Poor adherence may be an obstacle to intermittent PrEP

Published: June 6, 2012

Adherence to intermittent pre-exposure prophylaxis (PrEP) is significantly poorer than adherence to daily PrEP, according to a study published in PLoS One.

The research involved men who have sex with men (MSM) and female sex workers in Kenya. Average adherence among the individuals taking daily treatment was 83%, but fell to just 55% for those taking intermittent therapy.

However, daily and intermittent PrEP appeared to be equally safe and both regimens were highly acceptable to the study participants.

“Our findings suggest that adherence to intermittent dosing regimens…may be more difficult than adherence to daily dosing,” write the authors.

Nevertheless, they believe that intermittent dosing may still be appropriate “if intracellular drug levels, which correlate with prevention of HIV acquisition, can be attained with less than daily dosing and if barriers to adherence can be addressed”.
PrEP is a promising HIV prevention technology.  It involves HIV-negative people taking daily antiretroviral therapy to reduce their risk of infection with HIV. Its safety and efficacy is currently being investigated in clinical trials. The most widely used regimen is Truvada (FTC/tenofovir).  Results of the iPrEX study involving MSM showed that the therapy reduced the overall risk of acquisition of HIV by 44%. Adherence was key to the success of the treatment. If participants took 90% of more of their doses, then the treatment had 73% efficacy, which increased to 92% among people who had detectable levels of antiretrovirals.

Critics of PrEP cite cost and long-term toxicities as barriers to its use. Intermittent dosing may help overcome these obstacles. But little is known about adherence to intermittent PrEP, its safety and its acceptability to at-risk populations.
Therefore, investigators from the International AIDS Vaccine Initiative (IAVI) designed a prospective, randomised, placebo-controlled trial involving MSM and female sex workers comparing rates of adherence between the two treatment strategies, as well as their safety and acceptability.
The treatment used in the study was Truvada.  Participants were randomised into four arms.

Daily Truvada.

Daily placebo.

Intermittent Truvada (Monday, Friday and within two hours after sex).

Intermittent placebo.

Adherence was recorded electronically each time the cap containing the assigned therapy was opened. Data on post-coital adherence was collected via text messaging.

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