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GLOBAL: ARVs for prevention? Proceed with caution, say researchers
ARVs may soon be used to prevent, as well as to treat, HIV
Johannesburg, 25 May 2010 (IRIN) - Two new studies have confirmed fears that the use of antiretroviral (ARV) drugs to prevent HIV could lead to drug resistance if inadvertently used by people who were already infected.
The findings presented this week at the International Microbicides Conference in Pittsburgh, in the US, suggest that regular HIV testing would have to be an integral part of any prevention programme using ARVs.
Prevention approaches incorporating ARVs
are still being tested in clinical trials, but are thought to be among the most promising potential interventions against HIV.
One approach, called pre-exposure prophylaxis (PrEP), would involve giving a daily dose of a single ARV drug to people who were HIV-negative but at high risk.
This could be effective in preventing HIV, but not to treat someone already infected. In fact, taking a single ARV drug - instead of the cocktail of three usually prescribed for treating HIV - could result in the virus becoming resistant to that drug or other drugs in the same class. Even more worryingly, people who develop ARV-resistant strains of the virus could infect others with these strains.
A study by Ume Abbas, of the Cleveland Clinic Foundation in Ohio, US, working with colleagues from the University of Pittsburgh, used a mathematical model to determine the probable impact of a PrEP rollout on HIV prevention and drug resistance in a region of sub-Saharan Africa with high rates of HIV.
In an optimistic scenario PrEP reduced HIV infection risk by 75 percent when used by 60 percent of the target population, 5 percent of which were unknowingly already infected. Under such conditions, 2.5 percent of the population would have drug-resistant HIV strains after 10 years.
A pessimistic scenario assumed that PrEP reduced HIV risk by only 25 percent and reached just 15 percent of the population, 25 percent of which were already infected. In this case, 40 percent of the population would experience drug-resistance after 10 years.
A study by McGill University and the McGill AIDS Centre in Montreal, Canada, looked at the potential of ARV-based microbicides
- a lubricant or gel applied prior to sex to prevent HIV transmission - to protect against drug-resistant HIV strains that are likely to become increasingly prevalent in places with large treatment programmes like South Africa.
They found that in laboratory tests, four ARV-based microbicides - now undergoing clinical trials - were all effective against drug-resistant HIV strains, but those using combinations of two ARV drugs were more effective than those using only one drug.
In other laboratory tests they determined that ARV-based microbicides could also contribute to the emergence of drug resistant strains if used by individuals who were already HIV-positive.
The researchers said their findings did not diminish the promise of PrEP and other ARV-based prevention approaches, but offered a clearer view of "what is likely to be needed to ensure that [these approaches] can offer the most benefit to as many people as possible, and with the least amount of risk."