The antiretroviral (ARV)-containing vaginal ring form of pre-exposure prophylaxis (PrEP) that reduced HIV risk in a major trial does not lower the effectiveness of hormonal birth control. This finding assuages concerns raised by previous research that the non-nucleoside reverse transcriptase inhibitor (NNRTI) class of ARVs has been associated with a lowered effectiveness of some hormonal contraceptives.

Results from the randomized, double-blind, placebo-controlled Phase III MTN-020/ASPIRE study of a vaginal ring containing the NNRTI dapivirine were presented at the 2016 Conference on Retroviruses and Opportunistic Infections (CROI) in Boston. The ring was modestly successful at reducing the risk of HIV among sexually active women in Malawi, South Africa, Uganda and Zimbabwe. Overall, those who received the drug-infused ring had a 27 percent lower HIV rate than those who received a placebo ring.

Further results presented at the 21st International AIDS Conference in Durban, South Africa, (AIDS 2016) showed that the highest level of adherence to the ring was associated with a 75 percent reduction in HIV risk.

Jennifer Balkus, PhD, of the Fred Hutchinson Cancer Research Center presented findings at the 2017 CROI in the center’s home city of Seattle of a subsequent analysis of ASPIRE to examine the vaginal ring’s effects on birth control effectiveness, presenting their findings at the

Participants in the study were required to use an effective form of contraception. When they came in for monthly visits, clinic workers would record their contraceptive method and conduct urine pregnancy tests. If a woman became pregnant, she was taken off the vaginal ring and not started on it again until she was no longer breast feeding.

Of 2,629 women enrolled in the trial, 2,310 returned for follow-up and reported using a highly effective contraceptive, including 1,139 randomized to receive the dapivirine-containing ring and 1,171 who were randomized to receive a placebo-containing ring. The women’s demographics were similar between the two study arms.

There were a total of 117 pregnancies among 114 of the women, including 63 pregnancies in the vaginal ring arm and 54 in the placebo arm.

Among women reporting use of injectable depot medroxyprogesterone acetate (DMPA), injectable norethisterone enanthate (NET-EN), hormonal implants and oral contraceptive pills, the respective pregnancy rates per year were 0.49 percent, 0.58 percent, 0.45 percent and 30.15 percent.

The study authors saw no difference in the pregnancy rate between the dapivirine and placebo arms of the trial, regardless of the form of birth control used.

Notably, while reported use of injectable and implantable contraceptives was highly effective at preventing pregnancy, reported use of oral contraceptives was associated with a high pregnancy rate. The investigators speculated that this was the result of poor adherence to the pill regimens.

Balkus told CROI that the topical use of the drug in the vaginal ring likely reduces the chance of drug-drug interactions with contraceptives administrated in other forms. That said, oral PrEP studies among women have also found no difference in efficacy of PrEP based on the use of birth control.