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Case 4: Antiretrovirals and Oral Contraceptives

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A Efavirenz (Sustiva) will likely reduce the efficacy of the oral contraceptive pill.

This answer is correct. The major biotransformation of ethinyl estradiol is through the 3A4 cytochrome pathway. Efavirenz is a known inducer of 3A4 and thus would be expected to lower ethinyl estradiol levels. Available data, however, show that efavirenz does not significantly alter ethinyl estradiol levels. In contrast, efavirenz has been shown to significantly lower levels of norelgestromin and levonorgestrel (active metabolites of norgestimate) and thus efavirenz would be expected to lower the levels of other progestins, such as norethindrone. Accordingly, it is recommended that patients taking efavirenz should use alternative or additional birth control measures. If a woman was taking an oral contraceptives and efavirenz and became pregnant, this would be highly undesirable, given the potential first trimester tetatogenicity associated with efavirenz.

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