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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.
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