Effect of high-dose rifampicin on efavirenz pharmacokinetics: drug-drug interaction randomized trial.

Background: High-dose rifampicin is considered to shorten anti-TB treatment duration but its effect on antiretroviral metabolism is unknown. Objectives: To assess the effect of doubling the rifampicin dose (to 20mg/kg/day, R20) on efavirenz pharmacokinetics (PK) in HIV/TB coinfected patients. Methods: Open-label Phase 2 drug-drug interaction randomized trial. Pulmonary TB, ART-naive adults were randomized to R20 and either efavirenz 600mg (EFV600) or 800mg (EFV800), or rifampicin 10mg/kg/day (R10) and EFV600 with a 1:1:1 ratio. Patients were first started on TB treatment and 2-4weeks later started on ART. They were switched to R10 and EFV600 after 8weeks. Full PK sampling was done 4weeks (on rifampicin) and 24weeks (off rifampicin) after ART initiation. Transaminases, plasma HIV-1 RNA and sputum cultures were monitored. The efavirenz geometric mean ratio (GMR) of AUC at 4 and 24weeks after ART initiation within the same patient was calculated in each arm and its 90% CI was compared with a preset range (0.70-1.43). Results: Of 98 enrolled patients (32 in the R20EFV600 arm, 33 in the R20EFV800 arm and 33 in the R10EFV600 arm), 87 had full PK sampling. For the R20EFV600, R20EFV800 and R10EFV600 arms, GMRs of efavirenz AUC were 0.87 (90% CI: 0.75-1.00), 1.12 (90% CI: 0.96-1.30) and 0.96 (90% CI: 0.84-1.10). Twelve weeks after ART initiation, 78.6%, 77.4% and 72.4% of patients had HIV-1 RNA below 100copies/mL and 85.7%, 86.7% and 80.0% had Week 8 culture conversion, respectively. Two patients per arm experienced a severe increase in transaminases. Conclusions: Doubling the rifampicin dose had a small effect on efavirenz concentrations and was well tolerated.