BOSTON – Efavirenz-based antiretroviral therapy may significantly impair the effectiveness of vaginal ring contraceptives, investigators reported.
Over a 21-day period, levels of estrogen among women who used a vaginal ring (NuvaRing) while on efavirenz-based antiretroviral therapy (ART) were up to 79% lower, and levels of progestin were up to 57% lower, than in women with HIV infection who used the vaginal ring before starting ART, reported Kimberly K. Scarsi, PharmD, of the University of Nebraska, Omaha.
In contrast, women on an atazanavir-based ART regimen had lower estrogen levels than untreated controls who used a vaginal ring, but higher levels of progestin – the primary antiovulatory component of the ring – suggesting that it would retain contraceptive effectiveness, she said at the annual Conference on Retroviruses and Opportunistic Infections.
“In a broader context, these data can be applied to other drugs that behave similarly. So for example, erythromycins are also known to interfere with hormones in this way, as well as some anticonvulsant agents that may also impair the effectiveness of vaginal ring contraceptives,” she said at a brief, following her presentation of the data in an oral abstract session.