Two more clinical trials will be conducted in Africa to determine whether the protective effects of a tenofovir-based vaginal gel against HIV infection can be replicated in different populations of women and with a different dosing schedule.

The trials with the microbicide gel containing Gilead Sciences’ antiretroviral tenofovir, marketed as Viread for the treatment of chronic hepatitis B and Human Immunodeficiency Virus 1 (HIV-1) infection, were proposed at a meeting convened in Johannesburg, South Africa last week by UNAIDS (the Joint United Nations Programme on HIV/AIDS) and the World Health Organization (WHO).

The meeting brought together representatives of government agencies and national drug regulatory authorities, microbicide research teams and product developers, women’s health and HIV prevention advocates, people with HIV, clinical and social science researchers, statisticians, civil society representatives, public health experts and ethicists. They agreed a road map for further development of the tenofovir gel following the impressive results from the CAPRISA 004 study reported at the XVIII International AIDS Conference in Vienna, Austria in July 2010.

Conducted by the Centre for the AIDS Programme of Research in South Africa (CAPRISA), a UNAIDS collaborating centre for HIV prevention research, the CAPRISA 004 trial involved 889 women at high risk of HIV infection in KwaZulu-Natal. It found that a vaginal gel containing 1% tenofovir was 39% effective at reducing a woman's risk of becoming infected with HIV during sex, as well as 51% effective at preventing genital herpes infections.

One of the confirmatory trials, to be conducted mainly in South Africa, will look at whether the CAPRISA results can be replicated in a variety of settings with a population that includes younger women, UNAIDS said. It will also assess whether the gel can be used safely by sexually active 16 and 17 year-olds in settings where HIV incidence is high.

A second trial, which will take place in other African countries, will evaluate the safety and efficacy of a different dosing schedule. It will examine whether a single application of the tenofovir gel before sex – or, failing that, immediately after sex – is as safe and effective as the original two-dose regimen. A single-dose schedule would be less expensive and easier for women to use, UNAIDS noted.

An ongoing trial being conducted by the Microbicides Trial Network, which is evaluating the same gel used daily, will generate additional data on safety and product use. Research in the communities where the CAPRISA 004 trial was carried out will look at how to best promote, distribute and monitor gel use through existing family planning facilities. 

While participants at the meeting in Johannesburg agreed on research priorities for the tenofovir gel, concerns were expressed over the limited funding committed so far to carry forward the next phase of research. The next steps are expected to cost US$100 million, while at present only US$58 million is available for the programme, UNAIDS pointed out.