People tend to follow the standard daily-dosing regimen for PrEP better than intermittent dosing schedules, according to a study of 536 people in Bangkok, Thailand; Harlem in New York City; and Cape Town, South Africa.

All participants were randomized to receive PrEP with instructions to take Truvada according to one of three protocols: daily; twice a week plus an extra dose following sex; or purely intercourse-based dosing, with one dose up to 48 hours before anticipated sex and another two hours after sex.

The Bangkok and Harlem groups enrolled men who have sex with men (MSM) and a few transgender women while the Cape Town trial enrolled women.

Considering participants’ adherence rates and sexual activity, the daily, twice-weekly and intercourse-based dosing protected an estimated 85, 79 and 65 percent of sexual acts, respectively, in Bangkok. The corresponding respective rates in Harlem were 65, 46 and 41 percent; and in Cape Town they were 76, 65 and 53 percent.

Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, says the study “shows that diverse groups of men and women can adhere to daily dosing, which is the only dosing regimen that is currently proven effective at reducing the risk of HIV infection. Further research is needed to determine the efficacy of alternative dosing regimens in preventing HIV, as studies to date do not conclusively support intermittent use of PrEP.”