Disappointing study results showed that precoital vaginal gel containing tenofovir does not prevent HIV acquisition in women, in part because of poor adherence during the clinical trial.
A vaginal gel developed to prevent sexual transmission of HIV between men and women was not effective in a clinical trial, according to results presented at the 2015 Conference on Retroviruses and Opportunistic Infections held in Seattle, WA.
The gel containing the drug tenofovir had shown promising results in an earlier, proof-of-concept trial. However, this latest Phase 3 clinical trial failed because women did not correctly use the pericoital vaginal gel, according to the study abstract.
The double-blind, randomized, placebo-controlled trial tested the gel in nine centers in South Africa. The purpose of the study was to evaluate the safety and effectiveness of the pericoital tenofovir 1% gel when used before and after sex for no more than two doses in 24 hours, according to the abstract.
The study involved HIV-negative women between the ages of 18 to 30 who were given intensive counselling on the proper use of the product, how to reduce the risk of HIV infection and condom provision, the abstract states. Researchers held monthly follow-up visits with participants that included HIV and safety testing and the return of unused product and used applicators.
Counselling on product adherence continued for up to 27 months. Adherence was measured by how often the gel was used during self-reported sex acts.
Out of 3844 people screened for the study from October 2011 to August 2014, there were 2059 enrolled and 2029 included in the primary analysis. A typical participant was about 23 years old, unmarried, lived with her parents, and had earned about $100 in the previous three months.
The drug failed to meet its target and prevent the spread of HIV mainly because the young women did not apply the gel as instructed. Study results indicate that overall there were 123 HIV infections, split almost evenly between the study drug and placebo groups, 61 and 62 respectively.
The tenofovir gel was most effective among women who reported using the product for 72% of sex acts but these women were only 20% of study participants, according to the study abstract.
The study authors concluded that the pericoital vaginal tenofovir 1% gel did not effectively prevent HIV. An analysis of data found an association between adherence based on returned applicators and HIV effectiveness, the abstract states.