Now that the U.S. Food and Drug Administration has approved the use of the antiretroviral drug combination of tenofovir disoproxil fumarate and emtricitabine (Truvada®) for HIV prevention, its success will depend on user adherence to the daily drug regimen.
Several trials of Truvada as pre-exposure prophylaxis (PrEP) showed it is most effective when adherence is high. Two trials, VOICE and FEM-PrEP, were unable to determine whether Truvada worked, likely because most participants did not take the study pills daily as directed.
One explanation for low adherence to PrEP is that study participants might have thought they were not at risk of HIV infection.
A study from FHI 360’s Preventive Technologies Agreement (PTA) explored this possibility. Our analysis of data from a randomly assigned cohort of 150 participants who received Truvada in the FEM-PrEP trial yielded some intriguing results, presented in a late-breaker poster this week at the International AIDS Society conference (IAS 2013) in Kuala Lumpur, Malaysia.
Comparing women’s perceived risk of acquiring HIV at the beginning of the trial and their adherence throughout (measured by levels of drug in blood samples), we found no overall association.
But when we looked at what happened over time — comparing what women said about their risk at baseline and weeks 12, 24 and 36 with their corresponding drug levels four weeks later — we found a statistically significant association between perception of risk and adherence.
Our results suggest that participants’ perceptions of HIV risk influenced their adherence. When women felt at risk, it seems, they took the study drug.
It is important to note that these results describe the association between risk perception and adherence among trial participants who were told at each study visit they had been assigned either a study product that might not work or a placebo that would not work. Current PrEP demonstration studies will have the opportunity to assess risk perception and adherence among women who know they are taking a drug that works.