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Zero HIV Infections When PrEP Is Taken 4 or More Times a Week

By Warren Tong

July 24, 2014

Tenofovir/emtricitabine (Truvada) as PrEP (pre-exposure prophylaxis) reduced HIV risk by 100% for all patients who took it at least four times a week, according to results presented by Robert M. Grant, M.D., M.P.H., at the 20th International AIDS Conference (AIDS 2014) in Melbourne, Australia.

The iPrEx Open-Label Extension (OLE) aimed to confirm the effectiveness of PrEP, while identifying demographic and behavioral characteristics associated with PrEP uptake and adherence.

Even though tenofovir/emtricitabine was approved by the U.S. Food and Drug Administration (FDA) for use as PrEP in 2012, uptake has been slow. Between January 2012 and September 2013, only 2,317 patients (half of whom were women) filled prescriptions for tenofovir/emtricitabine as PrEP in the U.S., according to Grant.

The study enrolled 1,603 HIV-negative men and transgender women who have sex with men, all of whom had previously participated in PrEP studies. They were offered 72 weeks of oral tenofovir/emtricitabine as PrEP, with about 76% opting to take the pills and about 23% choosing to participate in the study without taking PrEP at all.


No participant who took PrEP four or more times a week became HIV positive. For those who took the pills two or three times a week, the HIV risk reduction was 84%, showing that adherence doesn't necessarily need to be perfect in order for PrEP to be effective.

However, despite the strong interest in and effectiveness of PrEP, only 5% of participants actually took the pill every day, while only 22% took the pill four to six times a week.

The study measured the use of PrEP by analyzing dried blood spot (DBS) samples, an innovative and sensitive technique for determining long-term PrEP use. Among those taking PrEP, HIV incidence was:

PrEP uptake was 6% higher for those who participated in condomless receptive anal sex (81% versus 75%; P = .003). There was no difference in PrEP uptake by age, education, transgender status, or use of alcohol, methamphetamine or cocaine.

Moreover, looking at drug concentrations in DBS, adherence was higher in those who engaged in condomless receptive anal sex, had multiple sexual partners or had a history of syphilis or herpes.

For the 23% (378 people) who opted not to take any PrEP during the study, the reasons included:

Despite speculation that being on PrEP would lead to "risk compensation," or an increase in riskier sexual behavior, the opposite was observed. Sexual practices among both groups in the study became safer, based on self-report. Syphilis incidence, a marker of sexual risk behavior, was similar between both groups.

The results from this study show a strong interest in PrEP among men and transgender women who have sex with men, particularly those at increased risk for HIV, as well as high levels of effectiveness of PrEP with less than perfect adherence.

[UPDATE 7/31: This article has been updated to add information regarding PrEP adherence rates among iPrEx study participants.]

Warren Tong is the research editor for and

Follow Warren on Twitter: @WarrenAtTheBody.

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