CAPE TOWN - Hopes that the microbicide Pro 2000 might block transmission of HIV have been dashed, after results from a large study sponsored by the UK's Medical Research Council had shown it offered women no protection against the virus.

Microbicides are gels, creams or foams that are inserted into the vagina or rectum. So far, every product tested has either done nothing, or increased the risk of infection.

"It's disappointing. But the hunt for a microbicide is not something we will give up on," said the study's principal investigator for the Durban site, Gita Ramjee.

But the latest setback means researchers will close the door on what are known as second generation products such as Pro 2000 and turn to more promising products. These includ e tried and tested antiretroviral drugs already on the market for HIV/AIDS patients.

Researchers hope a safe and effective microbicide will give women more options for protecting themselves from infection from HIV, particularly when men are loath to use condoms. A microbicide could also be useful for women who are trying to fall pregnant, as the products tested so far do not affect conception.

In February, another Pro 2000 trial suggested it might reduce the risk of getting HIV by 30%, but the small size of the trial meant the findings were not statistically significant. Scientists could not be sure whether slightly fewer gel users than non-users getting HIV meant the product really did prevent HIV transmission or that it was due to chance.