Background: The optimal dosing strategy for rifampicin in treating drug-susceptible tuberculosis (TB) is still highly debated. In the Phase 3 clinical trial Study 31/ACTG 5349 (NCT02410772), all participants in the control regimen arm received 600 mg rifampicin daily as a flat dose. Here, we evaluated relationships between rifampicin exposure and efficacy and safety outcomes.
Methods: We analyzed rifampicin concentration time profiles using population nonlinear mixed-effects models. We compared simulated rifampicin exposure from flat- and weight-banded dosing. We evaluated the effect of rifampicin exposure on stable culture conversion at 6 months, TB-related unfavorable outcomes at 9, 12, and 18 months using Cox proportional hazard models, and all trial-defined safety outcomes using logistic regression.
Results: Our model derived rifampicin exposure ranged from 4.57 mg·h/L to 140.0 mg·h/L with a median of 41.8 mg·h/L. Pharmacokinetic simulations demonstrated that flat-dosed rifampicin provided exposure coverage similar to weight-banded dose. Exposure-efficacy analysis (N=680) showed that participants with rifampicin exposure below the median experienced similar hazards of stable culture conversion and TB-related unfavorable outcomes compared to those with exposure above the median. Exposure-safety analysis (N=722) showed that increased rifampicin exposure was not associated with increased grade 3 or higher adverse events, or serious adverse events.
Conclusions: Flat-dosing of rifampicin at 600 mg daily may be a reasonable alternative to the incumbent weight-banded dosing strategy for the standard of care 6-month regimen. Future research should assess the optimal dosing strategy for rifampicin, at doses higher than the current recommendation.
Keywords: dose optimization; flat-dosing; population pharmacokinetics; rifampicin; tuberculosis; weight-banded dosing.
© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America.