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Vaginal microbicides may prevent infection more effectively in men than women
Microbicide resistance was predicted using mathematical models.
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Microbicide gels currently being developed to prevent HIV infection in women could lead to increased HIV drug resistance and more protection in men, according to recent findings.
Sally Blower, PhD, professor of biomathematics at the University of California at Los Angeles, discussed the implications of the model in an interview with Infectious Disease News.
“If this prediction holds true, clinicians will have to closely monitor patients who are using the microbicides,” she said. “If the patients seroconvert, they have to make sure that they discontinue using microbicides to prevent resistance from developing.”
Blower and her colleagues based their models largely on a trial for second-generation microbicides that is currently being conducted in Africa and Europe. They focused on microbicide use in women who had been infected with HIV and whether such use would lead to resistance.
The results were published in the Proceedings of the National Academy of Sciences.
The researchers created two models. In the model for high-risk microbicides, the researchers accounted for a high probability of dapivirine absorption by the vagina. In the low-risk model, they factored in a low probability of absorption.
“We created the two models because we wanted to know the probability of drug resistance emerging if someone is HIV-positive and taking microbicides,” Blower said. “The problem is that people do not yet know whether these microbicides are low-risk or high-risk.” She said that the researchers conducting the trial have been testing frequently and have stopped giving microbicides to participants if they seroconvert. “At the end of the trial, there will be few incidences of resistance, but you will not be able to tell whether it is low-risk or high-risk microbicide.”
From their findings, the researchers predicted that the development of resistance was possible, specifically in realistic situations such as times when use of the microbicides might be inconsistent.
The microbicide prevented infection in up to 21% of women and 27% of men when calculated as a high-risk treatment. When calculated as low-risk, the percentages decreased to 17% for women and 18% for men.
According to the researchers, if a microbicide was not 100% effective and if women did not use it consistently, some of the women would become infected with HIV. Some of the infected women would not be aware of their infection and would continue to use the microbicide rather than additional HIV drugs. The result would be resistance to the microbicide.
Drug-resistant HIV is less likely to be transmitted from one individual to another through sexual contact, according to the researchers. As a result, male sex partners of women who developed the drug-resistant strain may be protected from infection.
“We showed that microbicides, even if they are partially effective, could have a very significant impact on the epidemic by reducing the transmission rate. The message of the paper is very positive about microbicides, but we did want to examine the potential detrimental effects. I think we have done that,” Blower said. – by Rob Volansky
For more information:
- Wilson D, Coplan P, Blower S, et al. The paradoxical effects of using antiretroviral-based microbicides to control HIV epidemics. Proc Natl Acad Sci USA. 2008;105:9835-9840.