Doxycycline post-exposure prophylaxis (PEP) taken within 72 hours of unprotected sexual activity may prevent sexually transmitted infections (STIs) in men who have sex with men (MSM), according to a study published in The Lancet Infectious Diseases.

With 1 million STIs acquired daily, STIs are a huge global burden. In addition, increased and growing rates of STIs are reported in MSM despite pre-exposure prophylaxis (PrEP). Therefore, new preventive strategies are needed. Doxycycline PEP has been successfully used in Lyme disease and leptospirosis. This sub-study of the ANRS IPERGAY trial ( identifier: NCT01473472) was an open-label randomized assessment of whether PEP with doxycycline could reduce the incidence of bacterial STIs in high-risk MSM.

A total of 232 HIV-negative men or transgender women having sex with men age 18 or older were included. These participants were considered at high-risk for HIV acquisition defined as having condomless anal sex with at least 2 different partners during the past 6 months. Participants were excluded if they had a symptomatic bacterial STI at enrollment, a doxycycline allergy, or another contraindication for doxycycline use (the use of systemic retinoid or high-dose vitamin A). 

Continue Reading

Participants were randomly assigned to receive PrEP with tenofovir disoproxil fumarate plus emtricitabine and either doxycycline PEP (100 mg; n=116) or no prophylaxis (n=116). For each sexual intercourse event deemed at risk, participants in the doxycycline PEP group were to take 2 doxycycline pills within 24 hours and no longer than 72 hours after sex participants were also instructed not to exceed 6 doxycycline pills per week to reduce the risk for antibiotic selective pressure and adverse events. Study visits were scheduled every 2 months and participants were tested for syphilis, chlamydial, and gonorrheal infections.

Following condomless sexual activity, the use of doxycycline PEP showed a significant decrease in new bacterial STI occurrence. Of the participants, 73 presented with a new STI during follow-up: 28 in PEP, 45 in no PEP (P =.008). Overall, there was a 47% relative reduction in the risk for acquiring a new bacterial STI: gonorrhea, chlamydia, syphilis.

Related Articles

The benefit of doxycycline PEP varied according to STI type. As expected, due to increased antibiotic resistance of gonorrhea, no change was observed in new gonorrheal episode occurrence; 47 participants presented with a new episode of gonorrhea, but there was no significant difference between the PEP and no PEP-groups (P =.52). A significant decrease in the occurrence of new chlamydial infection and syphilis episodes was seen in the doxycycline PEP group; 28 participants presented with a new episode of chlamydia (7 in PEP, 21 in no PEP; P =.006); 13 participants presented with a new episode of syphilis during follow-up (3 in PEP, 10 in no PEP; P =.047). Overall, a 70% relative reduction in the risk for chlamydial infection and a 73% relative reduction in the risk of syphilis were seen; this data is among the highest reported with antibiotic prophylaxis for STIs.

The study investigators concluded that “this strategy might become an effective addition to a combined intervention approach to reduce the high rate of STIs in PrEP users.”


Molina JM, Charreau I, Chidiac C, et al; ANRS IPERGAY Study Group. Post-exposure prophylaxis with doxycycline to prevent sexually transmitted infections in men who have sex with men: an open-label randomised substudy of the ANRS IPERGAY trialLancet Infect Dis. 2018;18:308-317.