Sex frequency and number of doses needed for different pre-exposure prophylaxis regimens among men who have sex with men (MSM) in Bangkok, Thailand

Published: July 18, 2010

Sex frequency and number of doses needed for different pre-exposure prophylaxis regimens among men who have sex with men (MSM) in Bangkok, Thailand

F. van Griensven1,2, W. Thienkrua2, W. Sukwicha2, W. Wimonsate2, S. Chaikummao2, A. Varangrat2, P. Mock1,2

1US Centers for Disease Control and Prevention, APO, Thailand, 2Thailand Ministry of Public Health – U.S. Centers for Disease Control and Prevention Collaboration, Bangkok, Thailand

Background: Time-driven, daily HIV anti-retroviral pre-exposure prophylaxis (PrEP) is being evaluated in safety and efficacy studies in MSM. Based on results from animal studies, event-driven PrEP regimens have been proposed as alternatives, including pre- and post-sexual exposure dosing and bi-weekly standing doses plus post-sexual exposure dose. The number of PrEP doses needed for event-driven dosing however, depends on the sex frequency of MSM. Here we investigate sex frequency and estimate the number of PrEP doses needed for different PrEP regimens among MSM.

Methods: Between February 2008 and May 2009, a cross-sectional sub-study of sex frequency was conducted in a cohort of 823 HIV-negative MSM in Bangkok, using audio-computer-assisted self-interviewing. Based on frequency of reported sex in the past week we calculated the number of doses needed per 100 persons per month (PPM) for event-driven PrEP regimens as follows: ((4 x number of doses per week/823) x 100).

Results: Of 823 MSM (mean age 28.3 yrs, range 19-58 years) 33.3% reported to have had sex on one day in the past week, 15.9% on two days, 7.3% on three days, and 6.9% on four days or more. No sex in the past week was reported by 36.6%. The estimated number of PrEP doses for pre-post-exposure dosing in this cohort would be 1872 per week or 910 per 100 PPM and for bi-weekly standing plus post-exposure dose 2748 per week or 1,336 per 100 PPM. The number of doses needed for daily PrEP would be 5761 per week or 2,800 per 100 PPM.

Conclusions: In this cohort of MSM, pre-post-exposure dosing involved the smallest number of doses of PrEP, followed by bi-weekly standing plus post-exposure dosing, and daily dosing. Actual costs of different PrEP regimens will depend on the antiretroviral agents used and local cost of these drugs.

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