Evaluation of six months sputum culture conversion as a surrogate endpoint in a multidrug resistant-tuberculosis trial

Sputum culture reversion in longer treatments with bedaquiline, delamanid, and repurposed drugs for drug-resistant tuberculosis

Sputum culture reversion after conversion is an indicator of tuberculosis (TB) treatment failure. We analyze data from the endTB multi-country prospective observational cohort (NCT03259269) to estimate the frequency (primary endpoint) among individuals receiving a longer (18-to-20 month) regimen for multidrug- or rifampicin-resistant (MDR/RR) TB who experienced culture conversion. We also conduct Cox proportional hazard regression analyses to identify factors associated with reversion, including comorbidities, previous treatment, cavitary disease at conversion, low body mass index (BMI) at conversion, time to conversion, and number of likely-effective drugs. Of 1,286 patients, 54 (4.2%) experienced reversion, a median of 173 days (97-306) after conversion. Cavitary disease, BMI < 18.5, hepatitis C, prior treatment with second-line drugs, and longer time to initial culture conversion were positively associated with reversion. Reversion was uncommon. Those with cavitary disease, low BMI, hepatitis C, prior treatment with second-line drugs, and in whom culture conversion is delayed may benefit from close monitoring following conversion.

Comparative effectiveness of adding delamanid to a multidrug-resistant tuberculosis regimen comprised of three drugs likely to be effective

Clarity about the role of delamanid in longer regimens for multidrug-resistant TB is needed after discordant Phase IIb and Phase III randomized controlled trial results. The Phase IIb trial found that the addition of delamanid to a background regimen hastened culture conversion; the results of the Phase III trial were equivocal. We evaluated the effect of adding delamanid for 24 weeks to three-drug MDR/RR-TB regimens on two- and six-month culture conversion in the endTB observational study. We used pooled logistic regression to estimate the observational analogue of the intention-to-treat effect (aITT) adjusting for baseline confounders and to estimate the observational analogue of the per-protocol effect (aPP) using inverse probability of censoring weighting to control for time-varying confounding. At treatment initiation, 362 patients received three likely effective drugs (delamanid-free) or three likely effective drugs plus delamanid (delamanid-containing). Over 80% of patients received two to three Group A drugs (bedaquiline, linezolid, moxifloxacin/levofloxacin) in their regimen. We found no evidence the addition of delamanid to a three-drug regimen increased two-month (aITT relative risk: 0.90 (95% CI: 0.73-1.11), aPP relative risk: 0.89 (95% CI: 0.66-1.21)) or six-month culture conversion (aITT relative risk: 0.94 (95% CI: 0.84, 1.02), aPP relative risk: 0.93 (95% CI: 0.83, 1.04)). In regimens containing combinations of three likely effective, highly active anti-TB drugs the addition of delamanid had no discernible effect on culture conversion at two or six months. As the standard of care for MDR/RR-TB treatment becomes more potent, it may become increasingly difficult to detect the benefit of adding a single agent to standard of care MDR/RR-TB regimens. Novel approaches like those implemented may help account for background regimens and establish effectiveness of new chemical entities.

Favorable outcome of individual regimens containing bedaquiline and delamanid in drug-resistant tuberculosis: A systematic review

Background

Drug-resistant tuberculosis (DR-TB) is a public health concern that is difficult to treat, requiring long and complex treatment with highly effective drugs. Bedaquiline and/or delamanid have already shown promising outcomes in patients with DR-TB, increasing the rate of culture conversion and lowering TB-related mortality.

Methods

We comprehensively searched and evaluated the effectiveness of individual regimens containing bedaquiline and delamanid on culture conversion and treatment success. We assessed for quality either observational or experimental studies.

Results

We identified 14 studies that met the inclusion criteria using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart with 12 observational and 2 experimental studies. Of 1691 DR-TB patients enrolled in the included studies, 1407 of them concomitantly received regimens containing bedaquiline and delamanid. Overall multidrug resistant (MDR), preextensively drug resistant (XDR), and XDR-TB were seen in 21.4%, 44.1%, and 34.5%, respectively. Of 14 studies, 8 of them reported favorable outcomes including sputum culture conversion and cure rate at the end of treatment, meanwhile 6 studies only reported sputum culture conversion. Sputum culture conversion at the end of the 6^th month was 63.6%-94.7% for observational studies, and 87.6%-95.0% for experimental studies. The favorable outcome at the end of treatment was 67.5%-91.4%. With high pre-XDR and XDR cases among DR-TB patients with limited treatment options, regimens containing bedaquiline and delamanid provide successful treatment.

Conclusion

In DR-TB patients receiving regimens containing bedaquiline and delamanid, favorable outcomes were high including sputum conversion and cure rate.

Systematic review with network meta-analysis on the treatments for latent tuberculosis infection in children and adolescents

BACKGROUND

We aimed to synthesize the evidence on the efficacy and safety of different treatment regimens for latent tuberculosis infection (LTBI) in children and adolescents.

METHODS

A systematic review with network meta-analysis was performed (CRD142933). Searches were conducted in Pubmed and Scopus (Nov-2021). Randomized controlled trials comparing treatments for LTBI (patients up to 15 years), and reporting data on the incidence of the disease, death or adverse events were included. Networks using the Bayesian framework were built for each outcome of interest. Results were reported as odds ratio (OR) with 95% credibility intervals (CrI). Rank probabilities were calculated via the surface under the cumulative ranking analysis (SUCRA) (Addis-v.1.16.8). GRADE approach was used to rate evidence's certainty.

RESULTS

Seven trials (n = 8696 patients) were included. Placebo was significantly associated with a higher incidence of tuberculosis compared to all active therapies. Combinations of isoniazid (15-25 mg/kg/week) plus rifapentine (300-900 mg/week), followed by isoniazid plus rifampicin (10 mg/kg/day) were ranked as best approaches with lower probabilities of disease incidence (10% and 19.5%, respectively in SUCRA) and death (20%). Higher doses of isoniazid monotherapy were significantly associated to more deaths (OR 18.28, 95% ICr [1.02, 48.60] of 4-6 mg/kg/day vs. 10 mg/kg/3x per week).

CONCLUSIONS

Combined therapies of isoniazid plus rifapentine or rifampicin for short-term periods should be used as the first-line approach for treating LTBI in children and adolescents. The use of long-term isoniazid as monotherapy and at higher doses should be avoided for this population.

The Struggle to End a Millennia-Long Pandemic: Novel Candidate and Repurposed Drugs for the Treatment of Tuberculosis

This article provides an encompassing review of the current pipeline of putative and developed treatments for tuberculosis, including multidrug-resistant strains. The review has organized each compound according to its site of activity. To provide context, mention of drugs within current recommended treatment regimens is made, thereafter followed by discussion on recently developed and upcoming molecules at established and novel targets. The review is designed to provide a clinically applicable understanding of the compounds that are deemed most currently relevant, including those already under clinical study and those that have shown promising pre-clinical results. An extensive review of the efficacy and safety data for key contemporary drugs already incorporated into treatment regimens, such as bedaquiline, pretomanid, and linezolid, is provided. The three levels of the bacterial cell wall (mycolic acid, arabinogalactan, and peptidoglycan layers) are highlighted and important compounds designed to target each layer are delineated. Amongst others, the highly optimistic and potent anti-mycobacterial activity of agents such as BTZ-043, PBTZ 169, and OPC-167832 are emphasized. The evolving spectrum of oxazolidinones, such as sutezolid, delpazolid, and TBI-223, all aiming to exceed the efficacy achieved with linezolid yet offer a safer alternative to the potential toxicity, are reviewed. New and exciting prospective agents with novel mechanisms of impact against TB, including 3-aminomethyl benzoxaboroles and telacebec, are underscored. We describe new diaryloquinolines in development, striving to build on the immense success of bedaquiline. Finally, we discuss some of these compounds that have shown encouraging additive or synergistic benefit when used in combination, providing some promise for the future in treating this ancient scourge.

Selection bias in multidrug-resistant tuberculosis cohort studies assessing sputum culture conversion

BACKGROUND

Conversion of sputum culture from positive to negative for M. tuberculosis is a key indicator of treatment response. An initial positive culture is a pre-requisite to observe conversion. Consequently, patients with a missing or negative initial culture are excluded from analyses of conversion outcomes. To identify the initial, or "baseline" culture, researchers must define a sample collection interval. An interval extending past treatment initiation can increase sample size but may introduce selection bias because patients without a positive pre-treatment culture must survive and remain in care to have a culture in the post-treatment interval.

METHODS

We used simulated data and data from the endTB observational cohort to investigate the potential for bias when extending baseline culture intervals past treatment initiation. We evaluated bias in the proportion with six-month conversion.

RESULTS

In simulation studies, the potential for bias depended on the proportion of patients missing a pre-treatment culture, proportion with conversion, proportion culture positive at treatment initiation, and proportion of patients missing a pre-treatment culture who would have been observed to be culture positive, had they had a culture. In observational data, the maximum potential for bias when reporting the proportion with conversion reached five percentage points in some sites.

CONCLUSION

Extending the allowable baseline interval past treatment initiation may introduce selection bias. If investigators choose to extend the baseline collection interval past treatment initiation, the proportion missing a pre-treatment culture and the number of deaths and losses to follow up during the post-treatment allowable interval should be clearly enumerated.

Insignificant difference in culture conversion between bedaquiline-containing and bedaquiline-free all-oral short regimens for multidrug-resistant tuberculosis

BACKGROUND

Multidrug-resistant tuberculosis (MDR-TB) patients have been suffering long, ineffective, and toxic treatment until short-course injectable-free regimens emerged. However, the new WHO-recommended regimens might be less feasible in the real-world setting. Here, we evaluated two optimized all-oral short-course regimens in China.

METHODS

From April 2019 to August 2020, we conducted a prospective nonrandomized controlled trial and consecutively included 103 MDR-TB patients diagnosed with pulmonary MDR-TB in Shenzhen, China. A 4-5 drug regimen of 9-12 months was tailored to the strain's resistance patterns, patients' affordability, and tolerance to drugs. This was an interim analysis, focusing on the early treatment period.

RESULTS

53.4% (55/103) of patients were prescribed linezolid, fluoroquinolone (FQ), clofazimine, cycloserine, and pyrazinamide, followed by a regimen in which clofazimine was replaced by bedaquiline (35/103, 34.0%). The culture conversion rate was 83.1% and 94.4% at two and four months, respectively, with no significant difference between bedaquiline-free and bedaquiline-containing cases and between FQ-susceptible and FQ-resistant cases. Among 41 patients who completed treatment, 40 (97.6%) patients had a favorable outcome and no relapse was observed. Peripheral neuropathy and arthralgia/myalgia were the most frequent AEs (56.3%, 58/103). 18 AEs caused permanent discontinuation of drugs, mostly due to pyrazinamide and linezolid.

CONCLUSION

Optimized all-oral short-course regimens showed satisfactory efficacy and safety in early treatment stage. Further research is needed to confirm these results.

Pretomanid with bedaquiline and linezolid for drug-resistant TB: a comparison of prospective cohorts

BACKGROUND: There are no data comparing the 6-9 month oral three-drug Nix regimen (bedaquiline, pretomanid and linezolid [BPaL]) to conventional regimens containing bedaquiline (B, BDQ) and linezolid (L, LZD).METHODS: Six-month post end-of-treatment outcomes were compared between Nix-TB (n = 109) and 102 prospectively recruited extensively drug-resistant TB patients who received an ˜18-month BDQ-based regimen (median of 8 drugs). A subset of patients received BDQ and LZD (n = 86), and a subgroup of these (n = 75) served as individually matched controls in a pairwise comparison to determine differences in regimen efficacy.RESULTS: Favourable outcomes (%) were significantly better with BPaL than with the B-L-based combination regimen (98/109, 89.9% vs. 56/86, 65.1%; adjusted relative risk ratio [aRRR] 1.35; P < 0.001) and in the matched pairwise analysis (67/75, 89.3% vs. 48/75, 64.0%; aRRR 1.39; P = 0.001), despite significantly higher baseline bacterial load and prior second-line drug exposure in the BPaL cohort. Time to culture conversion (P < 0.001), time to unfavourable outcome (P < 0.01) and time to death (P < 0.03) were significantly better or lower with BPaL than the B-L-based combinations.CONCLUSION: The BPaL regimen (and hence substitution of multiple other drugs by pretomanid and/or higher starting-dose LZD) may improve outcomes in drug-resistant TB patients with poor prognostic features. However, prospective controlled studies are required to definitively answer this question.

On the relationship between association and surrogacy when both the surrogate and true endpoint are binary outcomes

The relationship between association and surrogacy has been the focus of much debate in the surrogate marker literature. Recently, the individual causal association (ICA) has been introduced as a metric of surrogacy in the causal inference framework, when both the surrogate and the true endpoint are normally distributed and when both are binary. Earlier work on the normal case has demonstrated that, although the ICA and the adjusted association are related metrics, their relationship strongly depends on unidentifiable parameters and, consequently, the association between both endpoints conveys little information on the validity of the surrogate. In addition, in the normal setting, the magnitude of the ICA does not depend on the mean of the outcomes. The latter implies that identifiable parameters such as mean responses and treatment effects provide no information on the validity of the surrogate. In the present work it is shown that this is fundamentally different in the binary case. We demonstrate that the observed association between the outcomes as well as the success rates in both treatment groups are quite predictive for the ICA. It is shown that finding a good surrogate will be more likely when the association between the endpoints is large, there are sizeable treatment effects and the success rates for both endpoints are similar in both treatment groups. These results are demonstrated using extensive simulations and illustrated on a case study in multi-drug resistant tuberculosis.