Doxycycline prophylaxis prevents bacterial STIs in Men who have sex with men

New research revealed that there was a two-thirds reduction in the combined incidence of gonorrhea, chlamydia, and syphilis with doxycycline postexposure prophylaxis than with standard care. The study results published in The New England Journal of Medicine validate doxycycline prophylaxis use among men who have sex with men with bacterial sexually transmitted infections. 

Men who have sex with men (MSM) is clinically used to refer to sexual behavior regardless of sexual orientation and comprises a diverse group in terms of behaviors, identities, and health care needs. MSM are at high risk of HIV infection. Preexposure prophylaxis (PrEP) is suggested for MSM in preventing HIV infection. There is a necessity to use interventions for reducing sexually transmitted infections (STIs) among MSM as cisgender men and transgender women are disproportionately affected. Hence researchers conducted an open-label, randomized study to assess the safety and efficacy of doxycycline post-exposure prophylaxis among MSM and transgender women taking HIV preexposure prophylaxis. 

Participants included MSM and transgender women who were taking PrEP against HIV infection (PrEP cohort) or living with HIV infection (PLWH cohort) and who had had Neisseria gonorrhoeae (gonorrhea), Chlamydia trachomatis (chlamydia), or syphilis in the past year. All the participants were randomly assigned in a 2:1 ratio to take 200 mg of doxycycline within 72 hours after condomless sex (doxycycline postexposure prophylaxis) or receive standard care without doxycycline. Quarterly STI testing was done. The incidence of at least one STI per follow-up quarter was the primary endpoint.

Key findings: 

• Among 501 participants, there were 327 in the PrEP cohort and 174 in the PLWH cohort. 
• Of these 67% were White, 7% Black, 11% Asian or Pacific Islander, and 30% Hispanic or Latino.
• In the PrEP cohort, an STI was diagnosed in 61 of 570 quarterly visits (10.7%) in the doxycycline group and 82 of 257 quarterly visits (31.9%) in the standard care group. \
• There was an absolute difference of −21.2 percentage points and a relative risk of 0.34 (95% confidence interval [CI], 0.24 to 0.46; P<0.001).
• In the PLWH cohort, an STI was diagnosed in 36 of 305 quarterly visits (11.8%) in the doxycycline group and 39 of 128 quarterly visits (30.5%) in the standard care group. 
• There was an absolute difference of −18.7 percentage points and a relative risk of 0.38 (95% CI, 0.24 to 0.60; P<0.001).
• The incidences of the three evaluated STIs were lower with doxycycline than with standard care; in the PrEP cohort, the relative risks were 0.45 for gonorrhea, 0.12 for chlamydia, and 0.13 for syphilis, and in the PLWH cohort, the relative risks were 0.43, 0.26, and 0.23, respectively.
• There were 5 grade 3 adverse events and no serious adverse events attributed to doxycycline.
• Of the participants with gonorrhea culture available, tetracycline-resistant gonorrhea occurred in 5 of 13 in the doxycycline groups and 2 of 16 in the standard-care groups. 

Thus, among MSM and transgender women, who recently had bacterial STIs doxycycline PEP reduced the risk of bacterial STIs more than standard care. 

Further reading: Luetkemeyer AF, Donnell D, Dombrowski JC, et al. Postexposure Doxycycline to Prevent Bacterial Sexually Transmitted Infections. N Engl J Med. 2023;388(14):1296-1306. doi: 10.1056/NEJMoa2211934