An anti-HIV vaginal gel did not meet expectations during human trials.
The anti-HIV gel called PRO 2000 contains a polymer of naphthalene sulphonate designed to physically prevent HIV from binding to cells lining the vagina. Women were given condoms to use in conjunction with it.
A smaller trial conducted in February appeared to lower the risk of infection by 30 per cent, but in larger trials the gel failed to show promising results.
The researchers found that of 3156 women who used the active gel in Uganda, Zambia, Tanzania and South Africa, 4.1 per cent became infected, versus 4.0 per cent of the 3112 users of the placebo.
"It very clearly doesn't work," New Scientist quoted chief investigator Sheena McCormack, of the MRC as saying.
"It tells us that the level of biological potency is not enough," she added.
On possible reason for its failure might be that the gel didn't perfectly cover vaginal surfaces, providing chinks for the virus to get through, said McCormack.
Another reason could be, she said, is that the active substance in the gel simply wasn't potent enough at blocking HIV.
McCormack added increasing its concentration, however, would make the gel impractically viscous.
"It's time to give up on this type of chemical, but not on the idea," said McCormack.