Women need significantly more doses of the antiviral Truvada than their male counterparts in order to prevent HIV infection, according to findings from a new study from the University of North Carolina. It is published in the Journal of Infectious Diseases.

Previous studies showed how Truvada – the only HIV prophylactic approved by the Food and Drug Administration (FDA) – has greater efficacy in men over women, despite similar adherence in both sexes. This new study is the first to explain the mixed results by demonstrating that different tissues require different levels of the drug to fight the virus.

Angela Kashuba, PharmD, senior author and her team created a mathematical model that predicted the drug-to-DNA ratios in vaginal, cervical and rectal tissue. They gave 47 healthy female volunteers Truvada and measured drug levels in vaginal, cervical and rectal tissue, and measured the amount of DNA material present. Using their model, the researchers were able to reach their daily dose calculation needed to prevent HIV infection in women.

Vagina, cervical, and rectal tissue were found to respond differently to Truvada. To prevent HIV infection, twice as much of Truvada was needed in vaginal and cervical tissue vs. rectal tissue because less of the drug made it to those specific tissues. Also, more drug is required because there is more DNA material that the virus uses for reproduction present in vaginal and cervical tissues.

The researchers concluded that women should take Truvada daily to prevent infection. The daily dose regimen of Truvada was approved by the FDA in 2012. In contrary, researchers noted that just 2 doses per week had the equivalent preventative results for men. 

“We would like to remind people who are taking pre-exposure prophylaxis that Truvada should be taken every day to reduce the risk of acquiring HIV infection,” said Kashuba, adding that “Patients should not change their medication regimen without first consulting their physicians.”

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