLDs. Bedaquiline (13.2%, n = 25), clofazimine (28.6%, n = 54), high-dose isoniazid (22.8%, n = 43) and linezolid (6.7%, n = 13) were more frequently prescribed among cases reviewed by the consilium than those not reviewed. Treatment success was observed among 126 (66.7%) cases reviewed.

CONCLUSION

Cases reviewed by the consilium had several comorbidities, drug toxicities and a low treatment success rate. Consilia are important "gatekeepers" for new and repurposed drugs. There is need to build capacity of lower health facilities to construct DR-TB regimens and manage adverse effects.

Early treatment outcome of bedaquiline plus optimised background regimen in drug resistant tuberculosis patients

AIMS

Bedaquiline (BDQ) has been recently approved for drug resistant tuberculosis with active drug safety monitoring under programmatic condition. The present study was conducted to evaluate safety, tolerability and efficacy of bedaquiline plus optimised background regimen.

METHODS

A prospective study was conducted on cohort of pre-extensively drug resistant (XDR) and XDR pulmonary TB patients. Eligible patients were closely monitored for cardiac safety, adverse events (AEs), clinical and microbiological improvement during BDQ (6 months) and post BDQ phase for twelve months.

RESULTS

Of 127 patients enrolled, a significant increase in mean QTc interval was observed on 13th day and 3rd week as compared to baseline (p < 0.0001). Mean maximum increase of QTc was 37.92ms (95% CI, 14.1-61.74ms). Concomitant anti-TB medications, age, gender, low body mass index (BMI) had significant effect on QTc prolongation (p < 0.0001, p < 0.05). However, none of the patient required discontinuation of BDQ. Majority of AEs (86.3%) were non-serious and not preventable 108 (87.1%). The median time for sputum-culture conversion was 40.89 ± 3.5 days (95% CI, 34-48 days) and the treatment outcome was successful in 102 (80.3%) patients with negative sputum culture conversion.

CONCLUSIONS

Bedaquiline containing regimen achieved favourable outcome. Although, bedaquiline along with concomitant anti-TB medications has the potential to prolong QTc interval, the benefit certainly outweighs the risk. This calls for a through pre-treatment cardiovascular and biochemical evaluation as a preventive measure and appropriate selection of patients for safe use of BDQ and successful outcome.

An overview of new antitubercular drugs, drug candidates, and their targets

The causative agent of tuberculosis (TB), Mycobacterium tuberculosis and more recently totally drug-resistant strains of M. tuberculosis, display unique mechanisms to survive in the host. A four-drug treatment regimen was introduced 40 years ago but the emergence of multidrug-resistance and more recently TDR necessitates the identification of new targets and drugs for the cure of M. tuberculosis infection. The current efforts in the drug development process are insufficient to completely eradicate the TB epidemic. For almost five decades the TB drug development process remained stagnant. The last 10 years have made sudden progress giving some new and highly promising drugs including bedaquiline, delamanid, and pretomanid. Many of the candidates are repurposed compounds, which were developed to treat other infections but later, exhibited anti-TB properties also. Each class of drug has a specific target and a definite mode of action. These targets are either involved in cell wall biosynthesis, protein synthesis, DNA/RNA synthesis, or metabolism. This review discusses recent progress in the discovery of newly developed and Food and Drug Administration approved drugs as well as repurposed drugs, their targets, mode of action, drug-target interactions, and their structure-activity relationship.

Factors affecting outcomes of individualised treatment for drug resistant tuberculosis in an endemic region

BACKGROUND

Individualised treatment regimens for drug resistant tuberculosis have improved outcomes. This retrospective observational study examined potential factors that affect individualised treatment in an endemic region, and highlighted predictors of a successful outcome.

METHODS

We examined records of proven MDR, pre-XDR and XDR TB patients diagnosed and started on treatment between 2010 and 2014, and collected the following data for each patient: age, gender, comorbidities, past history of TB, diagnosis, site of disease, drug susceptibility testing (DST) results, treatment, adverse reactions to anti-tubercular drugs, treatment changes and outcomes, which were recorded as positive, negative or neutral. Tests of association were carried out between factors and outcomes, following which multiple logistic regression analysis was done to determine the predictors of a positive outcome such as patient cured after completion of treatment at 18 months or longer.

RESULTS

Fifty-nine patients completed treatment at our centre. The median age was 26 years (range 8-65 years). There were 31 (52.5%) female patients. Forty-four (74.6%) were successfully treated over a median treatment period of 23 months (range 18-30 months). Successful outcomes were associated with age less than 45 years (P=0.01, OR=6.67, 95% CI=1.73-23.47), resistance to fewer than five drugs (P=0.001, OR=9.51, 95% CI=2.50-38.18) and susceptibility to Group 4 drugs (P=0.04, OR=4.71, 95% CI=1.03-16.83).

CONCLUSIONS

Age and drug susceptibility were important predictors of treatment outcome.

Effectiveness of interventions for reducing TB incidence in countries with low TB incidence: a systematic review of reviews

AIMS

What is the evidence base for the effectiveness of interventions to reduce tuberculosis (TB) incidence in countries which have low TB incidence?

METHODS

We conducted a systematic review of interventions for TB control and prevention relevant to low TB incidence settings (<10 cases per 100 000 population). Our analysis was stratified according to "direct" or "indirect" effects on TB incidence. Review quality was assessed using AMSTAR2 criteria. We summarised the strength of review level evidence for interventions as "sufficient", "tentative", "insufficient" or "no" using a framework based on the consistency of evidence within and between reviews.

RESULTS

We found sufficient review level evidence for direct effects on TB incidence/case prevention of vaccination and treatment of latent TB infection. We also found sufficient evidence of beneficial indirect effects attributable to drug susceptibility testing and adverse indirect effects (measured as sub-optimal treatment outcomes) in relation to use of standardised first-line drug regimens for isoniazid-resistant TB and intermittent dosing regimens. We found insufficient review level evidence for direct or indirect effects of interventions in other areas, including screening, adherence, multidrug-resistant TB, and healthcare-associated infection.

DISCUSSION

Our review has shown a need for stronger evidence to support expert opinion and country experience when formulating TB control policy.

Linezolid for drug-resistant pulmonary tuberculosis

BACKGROUND

Linezolid was recently re-classified as a Group A drug by the World Health Organization (WHO) for treatment of multi-drug resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), suggesting that it should be included in the regimen for all patients unless contraindicated. Linezolid use carries a considerable risk of toxicity, with the optimal dose and duration remaining unclear. Current guidelines are mainly based on evidence from observational non-comparative studies.

OBJECTIVES

To assess the efficacy of linezolid when used as part of a second-line regimen for treating people with MDR and XDR pulmonary tuberculosis, and to assess the prevalence and severity of adverse events associated with linezolid use in this patient group.

SEARCH METHODS

We searched the following databases: the Cochrane Infectious Diseases Specialized Register; CENTRAL; MEDLINE; Embase; and LILACS up to 13 July 2018. We also checked article reference lists and contacted researchers in the field.

SELECTION CRITERIA

We included studies in which some participants received linezolid, and others did not. We included randomized controlled trials (RCTs) of linezolid for MDR and XDR pulmonary tuberculosis to evaluate efficacy outcomes. We added non-randomized cohort studies to evaluate adverse events.Primary outcomes were all-cause and tuberculosis-associated death, treatment failure, and cure. Secondary outcomes were treatment interrupted, treatment completed, and time to sputum culture conversion. We recorded frequency of all and serious adverse events, adverse events leading to drug discontinuation or dose reduction, and adverse events attributed to linezolid, particularly neuropathy, anaemia, and thrombocytopenia.

DATA COLLECTION AND ANALYSIS

Two review authors (BS and DC) independently assessed the search results for eligibility and extracted data from included studies. All review authors assessed risk of bias using the Cochrane 'Risk of bias' tool for RCTs and the ROBINS-I tool for non-randomized studies. We contacted study authors for clarification and additional data when necessary.We were unable to perform a meta-analysis as one of the RCTs adopted a study design where participants in the study group received linezolid immediately and participants in the control group received linezolid after two months, and therefore there were no comparable data from this trial. We deemed meta-analysis of non-randomized study data inappropriate.

MAIN RESULTS

We identified three RCTs for inclusion. One of these studies had serious problems with allocation of the study drug and placebo, so we could not analyse data for intervention effect from it. The remaining two RCTs recruited 104 participants. One randomized 65 participants to receive linezolid or not, in addition to a background regimen; the other randomized 39 participants to addition of linezolid to a background regimen immediately, or after a delay of two months. We included 14 non-randomized cohort studies (two prospective, 12 retrospective), with a total of 1678 participants.Settings varied in terms of income and tuberculosis burden. One RCT and 7 out of 14 non-randomized studies commenced recruitment in or after 2009. All RCT participants and 38.7% of non-randomized participants were reported to have XDR-TB.Dosing and duration of linezolid in studies were variable and reported inconsistently. Daily doses ranged from 300 mg to 1200 mg; some studies had planned dose reduction for all participants after a set time, others had incompletely reported dose reductions for some participants, and most did not report numbers of participants receiving each dose. Mean or median duration of linezolid therapy was longer than 90 days in eight of the 14 non-randomized cohorts that reported this information.Duration of participant follow-up varied between RCTs. Only five out of 14 non-randomized studies reported follow-up duration.Both RCTs were at low risk of reporting bias and unclear risk of selection bias. One RCT was at high risk of performance and detection bias, and low risk for attrition bias, for all outcomes. The other RCT was at low risk of detection and attrition bias for the primary outcome, with unclear risk of detection and attrition bias for non-primary outcomes, and unclear risk of performance bias for all outcomes. Overall risk of bias for the non-randomized studies was critical for three studies, and serious for the remaining 11.One RCT reported higher cure (risk ratio (RR) 2.36, 95% confidence interval (CI) 1.13 to 4.90, very low-certainty evidence), lower failure (RR 0.26, 95% CI 0.10 to 0.70, very low-certainty evidence), and higher sputum culture conversion at 24 months (RR 2.10, 95% CI 1.30 to 3.40, very low-certainty evidence), amongst the linezolid-treated group than controls, with no differences in other primary and secondary outcomes. This study also found more anaemia (17/33 versus 2/32), nausea and vomiting, and neuropathy (14/33 versus 1/32) events amongst linezolid-receiving participants. Linezolid was discontinued early and permanently in two of 33 (6.1%) participants who received it.The other RCT reported higher sputum culture conversion four months after randomization (RR 2.26, 95% CI 1.19 to 4.28), amongst the group who received linezolid immediately compared to the group who had linezolid initiation delayed by two months. Linezolid was discontinued early and permanently in seven of 39 (17.9%) participants who received it.Linezolid discontinuation occurred in 22.6% (141/624; 11 studies), of participants in the non-randomized studies. Total, serious, and linezolid-attributed adverse events could not be summarized quantitatively or comparatively, due to incompleteness of data on duration of follow-up and numbers of participants experiencing events.

AUTHORS' CONCLUSIONS

We found some evidence of efficacy of linezolid for drug-resistant pulmonary tuberculosis from RCTs in participants with XDR-TB but adverse events and discontinuation of linezolid were common. Overall, there is a lack of comparative data on efficacy and safety. Serious risk of bias and heterogeneity in conducting and reporting non-randomized studies makes the existing, mostly retrospective, data difficult to interpret. Further prospective cohort studies or RCTs in high tuberculosis burden low-income and lower-middle-income countries would be useful to inform policymakers and clinicians of the efficacy and safety of linezolid as a component of drug-resistant TB treatment regimens.

Curving Tuberculosis: Current Trends and Future Needs

Tuberculosis (TB) presents new challenges as a global public health problem, especially at a time of increasing threats to some particular patients due to Human Immunodeficiency Virus (HIV) infection and multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis. The World Health Assembly strives to reduce TB deaths by 95% and to decrease TB incidence by 95% by 2035. However, new approaches are necessary in order to attain these objectives. Such approaches include active ascertainment of cases in high risk populations, increasing the availability of accurate point-of-care testing, rapid detection of drug resistance, novel vaccines, and new prophylaxis and treatment regimens (particularly for MDR and XDR TB). The ultimate objective of those programs is to develop highly effective drug regimens that can achieve high cure rates regardless of strains’ resistance patterns.

Rapid detection of drug-resistant Mycobacterium tuberculosis directly from clinical specimens using allele-specific polymerase chain reaction assay

Background & objectives:

Rapid detection of drug resistance in Mycobacterium tuberculosis (MTB) is essential for the efficient control of tuberculosis. Hence, in this study a nested-allele-specific (NAS) PCR, nested multiple allele-specific PCR (NMAS-PCR) and multiple allele-specific (MAS) PCR assays were evaluated that enabled detection of the most common mutations responsible for isoniazid (INH) and rifampicin (RIF) resistance in MTB isolates directly from clinical specimens.

Methods:

Six pairs of primers, mutated and wild type, were used for the six targets such as codon 516, 526 and 531 of rpoB, codon 315 of katG and C15-T substitution in the promoter region of mabA-inhA using allele-specific (AS) PCR assays (NAS-PCR, NMAS-PCR and MAS-PCR). The performance of AS PCR method was compared with phenotypic drug susceptibility testing (DST).

Results:

The usefulness of AS PCR assays was evaluated with 391 clinical specimens (251 Acid fast bacilli smear positive and MTB culture positive; 93 smear negative and MTB culture positive; 47 smear positive and MTB culture negative) and 344 MTB culture positive isolates. With culture-based phenotypic DST as a reference standard, the sensitivity and specificity of the NAS-PCR, NMAS-PCR and MAS-PCR assay for drug resistance-related genetic mutation detection were 98.6 and 97.8 per cent for INH, 97.5 and 97.9 per cent for RIF and 98.9 and 100 per cent for multidrug resistance (MDR).

Interpretation & conclusions:

The performance of AS PCR assays showed that those could be less expensive and technically executable methods for rapid detection of MDR-TB directly from clinical specimens.

Assessment of the Additional Value of Verapamil to a Moxifloxacin and Linezolid Combination Regimen in a Murine Tuberculosis Model

The favorable treatment outcome rate for multidrug-resistant tuberculosis (MDR-TB) is only 54%, and therefore new drug regimens are urgently needed. In this study, we evaluated the activity of the combination of moxifloxacin and linezolid as a possible new MDR-TB regimen in a murine TB model and the value of the addition of the efflux pump inhibitor verapamil to this backbone. BALB/c mice were infected with drug-sensitive Mycobacterium tuberculosis and were treated with human-equivalent doses of moxifloxacin (200 mg/kg of body weight) and linezolid (100 mg/kg) with or without verapamil (12.5 mg/kg) for 12 weeks. Pharmacokinetic parameters were collected during treatment at the steady state. After 12 weeks of treatment, a statistically significant decline in mycobacterial load in the lungs was observed with the moxifloxacin-linezolid regimen with and without verapamil (5.9 and 5.0 log CFU, respectively), but sterilization was not achieved yet. The spleens of all mice were culture negative after 12 weeks of treatment with both treatment modalities, and the addition of verapamil caused a significant reduction in relapse (14/14 positive spleens without versus 9/15 with verapamil, P = 0.017). In conclusion, treatment with a combination regimen of moxifloxacin and linezolid showed a strong decline in mycobacterial load in the mice. The addition of verapamil to this backbone had a modest additional effect in terms of reducing mycobacterial load in the lung as well as reducing the spleen relapse rate. These results warrant further studies on the role of efflux pump inhibition in improving the efficacy of MDR-TB backbone regimens.

New drugs and regimens for tuberculosis

Since standardized rifampin-based first-line regimens and fluoroquinolone-based second-line regimens were used to treat tuberculosis (TB), unfortunately without timely modification according to the drug resistance profile, TB and drug-resistant disease are still important public health threats worldwide. Although the last decade has witnessed advances in rapid diagnostic tools and use of repurposed and novel drugs for better managing drug-resistant TB, we need an appropriate TB control strategy and a well-functioning health infrastructure to ensure optimal operational use of rapid tests, judicious use of effective treatment regimens that can be rapidly tailored according to the drug resistance profile and timely management of risk factors and co-morbidities that promote infection and its progression to disease. We searched the published literature to discuss (i) standardized versus individualized therapies, including the choice between a single one-size-fit-all regimen versus different options with different key drugs determined mainly by rapid drug susceptibility testing, (ii) alternative regimens for managing drug-susceptible TB, (iii) evidence for using the World Health Organization (WHO) longer and shorter regimens for multidrug-resistant TB and (iv) evidence for using repurposed and novel drugs. We hope an easily applicable combination of biomarkers that accurately predict individual treatment outcome will soon be available to ultimately guide individualized therapy.

Drug-resistant tuberculosis: An update on disease burden, diagnosis and treatment

The emergence of antimicrobial resistance against Mycobacterium tuberculosis, the leading cause of mortality due to a single microbial pathogen worldwide, represents a growing threat to public health and economic growth. The global burden of multidrug-resistant tuberculosis (MDR-TB) has recently increased by an annual rate of more than 20%. According to the World Health Organization approximately only half of all patients treated for MDR-TB achieved a successful outcome. For many years, patients with drug-resistant tuberculosis (TB) have received standardized treatment regimens, thereby accelerating the development of MDR-TB through drug-specific resistance amplification. Comprehensive drug susceptibility testing (phenotypic and/or genotypic) is necessary to inform physicians about the best drugs to treat individual patients with tailor-made treatment regimens. Phenotypic drug resistance can now often, but with variable sensitivity, be predicted by molecular drug susceptibility testing based on whole genome sequencing, which in the future could become an affordable method for the guidance of treatment decisions, especially in high-burden/resource-limited settings. More recently, MDR-TB treatment outcomes have dramatically improved with the use of bedaquiline-based regimens. Ongoing clinical trials with novel and repurposed drugs will potentially further improve cure-rates, and may substantially decrease the duration of MDR-TB treatment necessary to achieve relapse-free cure.

Treatment outcomes of rifabutin-containing regimens for rifabutin-sensitive multidrug-resistant pulmonary tuberculosis

OBJECTIVES

The aim of this study was to evaluate whether rifabutin can improve treatment outcomes in patients with rifabutin-sensitive MDR-TB.

METHODS

A retrospective cohort study was performed on 76 patients with rifabutin-sensitive MDR-TB who were treated with or without rifabutin between 2006 and 2011.

RESULTS

Overall, 75% (57/76) of patients achieved favorable outcomes, including cure (53/76, 70%) and treatment completion (4/76, 5%). In contrast, 25% (19/76) had unfavorable treatment outcomes, which included treatment failure (6/76, 8%), death (2/76, 3%), loss to follow-up (4/76. 5%), and no evaluation due to transfer to other institutions (7/76, 9%). Rifabutin was given to 52 (68%) of the 76 patients with rifabutin-sensitive MDR-TB. Although favorable treatment outcomes were more frequent in patients who received rifabutin [81% (42/52)] than in those who did not receive rifabutin [63% (15/24)], this difference was not statistically significant (P=0.154). However, in multivariable regression logistic analysis, use of rifabutin was significantly associated with favorable treatment outcomes in patients with rifabutin-sensitive MDR-TB (adjusted odds ratio=9.80, 95% confidence interval=1.65-58.37, P=0.012).

CONCLUSIONS

These results suggest that the use of rifabutin can improve treatment outcomes in patients with rifabutin-sensitive MDR-TB.

Clofazimine for Treatment of Extensively Drug-Resistant Pulmonary Tuberculosis in China

We performed a multicenter, prospective, randomized study to investigate the efficacy and safety of clofazimine (CLO) for treatment of extensively drug-resistant tuberculosis (XDR-TB) in China. Forty-nine patients infected with XDR-TB were randomly assigned to either the control group or the CLO group, both of which received 36 months of individually customized treatment. The primary endpoint was the time to sputum culture conversion on solid medium. Clinical outcomes of patients were evaluated at the time of treatment completion. Of the 22 patients in the experimental group, 7 (31.8%) met the treatment criterion of "cure" and 1 (4.5%) "complete treatment," for a total of 8 (36.4%) exhibiting successful treatment outcomes without relapse. In the control group, 6 patients (22.2%) were cured and 6 (22.2%) completed treatment by the end of the study. Statistical analysis revealed no significant difference in successful outcome rates between the CLO group and the control group. The average sputum culture conversion time for the experimental group was 19.7 months, which was not statistically different from that for the control group (20.3 months; P = 0.57). Of the 22 patients in the CLO group, 12 (54.5%) experienced adverse events after starting CLO treatment. The most frequently observed adverse event was liver damage, with 31.8% of patients (7/22 patients) in the CLO group versus 11.1% (3/27 patients) in the control group exhibiting this adverse event. Our study demonstrates that inclusion of CLO in background treatment regimens for XDR-TB is of limited benefit, especially since hepatic disorders arise as major adverse events with CLO treatment. (This study is registered with the Chinese Clinical Trial Registry [ChiCTR, www.chictr.org.cn] under identifier ChiCTR1800014800.).

Interleukin-17 regulates matrix metalloproteinase activity in human pulmonary tuberculosis

Tuberculosis (TB) is characterized by extensive pulmonary matrix breakdown. Interleukin-17 (IL-17) is key in host defence in TB but its role in TB-driven tissue damage is unknown. We investigated the hypothesis that respiratory stromal cell matrix metalloproteinase (MMP) production in TB is regulated by T-helper 17 (TH -17) cytokines. Biopsies of patients with pulmonary TB were analysed by immunohistochemistry (IHC), and patient bronchoalveolar lavage fluid (BALF) MMP and cytokine concentrations were measured by Luminex assays. Primary human airway epithelial cells were stimulated with conditioned medium from human monocytes infected with Mycobacterium tuberculosis (Mtb) and TH -17 cytokines. MMP secretion, activity, and gene expression were determined by ELISA, Luminex assay, zymography, RT-qPCR, and dual luciferase reporter assays. Signalling pathways were examined using phospho-western analysis and siRNA. IL-17 is expressed in TB patient granulomas and MMP-3 is expressed in adjacent pulmonary epithelial cells. IL-17 had a divergent, concentration-dependent effect on MMP secretion, increasing epithelial secretion of MMP-3 (p < 0.001) over 72 h, whilst decreasing that of MMP-9 (p < 0.0001); mRNA levels were similarly affected. Both IL-17 and IL-22 increased fibroblast Mtb-dependent MMP-3 secretion but IL-22 did not modulate epithelial MMP-3 expression. Both IL-17 and IL-22, but not IL-23, were significantly up-regulated in BALF from TB patients. IL-17-driven MMP-3 was dependent on p38 MAP kinase and the PI3K p110α subunit. In summary, IL-17 drives airway stromal cell-derived MMP-3, a mediator of tissue destruction in TB, alone and with monocyte-dependent networks in TB. This is regulated by p38 MAP kinase and PI3K pathways. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Susceptibilities of MDR Mycobacterium tuberculosis isolates to unconventional drugs compared with their reported pharmacokinetic/pharmacodynamic parameters

Background

The second-line drugs recommended to treat drug-resistant TB are toxic, expensive and difficult to procure. Given increasing resistance, the need for additional anti-TB drugs has become more urgent. But new drugs take time to develop and are expensive. Some commercially available drugs have reported anti-mycobacterial activity but are not routinely used because supporting laboratory and clinical evidence is sparse.

Methods

We analysed 217 MDR M. tuberculosis isolates including 153 initial isolates from unique patients and 64 isolates from follow-up specimens during the course of treatment. The resazurin microdilution assay was performed to determine MICs of trimethoprim/sulfamethoxazole, mefloquine, thioridazine, clofazimine, amoxicillin/clavulanate, meropenem/clavulanate, nitazoxanide, linezolid and oxyphenbutazone. Isoniazid was used for validation. We calculated the MIC 50 and MIC 90 as the MICs at which growth of 50% and 90% of isolates was inhibited, respectively.

Results

The MIC 50 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.2/4; mefloquine, 8; thioridazine, 4; clofazimine, 0.25; amoxicillin/clavulanate, 16/8; meropenem/clavulanate, 1/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 40. The MIC 90 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.4/8; mefloquine, 8; thioridazine, 8; clofazimine, 0.5; amoxicillin/clavulanate, 32/16; meropenem/clavulanate, 8/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 60. By comparison, the MIC 90 of isoniazid was >4 mg/L, as expected. There was no evidence that previous treatment affected susceptibility to any drug.

Conclusions

Most drugs demonstrated efficacy against M. tuberculosis . When these MICs are compared with the published pharmacokinetic/pharmacodynamic profiles of the respective drugs in humans, trimethoprim/sulfamethoxazole, meropenem/clavulanate, linezolid, clofazimine and nitazoxanide appear promising and warrant further clinical investigation.

In Vitro Isolation and Characterization of Oxazolidinone-Resistant Mycobacterium tuberculosis

Oxazolidinones are promising candidates for the treatment of Mycobacterium tuberculosis infections. We isolated linezolid-resistant strains from H37Rv (Euro-American) and HN878 (East-Asian) strains; resistance frequencies were similar in the two strains. Mutations were identified in ribosomal protein L3 (RplC) and the 23S rRNA (rrl). All mutant strains were cross resistant to sutezolid; a subset was cross resistant to chloramphenicol. Mutations in rrl led to growth impairment and decreased fitness that may limit spread in clinical settings.

WHO Treatment Guidelines for Drug-Resistant Tuberculosis, 2016 Update: Applicability in South Korea

Despite progress made in tuberculosis control worldwide, the disease burden and treatment outcome of multidrug-resistant tuberculosis (MDR-TB) patients have remained virtually unchanged. In 2016, the World Health Organization released new guidelines for the management of MDR-TB. The guidelines are intended to improve detection rate and treatment outcome for MDR-TB through novel, rapid molecular testing and shorter treatment regimens. Key changes include the introduction of a new, shorter MDR-TB treatment regimen, a new classification of medicines and updated recommendations for the conventional MDR-TB regimen. This paper will review these key changes and discuss the potential issues with regard to the implementation of these guidelines in South Korea.

Therapy of Multidrug-Resistant and Extensively Drug-Resistant Tuberculosis

The global epidemic of multidrug-resistant tuberculosis (MDR-TB) caused by Mycobacterium tuberculosis strains resistant to at least isoniazid and rifampin was recently reported as larger than previously estimated, with at least 580,000 new cases reported in 2015. Extensively drug-resistant tuberculosis (XDR-TB), MDR-TB with additional resistance to a second-line fluoroquinolone and injectable, continues to account for nearly 10% of MDR cases globally. Cases in India, China, and the Russian Federation account for >45% of the cases of MDR-TB. Molecular testing helps identify MDR more quickly, and treatment options have expanded across the globe. Despite this, only 20% are in treatment, and treatment is challenging due to the toxicity of medications and the long duration. In 2016 the World Health Organization updated guidelines for the treatment of MDR-TB. A new short-course regimen is an option for those who qualify. Five effective drugs, including pyrazinamide (PZA) when possible, are recommended during the initial treatment phase and four drugs thereafter. Revised drug classifications include the use of linezolid and clofazimine as key second-line drugs and the option to use bedaquiline and delamanid to complete a five-drug regimen when needed due to poor medication tolerance or extensive resistance. Despite multiple drugs and long-duration treatment regimens, the outcomes for MDR and especially XDR-TB are much worse than for drug-susceptible disease. Better management of toxicity, prevention of transmission, and identification and appropriate management of infected contacts are important challenges for the future.

Clofazimine-Containing Regimen for the Treatment of Mycobacterium abscessus Lung Disease

Patients with lung disease caused by Mycobacterium abscessus subsp. abscessus (here M. abscessus) typically have poor treatment outcomes. Although clofazimine (CFZ) has been increasingly used in the treatment of M. abscessus lung disease in clinical practice, there are no reported data on its effectiveness for this disease. This study sought to evaluate the clinical efficacy of a CFZ-containing regimen for the treatment of M. abscessus lung disease. We performed a retrospective review of the medical records of 42 patients with M. abscessus lung disease who were treated with CFZ-containing regimens between November 2013 and January 2015. CFZ was administered in combination with other antibiotics as an initial antibiotic regimen in 15 (36%) patients (initial treatment group), and it was added to an existing antibiotic regimen for refractory M. abscessus lung disease in 27 (64%) patients (salvage treatment group). Overall, there was an 81% treatment response rate based on symptoms and a 31% response rate based on radiographic findings. Conversion to culture-negative sputum samples was achieved in 10 (24%) patients after CFZ-containing antibiotic treatment, and during treatment, there were significant decreases in the positivity of semiquantitative sputum cultures for acid-fast bacilli in both the initial (P = 0.018) and salvage (P = 0.001) treatment groups. Our study suggests that CFZ-containing regimens may improve treatment outcomes in patients with M. abscessus lung disease and that a prospective evaluation of CFZ in M. abscessus lung disease is warranted.

An updated systematic review and meta-analysis for treatment of multidrug-resistant tuberculosis

This systematic review aimed to update the current evidence for multidrug-resistant tuberculosis (MDR-TB) treatment.We searched for studies that reported treatment information and clinical characteristics for at least 25 patients with microbiologically confirmed pulmonary MDR-TB and either end of treatment outcomes, 6-month culture conversion or severe adverse events (SAEs). We assessed the association of these outcomes with patients' characteristics or treatment parameters. We identified 74 studies, including 17 494 participants.The pooled treatment success was 26% in extensively drug-resistant TB (XDR-TB) patients and 60% in MDR-TB patients. Treatment parameters such as number or duration and individual drugs were not associated with improved 6-month sputum culture conversion or end of treatment outcomes. However, MDR-TB patients that received individualised regimens had higher success than patients who received standardised regimens (64% versus 52%; p<0.0.01). When reports from 20 cohorts were pooled, proportions of SAE ranged from 0.5% attributed to ethambutol to 12.2% attributed to para-aminosalicylic acid. The lack of significant associations of treatment outcomes with specific drugs or regimens may reflect the limitations of pooling the data rather than a true lack of differences in efficacy of regimens or individual drugs.This analysis highlights the need for stronger evidence for treatment of MDR-TB from better-designed and reported studies.

The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

Global tuberculosis incidence has declined marginally over the past decade, and tuberculosis remains out of control in several parts of the world including Africa and Asia. Although tuberculosis control has been effective in some regions of the world, these gains are threatened by the increasing burden of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. XDR tuberculosis has evolved in several tuberculosis-endemic countries to drug-incurable or programmatically incurable tuberculosis (totally drug-resistant tuberculosis). This poses several challenges similar to those encountered in the pre-chemotherapy era, including the inability to cure tuberculosis, high mortality, and the need for alternative methods to prevent disease transmission. This phenomenon mirrors the worldwide increase in antimicrobial resistance and the emergence of other MDR pathogens, such as malaria, HIV, and Gram-negative bacteria. MDR and XDR tuberculosis are associated with high morbidity and substantial mortality, are a threat to health-care workers, prohibitively expensive to treat, and are therefore a serious public health problem. In this Commission, we examine several aspects of drug-resistant tuberculosis. The traditional view that acquired resistance to antituberculous drugs is driven by poor compliance and programmatic failure is now being questioned, and several lines of evidence suggest that alternative mechanisms-including pharmacokinetic variability, induction of efflux pumps that transport the drug out of cells, and suboptimal drug penetration into tuberculosis lesions-are likely crucial to the pathogenesis of drug-resistant tuberculosis. These factors have implications for the design of new interventions, drug delivery and dosing mechanisms, and public health policy. We discuss epidemiology and transmission dynamics, including new insights into the fundamental biology of transmission, and we review the utility of newer diagnostic tools, including molecular tests and next-generation whole-genome sequencing, and their potential for clinical effectiveness. Relevant research priorities are highlighted, including optimal medical and surgical management, the role of newer and repurposed drugs (including bedaquiline, delamanid, and linezolid), pharmacokinetic and pharmacodynamic considerations, preventive strategies (such as prophylaxis in MDR and XDR contacts), palliative and patient-orientated care aspects, and medicolegal and ethical issues.

Group 5 drugs for multidrug-resistant tuberculosis: individual patient data meta-analysis

The role of so-called "group 5" second-line drugs as a part of antibiotic therapy for multidrug-resistant tuberculosis (MDR-TB) is widely debated. We performed an individual patient data meta-analysis to evaluate the effectiveness of several group 5 drugs including amoxicillin/clavulanic acid, thioacetazone, the macrolide antibiotics, linezolid, clofazimine and terizidone for treatment of patients with MDR-TB.Detailed individual patient data were obtained from 31 published cohort studies of MDR-TB therapy. Pooled treatment outcomes for each group 5 drug were calculated using a random effects meta-analysis. Primary analyses compared treatment success to a combined outcome of failure, relapse or death.Among 9282 included patients, 2191 received at least one group 5 drug. We found no improvement in treatment success among patients taking clofazimine, amoxicillin/clavulanic acid or macrolide antibiotics, despite applying a number of statistical approaches to control confounding. Thioacetazone was associated with increased treatment success (OR 2.6, 95% CI 1.1-6.1) when matched controls were selected from studies in which the group 5 drugs were not used at all, although this result was heavily influenced by a single study.The development of more effective antibiotics to treat drug-resistant TB remains an urgent priority.

Population-Based Drug Resistance Surveillance of Multidrug-Resistant Tuberculosis in Taiwan, 2007-2014

Objective

To determine the extent of drug resistance in multidrug-resistant tuberculosis (MDR-TB) cases, we conducted a retrospective, population-based analysis using drug susceptibility testing (DST) results of MDR Mycobacterium tuberculosis complex isolates obtained from 2007–2014 in Taiwan.

Methods

M. tuberculosis isolates collected from 1,331 MDR-TB cases were included in this survey. Treatment histories, age, sex, chest radiograph and bacteriological results of patients were analyzed. Standard DST was performed to assess resistance to the following drugs: isoniazid (INH), rifampicin (RIF), streptomycin (SM), ethambutol (EMB), amikacin (AM), kanamycin (KM), capreomycin (CAP), ofloxacin (OFX), moxifloxacin (MOX), levofloxacin (LVX), gatifloxacin (GAT), para-aminosalicylate (PAS), ethionamide (EA), and pyrazinamide (PZA). The Cochran-Armitage trend test was used for statistical analysis.

Results

We observed a significant increasing trend in portion of new MDR-TB cases, from 59.5% to 80.2% (p < 0.0001), and significant decreasing trend of portion in the 15-44-year-old age group (p < 0.05). Of the MDR M. tuberculosis isolates tested, 6.2% were resistant to AM, 8.6% were resistant to KM, 4.6% were resistant to CAP, 19.5% were resistant to OFX, 17.1% were resistant to MOX, 16.0% were resistant to LVX, 5.8% were resistant to GAT, 9.5% were resistant to PAS, 28.5% were resistant to EA and 33.3% were resistant to PZA. Fifty (3.8%) extensively drug-resistant TB cases were identified. No significant differences were found in drug resistance frequencies between new and previously treated MDR cases. However, we observed significant decreases in the rates of AM resistance (p < 0.05), OFX resistance (p < 0.00001), PAS resistance (p < 0.00001), EA resistance (p < 0.05) and PZA resistance (p < 0.05). Moreover, younger age groups had higher rates of resistance to fluoroquinolones.

Conclusion

A policy implemented in 2007 to restrict the prescription of fluoroquinolones was shown to be effective. Our survey revealed a decreasing trend of resistance to PZA, OFX and AM, which suggests the feasibility of adopting a short-course regimen and demonstrates the effectiveness of our management program for MDR-TB.

Pyrazinamide Resistance Assays and Two-Month Sputum Culture Status in Patients with Multidrug-Resistant Tuberculosis

Phenotypic drug susceptibility testing is the current "gold standard" for detecting Mycobacterium tuberculosis susceptibility to antituberculous drugs. Pyrazinamide is one antituberculous drug for which the correlation between in vitro resistance and clinical outcomes remains unclear. Here we performed latent class analysis (LCA) to develop a consensus gold standard definition of pyrazinamide resistance using three paired standard pyrazinamide resistance assays. We then compared this consensus measure to the 2-month culture results for patients with multidrug-resistant tuberculosis (MDR-TB) who were treated for 2 months with first-line antituberculous drugs before their resistance results were known. Among 121 patients with MDR-TB, 60 (49.6%) were resistant to pyrazinamide by the Wayne method (L. G. Wayne, Am Rev Respir Dis 109:147-151, 1974), 71 (58.7%) were resistant by the Bactec MGIT 960 method, and 68 (56.2%) were resistant by pncA sequencing. LCA grouped isolates with positive results by at least two assays into a category which we considered the "consensus gold standard" for pyrazinamide resistance. The sensitivity and specificity for this consensus gold standard were 82.4% and 92.5%, respectively, for the Wayne method; 95.6% and 88.7%, respectively, for the Bactec MGIT 960 method; and 92.6% and 90.6%, respectively, for pncA sequencing. After we adjusted for other factors associated with poor outcomes, including age, sex, alcohol use, and baseline ethambutol resistance, patients whose isolates were resistant by the LCA-derived consensus gold standard were more likely to be culture positive at 2 months with an odds ratio of 1.95 (95% confidence interval, 0.74 to 5.11), but this result was not statistically significant. These findings underscore the need for improved diagnostics for routine use in programmatic settings.

Clinical management of adults and children with multidrug-resistant and extensively drug-resistant tuberculosis

BACKGROUND

Globally there is a burgeoning epidemic of drug monoresistant tuberculosis (TB), multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB). Almost 20% of all TB strains worldwide are resistant to at least one major TB drug, including isoniazid. In several parts of the world there is an increasing incidence of MDR-TB, and alarmingly, almost a third of MDR-TB cases globally are resistant to either a fluoroquinolone or aminoglycoside. This trend cannot be ignored because drug-resistant TB is associated with greater morbidity compared to drug-susceptible TB, accounts for almost 25% of global TB mortality, is extremely costly to treat, consumes substantial portions of budgets allocated to national TB programmes in TB-endemic countries and is a major threat to healthcare workers, who are already in short supply in resource-poor settings. Even more worrying is the growing epidemic of resistance beyond XDR-TB, including resistance to newer drugs such as bedaquiline and delamanid, as well as the increasing prevalence of programmatically incurable TB in countries like South Africa, Russia, India and China. These developments threaten to reverse the gains already made against TB.

SOURCES

Articles related to MDR-TB and XDR-TB found on PubMed in all languages up to September 2016, published reviews, and files of the authors.

AIM AND CONTENT

To review the clinical management of adults and children with MDR- and XDR-TB with a particular emphasis on the utility of newer and repurposed drugs such as linezolid, bedaquiline and delamanid, as well as management of MDR- and XDR-TB in special situations such as in HIV-infected persons and in children.

IMPLICATIONS

This review informs on the prevention, diagnosis, and clinical management of MDR-TB and XDR-TB.

Drug resistance mechanisms and novel drug targets for tuberculosis therapy

Drug-resistant tuberculosis (TB) poses a significant challenge to the successful treatment and control of TB worldwide. Resistance to anti-TB drugs has existed since the beginning of the chemotherapy era. New insights into the resistant mechanisms of anti-TB drugs have been provided. Better understanding of drug resistance mechanisms helps in the development of new tools for the rapid diagnosis of drug-resistant TB. There is also a pressing need in the development of new drugs with novel targets to improve the current treatment of TB and to prevent the emergence of drug resistance in Mycobacterium tuberculosis. This review summarizes the anti-TB drug resistance mechanisms, furnishes some possible novel drug targets in the development of new agents for TB therapy and discusses the usefulness using known targets to develop new anti-TB drugs. Whole genome sequencing is currently an advanced technology to uncover drug resistance mechanisms in M. tuberculosis. However, further research is required to unravel the significance of some newly discovered gene mutations in their contribution to drug resistance.

New Antituberculosis Drugs: From Clinical Trial to Programmatic Use

Treatment of multidrug-resistant tuberculosis (MDR-TB) cases is challenging because it relies on second-line drugs that are less potent and more toxic than those used in the clinical management of drug-susceptible TB. Moreover, treatment outcomes for MDR-TB are generally poor compared to drug sensitive disease, highlighting the need for of new drugs. For the first time in more than 50 years, two new anti-TB drugs were approved and released. Bedaquiline is a first-in-class diarylquinoline compound that showed durable culture conversion at 24 weeks in phase IIb trials. Delamanid is the first drug of the nitroimidazole class to enter clinical practice. Similarly to bedaquiline results of phase IIb studies showed increased sputum-culture conversion at 2 months and better final treatment outcomes in patients with MDR-TB. Among repurposed drugs linezolid and carbapenems may represent a valuable drug to treat cases of MDR and extensively drug-resistant TB. The recommended regimen for MDR-TB is the combination of at least four drugs to which M. tuberculosis is likely to be susceptible for the duration of 20 months. Drugs are chosen with a stepwise selection process through five groups on the basis of efficacy, safety, and cost. Clinical phase III trials on new regimen are ongoing that could prove transformative against MDR-TB, by being shorter (six months), simpler (an all-oral regimen) and safer than current standard therapy. It is fundamental that the adoption of the new drugs is done responsibly to avoid inappropriate use. Concentration of in-patient MDR-TB treatment in specialized centers could be considered in countries with low numbers of cases in order to provide appropriate clinical case management and to prevent emergence of drug resistance.

A Case of Disseminated Multidrug-Resistant Tuberculosis involving the Brain

We report a case of a 23-year-old female immigrant from China who was diagnosed with multidrug-resistant tuberculosis affecting her lung and brain, resistant to the standard first-line therapeutics and streptomycin. She was treated with prothionamide, moxifloxacin, cycloserine, and kanamycin. However, her headache and brain lesion worsened. After the brain biopsy, the patient was confirmed with intracranial tuberculoma. Linezolid was added to intensify the treatment regimen, and steroid was added for the possibility of paradoxical response. Kanamycin was discontinued 6 months after initiation of the treatment; she was treated for 18 months with susceptible drugs and completely recovered. To our knowledge, this case is the first multidrug-resistant tuberculosis that disseminated to the brain in Korea.

Role of the Cys154Arg Substitution in Ribosomal Protein L3 in Oxazolidinone Resistance in Mycobacterium tuberculosis

We expressed the wild-type rplC and mutated rplC (Cys154Arg) genes, respectively, in Mycobacterium tuberculosis H37Ra and H37Rv in an attempt to delineate the role of rplC (Cys154Arg) regarding oxazolidinone resistance. An increase of the MICs of linezolid (LZD) and sutezolid (PNU-100480, PNU) against the recombinant mycobacteria with overexpressed rplC mutation (Cys154Arg) was found, suggesting the rplC gene is a determinant of bacillary susceptibilities to LZD and PNU.

Tuberculosis

Although the worldwide incidence of tuberculosis has been slowly decreasing, the global disease burden remains substantial (∼9 million cases and ∼1·5 million deaths in 2013), and tuberculosis incidence and drug resistance are rising in some parts of the world such as Africa. The modest gains achieved thus far are threatened by high prevalence of HIV, persisting global poverty, and emergence of highly drug-resistant forms of tuberculosis. Tuberculosis is also a major problem in health-care workers in both low-burden and high-burden settings. Although the ideal preventive agent, an effective vaccine, is still some time away, several new diagnostic technologies have emerged, and two new tuberculosis drugs have been licensed after almost 50 years of no tuberculosis drugs being registered. Efforts towards an effective vaccine have been thwarted by poor understanding of what constitutes protective immunity. Although new interventions and investment in control programmes will enable control, eradication will only be possible through substantial reductions in poverty and overcrowding, political will and stability, and containing co-drivers of tuberculosis, such as HIV, smoking, and diabetes.

Issues Related to the Updated 2014 Korean Guidelines for Tuberculosis

Tuberculosis (TB) remains a major public health problem in South Korea. The Joint Committee for the Development of Korean Guidelines for Tuberculosis published the Korean Guidelines for Tuberculosis in 2011 to provide evidence-based practical recommendations to health care workers caring for patients with TB in South Korea. After reviewing recent national and international scientific data on TB, the committee updated the Korean guidelines for TB in 2014. This article presents some practical issues related to the 2014 updated guidelines: namely use of the Mycobacterium tuberculosis - polymerase chain reaction assay and the Xpert MTB/RIF assay in the diagnosis of TB, as well as medical treatment for patients with multidrug-resistant TB.

Emerging strategies for the treatment of pulmonary tuberculosis: promise and limitations?

A worsening scenario of drug-resistant tuberculosis has increased the need for new treatment strategies to tackle this worldwide emergency. There is a pressing need to simplify and shorten the current 6-month treatment regimen for drug-susceptible tuberculosis. Rifamycins and fluoroquinolones, as well as several new drugs, are potential candidates under evaluation. At the same time, treatment outcomes of patients with drug-resistant tuberculosis should be improved through optimizing the use of fluoroquinolones, repurposed agents and newly developed drugs. In this context, the safety and tolerance of new therapeutic approaches must be addressed.

Susceptibility testing breakpoints for Mycobacterium tuberculosis categorize isolates with resistance mutations in gyrA as susceptible to fluoroquinolones: implications for MDR-TB treatment and the definition of XDR-TB

OBJECTIVES

Fluoroquinolones (FQs) are important in the treatment of MDR-TB and in the definition of XDR-TB. Our objective was to investigate how discrepancies in the phenotypic and genotypic methods for antimicrobial susceptibility testing could affect the interpretation of antimicrobial susceptibility test results.

METHODS

We analysed MICs of ofloxacin and levofloxacin in Middlebrook 7H10 broth (7H10) as well as sequencing of the quinolone resistance-determining region of the gyrA gene and the MTBDRsl assay in 75 resistant isolates, including MDR and XDR strains of Mycobacterium tuberculosis.

RESULTS

Among 75 resistant isolates, 27 had mutations associated with FQ resistance. Among isolates with resistance mutations in gyrA, 26% (seven of 27) were susceptible to levofloxacin and ofloxacin by phenotypic testing at 1 mg/L and 2 mg/L. The most common mutation was in codon 94 and these isolates had significantly increased MICs of levofloxacin (2-8 mg/L) compared with isolates with mutations in codon 90 (0.25-2 mg/L, P < 0.05). The sensitivity and specificity for the MTBDRsl assay compared with gyrA sequencing were 96% and 98%, respectively.

CONCLUSION

Current critical concentrations may classify up to 26% of isolates with gyrA mutations as susceptible to FQs due to a close relationship between susceptible and resistant populations. These results should be considered while improving clinical breakpoints for M. tuberculosis and may have an impact on the definition of XDR-TB.

Probing the chemical mechanism and critical regulatory amino acid residues of Drosophila melanogaster arylalkylamine N-acyltransferase like 2

Arylalkylamine N-acyltransferase like 2 (AANATL2) catalyzes the formation of N-acylarylalkylamides from the corresponding acyl-CoA and arylalkylamine. The N-acylation of biogenic amines in Drosophila melanogaster is a critical step for the inactivation of neurotransmitters, cuticle sclerotization, and melatonin biosynthesis. In addition, D. melanogaster has been used as a model system to evaluate the biosynthesis of fatty acid amides: a family of potent cell signaling lipids. We have previously showed that AANATL2 catalyzes the formation of N-acylarylakylamides, including long-chain N-acylserotonins and N-acyldopamines. Herein, we define the kinetic mechanism for AANATL2 as an ordered sequential mechanism with acetyl-CoA binding first followed by tyramine to generate the ternary complex prior to catalysis. Bell shaped kcat,app - acetyl-CoA and (kcat/Km)app - acetyl-CoA pH-rate profiles identified two apparent pKa,app values of ∼7.4 and ∼8.9 that are critical to catalysis, suggesting the AANATL2-catalyzed formation of N-acetyltyramine occurs through an acid/base chemical mechanism. Site-directed mutagenesis of a conserved glutamate that corresponds to the catalytic base for other D. melanogaster AANATL enzymes did not produce a substantial depression in the kcat,app value nor did it abolish the pKa,app value attributed to the general base in catalysis (pKa ∼7.4). These data suggest that AANATL2 catalyzes the formation of N-acylarylalkylamides using either different catalytic residues or a different chemical mechanism relative to other D. melanogaster AANATL enzymes. In addition, we constructed other site-directed mutants of AANATL2 to help define the role of targeted amino acids in substrate binding and/or enzyme catalysis.

Contribution of Oxazolidinones to the Efficacy of Novel Regimens Containing Bedaquiline and Pretomanid in a Mouse Model of Tuberculosis

New regimens based on two or more novel agents are sought to shorten or simplify treatment of tuberculosis (TB). Pretomanid (PMD) is a nitroimidazole in phase 3 trials that has significant bactericidal activity alone and in combination with bedaquiline (BDQ) and/or pyrazinamide (PZA). We previously showed that the novel combination of BDQ+PMD plus the oxazolidinone sutezolid (SZD) had sterilizing activity superior to that of the first-line regimen in a murine model of TB. The present experiments compared the activity of different oxazolidinones in combination with BDQ+PMD with or without PZA in the same model. The 3-drug regimen of BDQ+PMD plus linezolid (LZD) had sterilizing activity approaching that of BDQ+PMD+SZD and superior to that of the first-line regimen. The addition of PZA further enhanced activity. Reducing the duration of LZD to 1 month did not significantly affect the activity of the regimen. Halving the LZD dose or replacing LZD with RWJ-416457 modestly reduced activity over the first month but not after 2 months. AZD5847 and tedizolid also increased the bactericidal activity of BDQ+PMD, but they were less effective than the other oxazolidinones. These results provide optimism for safe, short-course oral regimens for drug-resistant TB that may also be superior to the current first-line regimen for drug-susceptible TB.

Efficacy and safety of World Health Organization group 5 drugs for multidrug-resistant tuberculosis treatment

The efficacy and toxicity of several drugs now used to treat multidrug-resistant tuberculosis (MDR-TB) have not been fully evaluated.

We searched three databases for studies assessing efficacy in MDR-TB or safety during prolonged treatment of any mycobacterial infections, of drugs classified by the World Health Organization as having uncertain efficacy for MDR-TB (group 5).

We included 83 out of 4002 studies identified. Evidence was inadequate for meropenem, imipenem and terizidone. For MDR-TB treatment, clarithromycin had no efficacy in two studies (risk difference (RD) −0.13, 95% CI −0.40–0.14) and amoxicillin–clavulanate had no efficacy in two other studies (RD 0.07, 95% CI −0.21–0.35). The largest number of studies described prolonged use for treatment of non-tuberculous mycobacteria. Azithromycin was not associated with excess serious adverse events (SAEs). Clarithromycin was not associated with excess SAEs in eight controlled trials in HIV-infected patients (RD 0.00, 95% CI −0.02–0.02), nor in six uncontrolled studies in HIV-uninfected patients, whereas six uncontrolled studies in HIV-infected patients clarithromycin caused substantial SAEs (proportion 0.20, 95% CI 0.12–0.27).

For most group 5 drugs we found inadequate evidence of safety for prolonged use or for efficacy for MDR-TB, although macrolides appeared to be safe in prolonged use.