A gel made by US drug firm Endo Pharmaceuticals that is designed to prevent infection with the AIDS virus has proved ineffective in trials in Africa, Britain's Medical Research Council said today.

A large international trial of the 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.

To date no gel microbicide has been shown to be effective against HIV infection and this trial showed conclusively that PRO 2000 gel was of no added benefit, ending scientific speculation about its clinical importance, the MRC said in a statement.

"This result is disheartening, particularly in light of the results of a smaller trial sponsored by the US National Institutes of Health (NIH) which suggested that PRO 2000 could reduce the risk of HIV infection by 30 per cent," said Sheena McCormack of the Medical Research Council, 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."

The MRC's trial was the largest international clinical trial to date into a preventative HIV gel. It took place between September 2005 and September 2009 involved 9,385 women and was carried out by the Microbicides Development Programme, a not-for-profit partnership of 16 African and European research institutions.

The trial found that the risk of HIV infection in women who were given PRO 2000 gel was not significantly different than in women supplied with a placebo gel.

Jonathan Weber of the MDP said the result was disappointing but added: "The trial itself was very well designed and undertaken, so we know that the results are definitive.

"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," he said in a statement.