A vaginal microbicide gel containing the red seaweed extract carrageenan is one of the most promising of several microbicide candidates to be discussed at Microbicides 2002 (May 12-15; Antwerp, Belgium). The gel, known as carraguard, has already been shown to block HIV and other STDs in vitro. Now researchers from the Population Council, a non-profit research organization, plan to test the gel's efficacy as a vaginal microbicide in 6,000 non- pregnant, HIV-negative women in South Africa and Botswana. The participants will receive carraguard, placebo control, or condoms alone.

The phase III trial is expected to start in early 2003 and will follow the women for two years. "The vast majority of the current 60 or so microbicide products in the pipeline are still being tested in the laboratory and only a handful, maybe one- quarter, are in phase I/II safety testing," said Janneke van de Wijgert, lead investigator for the phase III trial.

The team has already done a phase II safety trial investigating the use of carraguard among 565 women in South Africa and Thailand. These data are currently undergoing analysis and results are expected by the end of 2002. Preliminary, blinded data from the trial reported, "very few safety endpoints that were statistically significantly different from the placebo arm," van de Wijgert said. "We had some adverse events but they were all the usual things: a lot of cold, headache, and flu," she added. "We don't think they were related to gel use."

Laboratory studies have found that carraguard blocked HIV, herpesvirus, human papillomavirus, and gonorrhea in vitro. In many studies in mice, it protected animals against herpesvirus, and was "significantly protective" against human papillomavirus and gonorrhea infection, according to the Population Council's David Phillips, a co-investigator on one of the mouse studies.

Stability testing has shown that carraguard has a shelf life of at least two years, and preclinical tests show the product is well tolerated and non-irritating. These features, Phillips suggests, could give the compound an edge over other candidate microbicides. "When you develop a product, healthy people have to be able to use it for an extended period of time, maybe a year. Carraguard happens to be very stable and safe, and I am not sure the other candidates are going to be," explained Phillips.

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