Advances in clinical trial design: Weaving tomorrow's TB treatments

Efficacy and safety of higher dose rifampicin in adults with presumed drug-susceptible tuberculosis: an updated systematic review and meta-analysis

Background

Tuberculosis (TB) remains a significant cause of mortality globally, yet first-line treatment has hardly changed for fifty years. The dose of rifampicin, the most important drug in this regimen, has been historically based on pragmatic cost- and risk-benefit considerations. Evidence suggests the current recommended dose (8-12 mg/kg) may not maximise the potential benefits of this drug. We sought to evaluate the efficacy and safety of higher doses of rifampicin in adults with presumed drug-susceptible TB.

Methods

In this systematic review we searched MEDLINE, EMBASE, CENTRAL and Global Health databases for randomised controlled trials up to 31 July 2024 of adults with presumed drug-susceptible TB receiving first-line treatment with an intervention of rifampicin doses higher than currently recommended. Meta-analyses were performed using random effects models where background regimens were the same. Risk ratio was used as the measure for treatment effect. Outcomes of interest related to efficacy and safety.

Findings

Of the 5441 total records identified by our searches, nineteen studies (6332 patients, 31.0% female) were eligible for the systematic review and twelve (3763 patients, 31.0% female) for meta-analysis. Rifampicin doses varied from 8 to 35 mg/kg and implementation of the intervention varied between trials. There was no evidence for increased efficacy with higher doses of rifampicin, however the majority of trials investigated minimally increased doses (up to 20 mg/kg). At higher doses (>20 mg/kg), there may be evidence of increased risk of drug-induced liver injury, albeit with no consistent dose-response relationship.

Interpretation

Evidence on the efficacy of higher doses of rifampicin in the first-line regimen for TB remains incomplete. While higher doses appear generally safe, the risk of drug-induced liver injury may be increased above doses of 20 mg/kg. Larger clinical trials reporting definitive outcomes are needed to determine whether dosing up to 40 mg/kg could safely improve treatment outcomes or reduce duration of first-line therapy.

Funding

WHO, Wellcome Trust.

Target regimen profiles for tuberculosis treatment

Simpler, shorter, safer and more effective treatments for tuberculosis that are easily accessible to all people with tuberculosis are desperately needed. In 2016, the World Health Organization (WHO) developed target regimen profiles for the treatment of tuberculosis to make drug developers aware of both the important features of treatment regimens, and patient and programmatic needs at the country level. In view of recent ground-breaking advances in tuberculosis treatment, WHO has revised and updated these regimen profiles. We used a similar process as for the 2016 profiles, including a baseline treatment landscape analysis, an initial stakeholder survey, modelling studies estimating the impact and cost-effectiveness of novel tuberculosis treatment regimens, and an extensive stakeholder consultation. We developed target regimen profiles for the treatment of rifampicin-susceptible and rifampicin-resistant tuberculosis, as well as a pan-tuberculosis regimen that would be appropriate for patients with any type of tuberculosis. We describe the revised target regimen profile characteristics, with specific minimal and optimal targets to be met, rationale and justification, and aspects relevant to all target regimen profiles (drug susceptibility testing, adherence and forgiveness, treatment strategies, post-tuberculosis lung disease, and cost and access considerations). We discuss the trade-offs of proposed characteristics for decision-making at developmental or operational levels. We expect that, following these target regimen profile revisions, tuberculosis treatment developers will produce regimens that are quality-assured, affordable and widely available, and that meet the needs of affected populations.

Therapeutic developments for tuberculosis and nontuberculous mycobacterial lung disease

Tuberculosis (TB) drug discovery and development has undergone nothing short of a revolution over the past 20 years. Successful public-private partnerships and sustained funding have delivered a much-improved understanding of mycobacterial disease biology and pharmacology and a healthy pipeline that can tolerate inevitable attrition. Preclinical and clinical development has evolved from decade-old concepts to adaptive designs that permit rapid evaluation of regimens that might greatly shorten treatment duration over the next decade. But the past 20 years also saw the rise of a fatal and difficult-to-cure lung disease caused by nontuberculous mycobacteria (NTM), for which the drug development pipeline is nearly empty. Here, we discuss the similarities and differences between TB and NTM lung diseases, compare the preclinical and clinical advances, and identify major knowledge gaps and areas of cross-fertilization. We argue that applying paradigms and networks that have proved successful for TB, from basic research to clinical trials, will help to populate the pipeline and accelerate curative regimen development for NTM disease.

More Tailored Approaches to Tuberculosis Treatment and Prevention

Recent advances in the treatment of tuberculosis (TB) have led to improvements unprecedented in our lifetime. Decades of research in developing new drugs, especially for multidrug-resistant TB, have created not only multiple new antituberculous agents but also a new approach to development and treatment, with a focus on maximizing the benefit to the individual patient. Prevention of TB disease has also been improved and recognized as a critical component of global TB control. While the momentum is positive, it will take continued investment at all levels, especially training of new dedicated TB researchers and advocates around the world, to maintain this progress.

Determining the minimum duration of treatment in tuberculosis: An order restricted non-inferiority trial design

Tuberculosis (TB) is one of the biggest killers among infectious diseases worldwide. Together with the identification of drugs that can provide benefits to patients, the challenge in TB is also the optimisation of the duration of these treatments. While conventional duration of treatment in TB is 6 months, there is evidence that shorter durations might be as effective but could be associated with fewer side effects and may be associated with better adherence. Based on a recent proposal of an adaptive order-restricted superiority design that employs the ordering assumptions within various duration of the same drug, we propose a non-inferiority (typically used in TB trials) adaptive design that effectively uses the order assumption. Together with the general construction of the hypothesis testing and expression for type I and type II errors, we focus on how the novel design was proposed for a TB trial concept. We consider a number of practical aspects such as choice of the design parameters, randomisation ratios, and timings of the interim analyses, and how these were discussed with the clinical team.

Treatment-shortening regimens for tuberculosis: updates and future priorities

In the past 2 years, remarkable advances have been made in shortening tuberculosis (TB) treatment. In particular, four clinical trials (Study 31/A5349, Nix-TB, ZeNix and TB-PRACTECAL) have provided evidence of the efficacy of regimens based on new and repurposed drugs: the 4-month regimen for drug-susceptible TB, and the 6-month bedaquiline-pretomanid-linezolid regimen with or without moxifloxacin for multidrug-resistant/rifampicin-resistant TB. Even if the evidence at the basis of these new regimens is compelling, several questions remain open, particularly concerning linezolid dose finding, the upsurging threat of bedaquiline-resistant Mycobacterium tuberculosis and the feasibility of applying these results to the paediatric population. Several ongoing trials may fill the remaining gaps and produce further reliable evidence to address the outstanding questions in TB treatment shortening.

A Standardized Approach for Collection of Objective Data to Support Outcome Determination for Late-Phase Tuberculosis Clinical Trials

Rationale: We developed a standardized method, possible poor treatment response (PPTR), to help ascertain efficacy endpoints in Study S31/A5349 (NCT02410772), an open-label trial comparing two 4-month rifapentine-based regimens with a standard 6-month regimen for the treatment of pulmonary tuberculosis (TB). Objectives: We describe the use of the PPTR process and evaluate whether the goals of minimizing bias in efficacy endpoint assessment and attainment of relevant data to determine outcomes for all participants were achieved. Methods: A PPTR event was defined as the occurrence of one or more prespecified triggers. Each PPTR required initiation of a standardized evaluation process that included obtaining multiple sputum samples for microbiology. Measurements and Main Results: Among 2,343 participants with culture-confirmed drug-susceptible TB, 454 individuals (19.4%) had a total of 534 individual PPTR events, of which 76.6% were microbiological (positive smear or culture at or after 17 wk). At least one PPTR event was experienced by 92.4% (133 of 144) of participants with TB-related unfavorable outcome and between 13.8% and 14.7% of participants with favorable and not-assessable outcomes. A total of 75% of participants with TB-related unfavorable outcomes had microbiological confirmation of failure to achieve a disease-free cure. Conclusions: Standardized methodologies, such as our PPTR approach, could facilitate unbiased efficacy outcome determinations, improve discrimination between outcomes that are related and unrelated to regimen efficacy, and enhance the ability to conduct pooled analyses of contemporary trials.

Pharmacodynamics and Bactericidal Activity of Combination Regimens in Pulmonary Tuberculosis: Application to Bedaquiline-Pretomanid-Pyrazinamide

A critical barrier to codevelopment of tuberculosis (TB) regimens is a limited ability to identify optimal drug and dose combinations in early-phase clinical testing. While pharmacokinetic-pharmacodynamic (PKPD) target attainment is the primary tool for exposure-response optimization of TB drugs, the PD target is a static index that does not distinguish individual drug contributions to the efficacy of a multidrug combination. A PKPD model of bedaquiline-pretomanid-pyrazinamide (BPaZ) for the treatment of pulmonary TB was developed as part of a dynamic exposure-response approach to regimen development. The model describes a time course relationship between the drug concentrations in plasma and their individual as well as their combined effect on sputum bacillary load assessed by solid culture CFU counts and liquid culture time to positivity (TTP). The model parameters were estimated using data from the phase 2A studies NC-001-(J-M-Pa-Z) and NC-003-(C-J-Pa-Z). The results included a characterization of BPaZ activity as the most and least sensitive to changes in pyrazinamide and bedaquiline exposures, respectively, with antagonistic activity of BPa compensated by synergistic activity of BZ and PaZ. Simulations of the NC-003 study population with once-daily bedaquiline at 200 mg, pretomanid at 200 mg, and pyrazinamide at 1,500 mg showed BPaZ would require 3 months to attain liquid culture negativity in 90% of participants. These results for BPaZ were intended to be an example application with the general approach aimed at entirely novel drug combinations from a growing pipeline of new and repurposed TB drugs.

Anti-tuberculosis treatment strategies and drug development: challenges and priorities

Despite two decades of intensified research to understand and cure tuberculosis disease, biological uncertainties remain and hamper progress. However, owing to collaborative initiatives including academia, the pharmaceutical industry and non-for-profit organizations, the drug candidate pipeline is promising. This exceptional success comes with the inherent challenge of prioritizing multidrug regimens for clinical trials and revamping trial designs to accelerate regimen development and capitalize on drug discovery breakthroughs. Most wanted are markers of progression from latent infection to active pulmonary disease, markers of drug response and predictors of relapse, in vitro tools to uncover synergies that translate clinically and animal models to reliably assess the treatment shortening potential of new regimens. In this Review, we highlight the benefits and challenges of 'one-size-fits-all' regimens and treatment duration versus individualized therapy based on disease severity and host and pathogen characteristics, considering scientific and operational perspectives.

Comparing timelines and evidence available to support new TB, HIV, and HCV drug approvals: The same, only different

Background

Tuberculosis (TB), human immunodeficiency virus (HIV), and hepatitis C virus (HCV) share a global presence and propensity to disproportionately affect marginalized populations. However, over recent decades, many fewer drugs have been brought to market for TB than for the others. Although three new anti-TB drugs have been approved in the US or Europe in the last 10 years, uptake of these drugs has been limited. Using case examples of drugs developed recently for TB, HIV, and HCV, we explore possible reasons. We examine the use and effect of regulatory pathways intended to address weak economic incentives in the face of urgent, unmet needs; evaluate the extent of data underpinning authorizations for these indications; document development timelines and evidence available at the time of each approval; consider explanations for observed differences; and discuss the implications for clinical guidelines and use.

Methods and findings

For each indication, we selected two drugs: one recently approved and one approved between 2012 and 2014, when the first new anti-TB drug from a novel class in more than 40 years received marketing authorization. We calculated time from first published peer-reviewed evidence of activity to date of approval; the number of phase 1, 2, and 3 trials; the number of trial participants randomized to treatment arms containing the drug; and the total number of participants in each trial from the individual drug approval packages. We found that the two TB drugs took longer to gain approval (8.0 and 19.2 years for bedaquiline and pretomanid, respectively) despite availing of special regulatory pathways meant to expedite approval, when compared to the HIV (2.6 years for dolutegravir and 4.7 years for doravirine) and HCV drugs (3.2 and 1.6 years for sofosbuvir and glecaprevir/pibrentasvir, respectively). Moreover, fewer participants were studied prior to TB drug approvals (380 and 879) than prior to approvals for HIV (1598 and 979) and for HCV (2291 and 2448) drugs.

Conclusions

The dramatic disparities observed in TB drug development reaffirm the importance of several actions. Increased investment in TB research and development is necessary to rapidly advance drugs through the pipeline. Development plans and partnerships must provide safety and efficacy evidence on combinations and durations that are relevant to real-world use in heterogeneous populations. Reliable, validated surrogate markers of relapse-free cure are essential to decrease the duration and cost of TB treatment trials and increase the confidence and speed with which new regimens can advance. Lastly, regulators and normative bodies must maintain high evidentiary standards for authorization while ensuring timely and broad approval for TB drugs and regimens.

Prioritising attributes for tuberculosis preventive treatment regimens: a modelling analysis

BACKGROUND

Recent years have seen important improvements in available preventive treatment regimens for tuberculosis (TB), and research is ongoing to develop these further. To assist with the formulation of target product profiles for future regimens, we examined which regimen properties would be most influential in the epidemiological impact of preventive treatment.

METHODS

Following expert consultation, we identified 5 regimen properties relevant to the incidence-reducing impact of a future preventive treatment regimen: regimen duration, efficacy, ease-of-adherence (treatment completion rates in programmatic conditions), forgiveness to non-completion and the barrier to developing rifampicin resistance during treatment. For each regimen property, we elicited expert input for minimally acceptable and optimal (ideal-but-feasible) performance scenarios for future regimens. Using mathematical modelling, we then examined how each regimen property would influence the TB incidence reduction arising from full uptake of future regimens according to current WHO guidelines, in four countries: South Africa, Kenya, India and Brazil.

RESULTS

Of all regimen properties, efficacy is the single most important predictor of epidemiological impact, while ease-of-adherence plays an important secondary role. These results are qualitatively consistent across country settings; sensitivity analyses show that these results are also qualitatively robust to a range of model assumptions, including the mechanism of action of future preventive regimens.

CONCLUSIONS

As preventive treatment regimens against TB continue to improve, understanding the key drivers of epidemiological impact can assist in guiding further development. By meeting these key targets, future preventive treatment regimens could play a critical role in global efforts to end TB.

Analysis of the Clinical Pipeline of Treatments for Drug-Resistant Bacterial Infections: Despite Progress, More Action Is Needed

There is an urgent global need for new strategies and drugs to control and treat multidrug-resistant bacterial infections. In 2017, the World Health Organization (WHO) released a list of 12 antibiotic-resistant priority pathogens and began to critically analyze the antibacterial clinical pipeline. This review analyzes "traditional" and "nontraditional" antibacterial agents and modulators in clinical development current on 30 June 2021 with activity against the WHO priority pathogens mycobacteria and Clostridioides difficile. Since 2017, 12 new antibacterial drugs have been approved globally, but only vaborbactam belongs to a new antibacterial class. Also innovative is the cephalosporin derivative cefiderocol, which incorporates an iron-chelating siderophore that facilitates Gram-negative bacteria cell entry. Overall, there were 76 antibacterial agents in clinical development (45 traditional and 31 nontraditional), with 28 in phase 1, 32 in phase 2, 12 in phase 3, and 4 under regulatory evaluation. Forty-one out of 76 (54%) targeted WHO priority pathogens, 16 (21%) were against mycobacteria, 15 (20%) were against C. difficile, and 4 (5%) were nontraditional agents with broad-spectrum effects. Nineteen of the 76 antibacterial agents have new pharmacophores, and 4 of these have new modes of actions not previously exploited by marketed antibacterial drugs. Despite there being 76 antibacterial clinical candidates, this analysis indicated that there were still relatively few clinically differentiated antibacterial agents in late-stage clinical development, especially against critical-priority pathogens. We believe that future antibacterial research and development (R&D) should focus on the development of innovative and clinically differentiated candidates that have clear and feasible progression pathways to the market.

Practices and trends in clinical trial registration in the Pan African Clinical Trials Registry (PACTR): a descriptive analysis of registration data

BACKGROUND

The Pan African Clinical Trials Registry (PACTR) is a WHO International Clinical Trials Registry Platform primary register, which caters for clinical trials conducted in Africa. PACTR is the first and, at present, the only member of the Network of WHO Primary Registers in Africa. The aim is to describe and report on the trends of trial records registered in PACTR.

METHODS

PACTR was established in 2007 as the AIDS, Tuberculosis, and Malaria Clinical Trials Registry. The scope of the registry was then expanded in 2009 to include all diseases. This is a cross-sectional study of trials registered in PACTR from inception to 18 August 2021. A descriptive analysis of the use and trends of the following data fields: study intervention, disease condition, sex of the participants, sample size, ethics, funding and availability of results was conducted using Microsoft Excel.

RESULTS

The number of trials registered has increased year on year, reaching 606 trials registered in 2020. The total number of trials registered at the time of the analysis was 2998. More than half of the trials in the registry (1655 of 2998, ie, 55%) were prospectively registered. Ethical approval was received by 90% (2691 of 2998) of the registered trials. Factorial assignment as an intervention model was in 20% (589 of 2998) of the trials registered. There were 36% (1083 of 2998) completed trials, of which 3% (94 of 1083) had results available in the registry. The most dominant funding source indicated was self-funding in 23% (693 of 2998) of the registered trials, and 55% (1639 of 2998) had no funding.

CONCLUSION

Registration on PACTR continues to grow; however, our analysis shows that researchers' capacity-building is needed to understand the importance of the registry and how this information informs healthcare decisions. Promoting prospective trial registration remains critical to avoid selective reporting bias to inform research gaps.

An order restricted multi-arm multi-stage clinical trial design

One family of designs that can noticeably improve efficiency in later stages of drug development are multi-arm multi-stage (MAMS) designs. They allow several arms to be studied concurrently and gain efficiency by dropping poorly performing treatment arms during the trial as well as by allowing to stop early for benefit. Conventional MAMS designs were developed for the setting, in which treatment arms are independent and hence can be inefficient when an order in the effects of the arms can be assumed (eg, when considering different treatment durations or different doses). In this work, we extend the MAMS framework to incorporate the order of treatment effects when no parametric dose-response or duration-response model is assumed. The design can identify all promising treatments with high probability. We show that the design provides strong control of the family-wise error rate and illustrate the design in a study of symptomatic asthma. Via simulations we show that the inclusion of the ordering information leads to better decision-making compared to a fixed sample and a MAMS design. Specifically, in the considered settings, reductions in sample size of around 15% were achieved in comparison to a conventional MAMS design.

Mechanism of Action, Resistance, Synergism, and Clinical Implications of Delamanid Against Multidrug-Resistant Mycobacterium tuberculosis

Multidrug-resistant (MDR) isolates of Mycobacterium tuberculosis (MTB) remain a primary global threat to the end of tuberculosis (TB) era. Delamanid (DLM) is a nitro-dihydro-imidazooxazole derivative utilized to treat MDR-TB. DLM has distinct mechanism of action, inhibiting methoxy- and keto-mycolic acid (MA) synthesis through the F420 coenzyme mycobacteria system and generating nitrous oxide. While DLM resistance among MTB strains is uncommon, there are increasing reports in Asia and Europe, and such resistance will prolong the treatment courses of patients infected with MDR-TB. In this review, we address the antimycobacterial properties of DLM, report the global prevalence of DLM resistance, discuss the synergism of DLM with other anti-TB drugs, and evaluate the documented clinical trials to provide new insights into the clinical use of this antibiotic.