Taking a single dose of the antibiotic doxycycline after sex—known as doxyPEP—has already helped reduce bacterial sexually transmitted infections (STIs) in California, according to three recent real-world studies.

 

In October 2022, San Francisco was the first city to recommend doxyPEP for gay and bisexual men and gender-diverse people. Researchers with the San Francisco Department of Public Health compared monthly STI cases before and after the guidance. Overall, STIs declined significantly citywide after doxyPEP implementation. Chlamydia cases fell by 50%, and early syphilis decreased by 51% relative to predicted levels, though there was a small increase in gonorrhea.

 

In a second study, researchers compared STI rates among people receiving HIV pre-exposure prophylaxis (PrEP) at Kaiser Permanente Northern California—an integrated health system that covers the San Francisco Bay Area and nearby counties—before and after doxyPEP initiation. Recipients saw a 79% reduction in chlamydia and an 80% decrease in syphilis. The 12% decline in gonorrhea was less impressive but still statistically significant. A third study showed reductions in all three STIs in Los Angeles.

 

“Our patients have enthusiastically embraced this proactive approach to reduce their STI risk,” says Jonathan Volk, MD, MPH, of Kaiser Permanente San Francisco. “After doxyPEP became available for our PrEP patients, we have seen a dramatic decline in positive STI tests and less need for treatment after STI exposures.”