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A single-arm pharmacokinetic study investigated the interaction of efavirenz and levonorgestrel. HIV-seronegative women were given a single dose (0.75 mg) of levonorgestrel both before and after they had received efavirenz 600 mg daily for 14 days. Coadministration of efavirenz with levonorgestrel resulted in a 58% decrease in the levonorgestrel AUC and a 69% decrease in C_min. Efavirenz levels were not different than those in a historical comparator.

Clinical Bottom Line

Efavirenz significantly decreases levonorgestrel levels. Pending the results of clinical studies, an additional or alternative form of birth control (or emergency contraception [Plan B]) should be used for women who take efavirenz.

For more information on interactions between ARVs and hormonal contraceptives, see HIV InSite's Database of Antiretroviral Drug Interactions.

References

Carten M, Kiser J, Kwara A, et al. Pharmacokinetic interactions between the hormonal emergency contraception, levonorgestrel, and efavirenz. In: Program and abstracts of the 17th Conference on Retroviruses and Opportunistic Infections; February 16-19, 2010; San Francisco. Abstract 934.