A U. S. drug company Endo Pharmaceuticals' (ENDP. O) gel designed to prevent AIDS virus was ineffective in trials in Africa, Britain's Medical Research Council (MRC) said on Monday.

Researchers said the failure was the last nail in the coffin for this type of microbicide — gels containing molecules that bundle around the virus before it reaches the vaginal wall. Attention is now turning to gels and rings that release constant doses of antiretroviral drugs to kill the virus or stop it from reproducing.

The large international trial of vaginal microbicide Pro 2000 recruited women in South Africa, Zambia, Uganda and Tanzania. Some were from the general population, some worked at highway truck stops, and some were not infected but married to men who were. The results found no evidence that it helps reduce HIV infection.

“It is bitterly disappointing for us, but it will inform the way we go forward,” Dr Sheena McCormack, the trial’s chief investigator, said.

Microbicide Pro 2000 worked nearly perfectly on cells in the laboratory and in monkeys.

Researchers are beginning to test gels and rings containing antiretroviral drugs like tenofovir, dapivirine and maraviroc.

Mitchell Warren, executive director of AVAC, an advocacy group for AIDS vaccines, microbicides and other means for blocking the disease, called the results unacceptable.

"It is unfortunate that this microbicide is ineffective at preventing HIV infection but it's still vital for us as scientists to continue to look for new ways of preventing HIV," Jonathan Weber from MDP said in a statement.