Pharmacokinetics and Pharmacodynamics of the Etonogestrel Contraceptive Implant When Co-administered With Efavirenz

Women now make up nearly half of the world's HIV-infected population, and many of these women with HIV are of reproductive age. There is a growing need to provide effective contraception for those women who want or need to be protected against pregnancy. However, there is concern for decreased contraceptive efficacy in women on antiretroviral therapy who rely on hormonal contraception due to drug-drug interactions. Of particular concern is a possible interaction with etonogestrel, the active hormone in a long-acting reversible contraceptive implant. We propose a pilot study to evaluate the effect of efavirenz (EFV), a commonly used non-nucleoside reverse transcriptase inhibitor, on the pharmacokinetics of the etonogestrel implant. We will recruit 18 healthy women who have had the implant in place for 12 to 24 months. They will be asked to take a two-week course of efavirenz. During these two weeks and for four additional weeks, we will monitor semi-weekly etonogestrel concentrations, and serum, ultrasound, and cervical mucus markers of ovulation. We will also assess efavirenz concentration at baseline and at the end of the two-week treatment course. We will derive pharmacokinetic parameters and compare concentrations across time points. Results will help to inform the design of larger studies, and of similar studies with different antiretroviral medications. We hypothesize that taking efavirenz while using the etonogestrel contraceptive implant will not result in an increased incidence of ovulation.