The Population Council, a nonprofit research organization, which has been developing the microbicide Carraguard, announced today that phase III clinical results show it ineffective in preventing HIV transmission.

The trial, which ended in March of last year, involved 6,202 women and cost around $40 million. Of the 3,103 participants who were using the microbicide gel, 134 became infected with the virus while on the trial, as opposed to 151 out of 3,099 who were using a placebo. These results are not statistically significant, Khatija Ahmed, from the University of Limpopo in South Africa, and principal investigator of the trial, said in a telephone press conference last Thursday (February 14).

Microbicides to prevent HIV have had a rough ride on the path to development, and there are currently none approved for use as anti-HIV agents. Last year, the phase III clinical trial for an anti-HIV microbicide called Ushercell was halted when initial data suggested that it increased the risk for infection.

Carraguard is a clear gel that, when applied to the vagina, is supposed to block pathogens from reaching epithelium cells.

But the Carraguard results won't put an end to microbicide development, Robin Maguire, director of microbicides product development at the Population Council's Center for Biomedical Research, said during the press conference call. "We will be developing the next generation of products using Carraguard; this study did demonstrate its safety," she said. In particular, the organization is hoping to start a phase I clinical trial this year of a microbicide that is a combination of Carraguard and an antiretroviral, MIV-150. In vitro testing has shown the antiretroviral to be more stable in the Carraguard gel than an inert gel.

Of all participants who enrolled in the trial about 69% completed it in full, and only about 10% used the gel 100% of the time. Researchers are continuing to analyze these results to determine if low adherence might have played into the efficacy results.