Taking 200mg of doxycycline within 72 hours of condomless sex significantly reduces the risk of gonorrhoea, chlamydia and syphilis among men who have sex with men and trans women.
Among those randomized to take doxycycline, 65% fewer were diagnosed with an STI each quarter than those not taking doxycycline.
The DoxyPEP study found that participants in the study were male sex at birth, living with HIV or taking HIV pre-exposure prophylaxis (PrEP) and had a history of an STI and condomless sex with a male partner within in the past year.
They were randomized 2:1 to take open-label doxycycline after condomless sex versus continued standard of care without doxycycline.
Among the 327 participants taking PrEP, there was a 66% reduction in new STIs per quarter (doxycycline 10.7% versus control 31.9%, p<0.001). Of the 174 participants living with HIV, there was a 62% reduction per quarter with doxycycline (11.8% vs 30.5%, p<0.0001).
Participants reported taking doxycycline 87% of the time after condomless sex; 54% reported taking fewer than 10 doses per month, 30% took 10-20 doses per month, and 16% took more than 20 doses per month. No serious or >Grade 2 adverse events were attributed to doxycycline.
Analyses of the impact of intermittent doxycycline on antimicrobial resistance and the gut microbiome are ongoing.
The DoxyPEP study was stopped early in May 2022 when a planned interim analysis showed that those randomized to take doxycycline had substantially fewer STIs.
Co-principal investigator Annie Luetkemeyer, Professor of Medicine at Zuckerberg San Francisco General Hospital at University of California, San Francisco, noted that doxycycline taken after sex is a promising prevention strategy for populations disproportionately impacted by high rates of STIs.
“DoxyPEP represents an important advance in reducing STIs within two vulnerable populations – men who have sex with men and transgender women,” Sharon Lewin, IAS President-Elect and Director of The Peter Doherty Institute for Infection and Immunity, said.
“I look forward to learning more about the implementation of this prevention measure and any long-term effects of using antibiotics for STI prevention.”
The trial was funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, through grant R01AI143439.
It was conducted at the HIV clinic at Zuckerberg San Francisco General Hospital and the San Francisco City Clinic, both part of the San Francisco Department of Public Health, and the Madison Clinic and the Sexual Health Clinic at Harborview Medical Center, both at the University of Washington.