Pharmacokinetics of dose-adjusted levonorgestrel emergency contraception combined with efavirenz-based antiretroviral therapy or rifampicin-containing tuberculosis regimens

OBJECTIVES: To determine if double-dose levonorgestrel emergency contraception (EC) in combination with efavirenz or rifampicin, 2 drugs known to decrease levonorgestrel exposure, resulted in similar pharmacokinetics compared to standard-dose levonorgestrel EC without drug-drug interactions. STUDY DESIGN: We conducted a phase 2, open-label, multicenter, partially randomized, 4 parallel group trial in pre-menopausal females ≥16 years old without an indication for EC and not on hormonal contraception. Participants on dolutegravir-based antiretroviral therapy (ART) received levonorgestrel 1.5 mg (control group); those on rifampicin-containing tuberculosis therapy received levonorgestrel 3 mg; those on efavirenz-based ART were randomized 1:2 to levonorgestrel 1.5 mg or 3 mg. Plasma was collected through 48 hours post-dose to assess levonorgestrel pharmacokinetics. Area under the concentration-time curve (AUC) over 8 hours was the primary outcome. Levonorgestrel pharmacokinetic parameters were compared between groups using geometric mean ratios (GMR) with 90% confidence intervals. RESULTS: when receiving either efavirenz (n = 35) [0.99 (0.81, 1.20)] or rifampicin (n = 34) [1.16 (0.99, 1.36)] compared to control. Levonorgestrel 3 mg resulted in similar or higher maximum concentration with either efavirenz [1.17 (0.96, 1.41)] or rifampicin [1.27 (1.09, 1.49)] compared to the control group. CONCLUSIONS: Doubling the dose of levonorgestrel EC successfully increased levonorgestrel exposure over the first 8 hours in participants receiving either efavirenz-based ART or rifampicin-containing tuberculosis therapy. IMPLICATIONS: Adjusting levonorgestrel emergency contraception from 1.5 mg to 3 mg improves levonorgestrel pharmacokinetic exposure in participants receiving either efavirenz-based antiretroviral regimens or rifampicin-containing tuberculosis therapy. These data support guideline recommendations to double the dose of levonorgestrel emergency contraception in persons on medications that decrease levonorgestrel exposure by inducing levonorgestrel metabolism.