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

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