Abstract Body

A high incidence of bacterial sexually transmitted infections (STIs) has been reported in several PrEP trials and demonstration projects among MSM. We wished to assess whether on demand post-exposure prophylaxis (PEP) with doxycycline could reduce STIs incidence in this high risk group.

High risk adult MSM being followed in the open-label phase of the ANRS IPERGAY trial with on demand TDF/FTC for HIV prevention, were enrolled in a prospective randomized open-label sub-study. Participants (pts) were randomized 1:1 to take either two pills of doxycycline (100mg per pill) within 72h after condomless sexual intercourse (without exceeding 6 pills per week) or no PEP. All subjects received risk-reduction counseling and condoms, and were tested every 8 weeks for HIV and STIs with serologic assays for HIV and syphilis and PCR assays for Chlamydia trachomatis and Neisseria gonorrhoeae in urine samples, oral and anal swabs. The primary study endpoint was the time to a first bacterial STI: gonorrhoea, chlamydia infection or syphilis. We compared the two study arms according to the intention-to-treat principle. We used time-to-event methods, including Kaplan–Meier survival curves and Cox proportional-hazards models.

From July 2015 to January 2016, 232 pts were randomized, 116 in each arm. Median follow-up was 8.7 months (IQR: 7.8-9.7). Seventy-three pts acquired STIs during the study period, 28 pts in the PEP arm (24%, 37.7 events per 100 pt-years) as compared to 45 pts in the no PEP arm (38.8%, 69.7 events per 100 pt-years) for a hazard ratio (HR) of 0.53 (95% CI: 0.33-0.85, P=0.008). HR for gonorrhoea, chlamydia infection and syphilis were 0.83 (95% CI: 0.47-1.47, p=0.52), 0.30 (95% CI: 0.13-0.70, p=0.006) and 0.27 (95% CI: 0.07-0.98, p<0.05), respectively. Overall 71% of all STIs were asymptomatic. Pts in the PEP arm used a median of 7 pills/month (IQR: 3-13). Safety was good with only 8 pts (7%) discontinuing PEP because of gastro-intestinal adverse events (AEs). Gastrointestinal AEs were reported in 61 pts (53%) and 47 pts (41%) in the PEP and no PEP arms, respectively (p=0.07). There was no significant change in sexual behavior between study arms during follow-up.

On demand PEP with doxycycline reduced the incidence of chlamydia infection and syphilis in high risk MSM and has an acceptable safety profile. The long-term efficacy of this strategy and its impact on antibiotic resistance needs to be assessed.