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Background: Tachycardia associated with active tuberculosis (TB) often diminishes when patients recover from TB. Elevated heart rate (HR) may lead to suboptimal correction, complicating the assessment of QT prolongation when using standard correction factors (CFs), such as Fridericia's formula (QTcF). Olliaro has proposed a CF for QT interval correction in pretreatment TB patients. However, the QT-HR correlation changes as HR decreases during treatment, indicating the need for time-varying correction.

Methods: We developed an HR model to capture the HR normalisation during successful treatment. Subsequently, a time-varying CF was constructed using the estimated HR change rate. The performance of CFs to make corrected QT (QTc) independent from HR was evaluated by linear regression analyses of QTc versus HR within defined time bins.

Results: The final HR model included asymptotic change in HR attributed to time on treatment, circadian rhythm cycles, M2 (bedaquiline-metabolite) concentration, and patient covariates. The time-varying CF decreased from 0.4081 to 0.33, with a half-life of 7.74 weeks. The slope (QTc/HR vs. Time) derived from the time-varying correction was not significantly different from 0 (95% CI -0.003 to 0.002), and the intercept was not significantly different from 0 (95% CI -0.089 to 0.006), demonstrating successful QT correction from pretreatment to the end of treatment.

Conclusion: The time-varying CF effectively captures the dynamic QT-HR relationship during TB treatment, reducing the risk of misdiagnosing QT prolongation or unnecessary discontinuation of treatment. By addressing underestimation and overestimation issues in QT interval assessment, this method enhances drug evaluation in clinical trials and supports improved treatment decisions for TB patients. (c) 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Evaluating QT prolongation induced by anti-tuberculosis (TB) drugs in patients with active TB, who often experience tachycardia, is challenging due to the limitations of Fridericia's correction factor (QTcF) in decorrelating QTc from heart rate (HR). Previous exposure-QTcF analyses in patients with active TB were able to alleviate the limitation of QTcF but required advanced model-based methodologies, incorporating a non-drug-related, "secular" trend in the model to dissociate drug and non-drug-related effects on QT. Recently, we developed and validated a time-varying QT correction method (QTcTBT) that more accurately accounts for the HR changes during TB treatment. In the present work, using data from 429 patients with multidrug-resistant TB across two Phase IIb trials, we re-evaluated the exposure-QTc relationship for bedaquiline by applying QTcTBT instead of QTcF. Our analysis showed that when HR changes were accounted for using QTcTBT, a typical maximum M2 (bedaquiline metabolite) concentration (326 ng/mL, mean maximal concentration (Cmax) at the end of 2-week loading phase) was associated with a 7 ms QTc interval prolongation (90% CI: 5.9-8.2). This estimate closely aligns with the previously reported M2 effect of 7.9 ms (90% CI: 6.8-9.3), derived from the exposure-QTcF model. The consistency between the two methodologies further supports the use of QTcTBT for estimating the QTc prolongation effects of anti-TB drugs.

Background and Objectives

The use of the 12-dose, once-weekly, rifapentine-based (3HP), short-course tuberculosis preventive treatment (TPT) in children has been limited due to a lack of child-friendly rifapentine formulations. In this study, we compared the relative bioavailability of rifapentine and isoniazid when suspended in water versus whole tablets, using generic adult formulations.

Methods

We assessed the relative bioavailability of non-dispersible rifapentine and isoniazid adult tablets suspended in water compared with whole tablets. Adults with a positive tuberculosis infection test were randomized 1:1:1 to receive two of three rifapentine/isoniazid formulations in separate treatment sequences, including two generic brands of fixed-dose combinations and standalone tablets of rifapentine and isoniazid. Participants received either whole tablets swallowed or tablets suspended in water at a dose of 900 mg for each drug once weekly over 12 weeks with intensive pharmacokinetic sampling up to 48 h post-dose. Nonlinear mixed-effects modelling was used to compare the relative bioavailability of suspended versus whole tablets, with 90% confidence intervals (CI) evaluated against the standard bioequivalence range (80–125%).

Results

In 24 participants, a one-compartment model described rifapentine data well. A two-compartment model with a mixture component for fast/intermediate and slow acetylators best described isoniazid. Rifapentine and isoniazid demonstrated similar bioavailability across all dosing forms, meeting formal bioequivalence criteria. The absorption rates for suspended tablets were faster than those for whole tablets by 22.2% (90% CI 12.4–30.8) for rifapentine and 35% (90% CI 26.1–42.6) for isoniazid.

Conclusion

Both rifapentine and isoniazid, whether in fixed-dose combinations or as standalone, showed similar bioavailability when administered as whole tablets or suspended in water. These findings support dosing in children and other populations without the need to adjust rifapentine or isoniazid doses, thereby supporting broader access to the 3HP regimen.

Pan African Clinical Trials Registry

PACTR202306775627089, registration date June 15, 2023.