Kampala — Researchers have initiated studies to establish whether antiretroviral drugs can effectively be used to block HIV infection. Scheduled to end at the close of next year, the study is now recruiting participants and will initially start in the US, with additional sites soon opening in Uganda and South Africa.

According to the Microbicide Trials Network (MTN), the ARV drug tenofovir has particular promise because it can be formulated as either an oral tablet or a vaginal gel to be used daily. This will be the first clinical trial to directly compare the tablet and vaginal gel formulations of tenofovir, amid scientific and practical challenges.

A statement issued last week by MTN notes that because certain cells in the vagina are easy targets for the virus, women are more than twice as likely as their male partners to acquire HIV through sexual intercourse.

As such, "the clinical study, known as MTN-001, seeks to understand how each formulation of tenofovir works in these infection-prone cells, information that will help researchers determine the optimal doses needed to achieve drug concentrations most likely to prevent HIV in women."

This development comes at a time when HIV prevention efforts have suffered serious blows over the last one year that saw two promising trials of candidate microbicides and vaccines stopped. In early 2007, a trial of the gel meant to prevent HIV infection in women was prematurely called off after researchers found that it did not protect the women from infection.

Then late 2007 saw the stoppage of the vaccine trial because although the candidate vaccine did not cause any infections, it made participants vulnerable to HIV infection.

This has since led to writing off of another vaccine trial dubbed PAVE 100 in which Ugandan participants were to be enrolled. However, the Principal Investigator of the IAVI (International Aids Vaccine Initiative Vaccine) Programme in Uganda Dr Pontiano Kaleebu said on Tuesday that all was not lost.

"We are just being cautious. The large scale studies will not be done, but what is going to happen is that smaller PAVE 100 trials will go on in the US," Dr Kaleebu said. "And there are several other vaccine trials going on around the world involving different vaccines. So the search is still on."

An estimated one million people are living with HIV/Aids in Uganda while hundreds get infected every year, according to Health officials.