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Introduction: Both daily and on-demand regimens have been proven effective for pre-exposure prophylaxis (PrEP) against HIV in men who have sex with men (MSM). We aimed to compare the two regimens on their coverage of condomless anal intercourse (CLAI) in MSM. Methods: A randomized, controlled, open-label, crossover trialwas conducted in a teaching hospitalin Hong Kong. Participants were sexually active HIV-negative MSM aged 18 years or above with normalrenalfunction and without chronic hepatitis B infection. Oraltenofovir disoproxilfumarate 300 mg/emtricitabine 200 mg (TDF/FTC) tablets were prescribed for PrEP. After a 2-week lead-in with daily TDF/FTC for treatment-na[up arrow]ve MSM for tolerance assessment, participants were randomly assigned in a 1:1 ratio with a block size of four to either daily-first or on-demand-first arm based on the IPERGAY study, for receiving PrEP for 16 weeks, then crossed-over to the alternative regimen for another 16 weeks. The primary outcome was the proportion of days with PrEP-covered CLAI by intention-to-treat analysis. The trial is registered with the CCRB Clinical Trials Registry, CUHK, CUHKCCRB00606, and is closed to accrual. Results: Between 25 August 2018 and 23 March 2019, 119 eligible participants were assigned to daily-first arm (n = 59) and on-demand-first arm (n = 60) with an 87% overallcompletion rate (n = 103). With 96% and 54% of days on PrEP during daily and on-demand periods, respectively, the proportion of days with PrEP-covered CLAI between two arms were not statistically different (92% vs. 92%, p = 0.93). About half (47%) were diagnosed with at least one episode of incident sexually transmitted infection. Mild and time-limited adverse events, including diarrhoea, headache, nausea and dizziness, were reported in 37 (31%) and 10 (8%) during the daily and on-demand periods, respectively. At the end of the study, a similar proportion favoured daily or on-demand regimen. Conclusions: High prevention-effective adherence, as reflected from the coverage of CLAI, was achievable by either daily or on-demand PrEP among MSM, albeit a higher number of tablets taken for daily PrEP. As both regimens were well accepted, a flexible approach adopting either or both regimens with possible switching is warranted in order to suit individual health needs. Keywords: Asia; clinicaltrials; crossover design; HIV prevention trials; men who have sex with men; PrEP, 1 | INTRODUCTION Pre-exposure prophylaxis (PrEP) with co-formulated tenofovir disoproxil fumarate and emtricitabine (TDF/FTC) is a proven form of biomedical HIV prevention. Following the demonstration of its effectiveness in iPrEx, [...]

Introduction: Daily and event-driven PrEP are both efficacious in reducing the risk for HIV infection. However, the practice of event-driven PrEP (edPrEP) is less well studied, in particular when provided as an alternative to daily PrEP. We studied regimen preferences and switches, and sexually transmitted infection (STI) incidence. Methods: We analysed pooled data from two prospective cohort studies among MSM: Be-PrEP-ared, Belgium and AMPrEP, the Netherlands. In both projects, participants could choose between daily and edPrEP at three-monthly study visits, when they were also screened for sexually transmitted infections including hepatitis C (HCV). We assessed the proportion choosing each regimen, and the determinants of choosing edPrEP at baseline. Additionally, we compared the incidence rates (IRs) of HCV, syphilis and chlamydia or gonorrhoea between regimens using Poisson regression. The study period was from 3 August 2015 until 24 September 2018. Results and discussion: We included 571 MSM, of whom 148 (25.9%) chose edPrEP at baseline. 31.7% of participants switched regimen at least once. After 28 months, 23.5% used edPrEP. Older participants (adjusted odds ratio (aOR) = 1.38 per 10 years, 95% confidence interval (CI) = 1.15 to 1.64) and those unemployed (aOR = 1.68, 95% CI = 1.03 to 1.75) were more likely to initially choose edPrEP. IR of HCV and syphilis did not differ between regimens, but the IR of chlamydia/gonorrhoea was higher among daily users (adjusted incidence rate ratio = 1.61, 95% CI = 1.35 to 1.94). Conclusions: A quarter of participants chose edPrEP at baseline and at 28 months this proportion was similar. Although the IR of HCV and syphilis were similar in the two regimens, the lower incidence of chlamydia and gonorrhoea among edPrEP users may suggest that less frequent STI testing of this group could be considered. Keywords: pre-exposure prophylaxis; sexually transmitted infections; event-driven PrEP; syphilis; men who have sex with men; HIV prevention & control, 1 | INTRODUCTION Oral pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate and emtricitabine, is efficacious for human immunodeficiency virus (HIV) prevention, provided that it is taken correctly [1-3]. Among men [...]