Adherence to the daily regimen of Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP) against HIV infection varied widely in studies conducted in three different cities. Findings from the study were presented at the Conference on Retroviruses and Opportunistic Infections (CROI) in Boston and reported by aidsmap.

A total of 1,059 gay or bisexual men or transgender women visiting sexual health clinics in San Francisco, Miami and Washington, DC, were offered the chance to be screened for eligibility to participate in an open-label trial of Truvada as PrEP.

Those who sought out the study of their own accord, as opposed to being referred by a doctor, were more likely to be white, have a higher level of education and to be both at high risk of HIV acquisition and to see themselves as at high risk.

The approximately 600 men and trans women who ultimately participated were 32 years old on average. Forty-eight percent of the cohort was white, 35 percent Latino and just 8 percent black.

The study investigators randomly selected about a third of the men to receive drug-level testing to determine their adherence to Truvada. Fifty-two percent of those in San Francisco had levels of the drug in their blood that indicated they were taking the drug daily as prescribed, compared with 35 percent of those in Washington and just 13.5 percent in Miami.

Forty-three percent of the participants in both Miami and Washington and 40 percent of those in San Francisco were apparently taking Truvada about four days a week, which research has suggested reduces the likelihood of HIV transmission by about 96 percent. Thus, 92 percent of the participants in San Francisco, 57 percent of those in Washington and 57 percent of those in Miami were probably protected against HIV acquisition by at least that factor.

The respective percentages of those taking two doses a week, which confers about 70 percent protection, were: 27 percent among Miamians and 4 percent among both Washingtonians and San Franciscans. The respective proportions that took one dose a week, which offers very little protection against HIV, were 11 percent, 2 percent and 4 percent. And finally, a respective 4.5 percent, 2 percent and zero did not have detectable levels of Truvada.

To read the aidsmap story, click here.