Doxycycline Postexposure Prophylaxis for Bacterial STIs: Prescribing Patterns, Use, Short-term Outcomes Among 2083 Patients in a Los Angeles Federally Qualified Health Care Program, and Implications for Widespread Use.

Background: Rates of bacterial sexually transmitted infections (STIs) have risen dramatically over the past decades. Doxycycline postexposure prophylaxis (DP) is a novel intervention to prevent bacterial STIs. Recent randomized controlled clinical trials reported high DP efficacy at preventing syphilis and chlamydia in cisgender men who have sex with men and transgender women. Methods: We abstracted data from the electronic health records of 2083 patients at the Los Angeles LGBT Center (the Center) who were prescribed DP between 2019 and June 2024. Patient information included race, income, gender, sex, DP prescriptions, and STI tests dating back to 1998. Results: More than half of the patients prescribed DP at the Center were White, and 48.1% were between 31 and 40 years old. Most of these patients were not diagnosed with an STI in the previous year but ever having an STI correlated with early DP initiation. We demonstrate high real-world DP effectiveness in preventing infections with syphilis (86.4%) and chlamydia (89.7%), and moderate effectiveness for gonorrhea (54.7%), all remarkably similar to published clinical trials. DP use was highly variable, and DP failure for syphilis or chlamydia occurred only in patients with low DP use. There was similar effectiveness for chlamydia and gonorrhea regardless of anatomical site (rectal or throat swabs or urine sample). Conclusions: We show that DP is highly effective at STI prevention in a real-world setting and describe patterns of DP prescribing and use, in addition to STI testing, that can directly inform best clinical practice.