According to a mathematical model, vaginal and rectal microbicide gels used to prevent HIV infection in women may lead to drug-resistant strains of the virus, Australia’s ABC Science Online reports ( Researchers also found that microbicides may actually protect heterosexual men from infection more than their female peers.

The study—published in the July 8 issue of the Proceedings of the National Academy of Sciences—examined microbicide gels in development and built a virtual model to see if microbicides could potentially increase HIV drug resistance. ABC Science Online reports that if women do not use a microbicide gel consistently and if the gel was not proven to be 100 percent effective, then a small percentage of those women might unknowingly become infected with HIV. If those women continue to use the gel without taking additional antiretroviral medications, the viral strain may become more resistant to drugs.

Researchers said they were surprised to learn that although microbicides were initially developed as a female alternative to condoms, heterosexual men may reap more of the preventative benefits of HIV microbicides. According to the study’s mathematical model, microbicides theoretically are more likely to prevent female-to-male transmission of the virus.

“Paradoxically, although microbicides will be used by women to protect themselves against infection, they could provide greater benefit to men,” the researchers say.