Unintended Pregnancies Observed With Combined Use of the Levonorgestrel Contraceptive Implant and Efavirenz-based Antiretroviral Therapy: A Three-Arm Pharmacokinetic Evaluation Over 48 Weeks

Women receiving efavirenz-based antiretroviral therapy plus a contraceptive implant had significantly lower levonorgestrel pharmacokinetics than women not receiving antiretroviral therapy. An unexpected high pregnancy rate (3/20, 15%) occurred in the efavirenz group, highlighting the clinical significance of this interaction.
Background. Levonorgestrel subdermal implants are preferred contraceptives with an expected failure rate of