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  Conference on Retroviruses
and Opportunistic Infections (CROI)
February 13-16, 2017, Seattle WA
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PEP With Doxycycline Halves Bacterial STI Rate in MSM on TDF/FTC PrEP
  Conference on Retroviruses and Opportunistic Infections (CROI), February 13-16, 2017, Seattle
Mark Mascolini
Postexposure prophylaxis (PEP) with doxycycline almost halved the incidence of bacterial sexually transmitted infections (STIs) in men who have sex with men (MSM) taking as-needed tenofovir/emtricitabine (TDF/FTC) preexposure prophylaxis (PrEP) in an extension of the French IPERGAY trial [1]. The IPERGAY team cautions that antibiotic prophylaxis for STIs cannot be recommended until more research confirms its value.
IPERGAY found that TDF/FTC PrEP before and after sex cut the new-HIV rate 86% compared with placebo [2]. But antiretroviral PrEP does nothing to ward off non-HIV STIs, which affected 41% of the sexually active men in IPERGAY. Doxycycline PEP has been used to prevent Lyme disease, leptospirosis, and scrub typhus, but antibiotic prophylaxis for STIs has met with limited success. One recent 30-man randomized trial found lower syphilis incidence among men using daily doxycycline PEP than in men not using PEP [3]. The IPERGAY team figured that an HIV PrEP trial offered a unique opportunity to test PEP for STIs.
The doxycycline analysis involved HIV-negative MSM enrolled in the IPERGY open-label extension study. Researchers randomized them to as-needed doxycycline PEP (200 mg 24 to 72 hours after sex) or to no PEP. Men made study visits at baseline and every 2 months to get tested for syphilis, chlamydia, and gonorrhea in urine samples, anal swabs, and throat swabs. The investigators figured that a study of 276 men would have 80% power to detect a 55% relative decrease in STI incidence with PEP. They actually randomized 232 men equally to PEP or no PEP, of whom 106 in each group (91%) completed follow-up.
The PEP and no-PEP groups had median ages of 38 and 39, 95% in both groups were white, and 42% in both groups used psychoactive drugs. Both groups reported medians of 10 sex acts in the past 4 weeks and 10 sex partners in the past 2 months. Proportions with an STI history were 19% in the PEP group and 14% in the no-PEP group.
Through a median follow-up of 8.7 months, 73 men picked up a new STI, including 28 in the PEP group (37.7 per 100 person-years) and 45 in the no-PEP group (69.7 per 100 person-years) (P = 0.007). Those rates worked out to a hazard ratio (HR) of 0.53 (95% confidence interval [CI] 0.33 to 0.85, P = 0.008), meaning men using doxycycline PEP had a 47% lower risk of getting an STI. PEP did not protect men from gonorrhea (HR 0.83, 95% CI 0.47 to 1.47, P = 0.52). But it lowered the gonorrhea risk by 70% (HR 0.30, 95% CI 0.13 to 0.70, P = 0.006) and cut the syphilis risk by 73% (HR 0.27, 95% CI 0.07 to 0.98, P < 0.05).
Most men in the PEP arm, 83%, used PEP within 24 hours of sex, taking a median of 6.8 pills per month. Three men in the PEP group (2.5%) never started PEP and 29 (25%) stopped PEP during the study. Gastrointestinal problems were the main reason for stopping PEP, leading to 8 discontinuations (7%). Twenty-eight men in the PEP group (24%) and 16 in the no-PEP group (14%) had drug-related gastrointestinal problems during the study (P = 0.05). Lab abnormality rates did not differ significantly between the two study arms. Median numbers of sex acts or sex partners and rates of condomless receptive anal intercourse did not change during the study and did not differ between the PEP arm and the no-PEP arm.
The researchers conclude that doxycycline PEP almost halved the rate of bacterial STIs in these MSM. They believe the intervention had acceptable safety, with only 7% of participants stopping the antibiotic because of side effects. Principal investigator Jean-Michel Molina stressed the need for caution in interpreting these findings, which "have to be confirmed in another study with longer follow-up before we can make any recommendation."
1. Molina JM, Charreau I, Chidiac C, et al. On demand post exposure prophylaxis with doxycycline for MSM enrolled in a PrEP trial. Conference on Retroviruses and Opportunistic Infections (CROI), February 13-16, 2017, Seattle. Abstract 91LB.
2. Molina JM, Capitant C, Spire B, et al; ANRS IPERGAY Study Group. On-demand preexposure prophylaxis in men at high risk for HIV-1 infection. N Engl J Med. 2015;373:2237-2246. http://www.nejm.org/doi/full/10.1056/NEJMoa1506273
3. Bolan RK, Beymer MR, Weiss RE, Flynn RP, Leibowitz AA, Klausner JD. Doxycycline prophylaxis to reduce incident syphilis among HIV-infected men who have sex with men who continue to engage in high-risk sex: a randomized, controlled pilot study. Sex Transm Dis. 2015;42:98-103. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295649/