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LONDON (Reuters) - U.S. drug firm Endo Pharmaceuticals' gel designed to prevent infection with the AIDS virus has proved ineffective in trials in Africa, Britain's Medical Research Council (MRC) said on Monday.

A large international trial of vaginal microbicide Pro 2000 in more than 9,000 women in four African countries found no evidence that it reduces the risk of HIV infection.

The result is a setback for the specialty drugmaker, whose shares were hit earlier in the month when U.S. health regulators declined to approve its Aveed drug for low testosterone.

To date, no gel microbicide has been shown to work against HIV infection and this trial "showed conclusively that Pro 2000 gel was of no added benefit", the MRC said in a statement.

It said this would end scientific speculation about its clinical importance.

"This result is disheartening, particularly in light of the results of a smaller trial sponsored by the U.S. National Institutes of Health which suggested that Pro 2000 could reduce the risk of HIV infection by 30 per cent," said the MRC's Sheena McCormack, who led the trial.

"Nevertheless we know this is an important result and it shows clearly the need to undertake trials which are large enough to provide definitive evidence for whether or not a product works."

Studies presented at an AIDS conference in Canada in February suggested the Pro 200o gel, which ENDO acquired through its purchase of Indevus Pharmaceuticals earlier this year, could cut transmission rates by a third .