Study: In two-drug, HIV-preventing vaginal ring, only one drug does the job

The National Institutes of Health has shown that a study of its vaginal ring for the prevention of HIV came back with mixed results. The ring, which delivers two drugs, was safe for 28 days, but only one of the antiretroviral drugs was effective in protecting against the virus.

The Phase I study, performed by the Microbicide Trials Network, who announced the results at the 21st Conference on Retroviruses and Opportunistic Infections this week in Boston, was the first study to examine the delivery of two different drugs as a measure against HIV.

The microbicides used in the vaginal ring are dapivirine, which demonstrated effectiveness by appearing in cervical tissue and blood, and maraviroc, which didn't have the same effect.

"It's encouraging that both drugs were safe, and that most women didn't mind wearing the ring," said presenter Beatrice Chen of the University of Pittsburgh in a statement. "However, we found maraviroc wasn't getting absorbed in tissue like dapivirine was and it didn't work as well as dapivirine in our laboratory studies looking at activity against HIV."

Dapivirine alone is undergoing two Phase III trials in Africa. But with the combination trial, which in theory would provide more protection because the drugs act in different ways to prevent HIV, there's more work to do to make it effective.

The combination ring was worn by HIV-negative women between the ages of 18 and 40 for 28 days in the trial. The silicone elastomer rings, which are similar to those used for contraception, caused only mild side effects and were deemed comfortable. The women either wore the ring with the combination of drugs, one with either one of the drugs or one with no active substance.

The researchers collected samples of tissue during the trial, exposing them to the virus in the lab, noting that dapivirine protected the samples against infection. Tissue from women who wore only the maraviroc ring, however, showed very little of the drug and wasn't protected against HIV.

The nonprofit organization IPM is working with Viiv Healthcare to develop maraviroc, which has been approved for use in HIV treatment with other antiretroviral drugs. Dapivirine is being developed by IPM with Janssen R&D Ireland.

"As an entry inhibitor, maraviroc is a promising candidate for development as a microbicide for HIV prevention because it acts at a different step in the infectious process from other HIV prevention drugs," IPM CEO Zeda Rosenberg said in a statement. "IPM is conducting additional development work to increase the amount of maraviroc that gets into cervical tissue in order to best harness the drug's potential in the combination ring, and we are planning a second safety study for 2015."

- here's the Microbicide Trials Network announcement