Truvada has repeatedly been shown to prevent sexual transmission of HIV from infected (mostly) men to their uninfected partners — both men and women — even when protection is not used. Depending on patient compliance, this protection can be as high as 100 percent. But, like most things, one size doesn’t fit all.
Data from a recent study published in the Journal of Infectious Diseases reveal that women who were given the same dose of the drug as men were not protected as well, even when compliance in the two groups was the same.
What is going on here? According to Angela Kashuba, PharmD, senior author of the study and the John and Deborah McNeill Distinguished Professor at the University of North Carolina Eshelman School of Pharmacy, “Our data highlight the fact that one dose does not fit all. ... In determining how best to use drugs to protect people from HIV, we need to understand where in their body they are at risk for being infected, along with the concentration of drug that is needed to protect that site from infection.”
Truvada is a combination medication (Tenofovir plus Emtricitabine) that is in the family of AIDS drugs called nucleoside reverse transcriptase inhibitors (NRTIs) which prevent the virus from producing the genetic material required for replication. In addition to treating HIV+ patients — the original use — the medication can also be taken by those uninfected who are at high risk of becoming so. These groups would include, for example, men who have sex with men, and male-female sex partners where one person (usually the man) is infected and the other is not. (This is referred to as a serodiscordant couple.)
According to the Centers for Disease Control and Prevention, taking Truvada as pre-exposure prophylaxis can reduce rates of sexual HIV transmission by 100 percent when used properly, and by more than 70 percent via drug injection.
Why the difference? The way that Truvada accumulates in tissues is variable. According to the authors, Tenofovir’s metabolite attains a 100-fold higher concentration in colorectal tissue than in the female genital tract (FGT). Additionally, the genetic material in cells of colorectal tissue and FGT have variable response to Truvada, and hence alter the efficacy and subsequent protection conferred by the medicine with respect to the tissue type.
“We are excited to be able to apply our research methods to explain the conundrum of mixed clinical trial results of Truvada prevention, and how men and women should best use HIV prevention therapy,” said Dr. Kashuba. “Yet 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. Patients should not change their medication regimen without first consulting their physicians.”