Reference: JAMA Intern Med. 2025 Jan 6 early online
Practice Point: Doxycycline postexposure prophylaxis (doxyPEP) may help reduce STIs in adults using HIV preexposure prophylaxis (PrEP).
EBM Pearl: Measuring pharmacy dispensation of a medication is a surrogate for observed medication use, which introduces a bit more uncertainty into data interpretation.
HIV postexposure prophylaxis has previously been shown to reduce STIs by > 80%. And, there is evidence to support use of postexposure prophylaxis for prevention of other STIs. Doxycycline postexposure prophylaxis (doxyPEP) consists of oral doxycycline 200 mg taken within 72 hours of condomless sex. A retrospective cohort study recently published in JAMA Internal Medicine adds to the growing body of evidence, suggesting that for adults using HIV PrEP who have condomless sex, doxyPEP taken after exposure reduces chlamydia, syphilis, and possibly gonorrhea infection compared to not taking it.
The study included all adults who were dispensed HIV PrEP in the Kaiser Permanente Northern California health system from 2022 to 2023, of which 95% were assigned male sex at birth. During this period, doxyPEP was recommended for persons assigned male sex at birth who had had condomless sex with > 1 partner who had been diagnosed with a bacterial STI within the past year. Gender identity and sexual orientation were not reported, but the cohort was 45% White, 24% Hispanic, 17% Asian, and 6% Black (non-Hispanic). The population was followed for about 6 months after dispensation of doxyPEP.
The study authors analyzed the data in two ways. The first analysis compared STI rates before vs. after starting doxyPEP among participants who had it dispensed by a pharmacy. In this group, quarterly chlamydia prevalence decreased from 9.6% to 2% and syphilis decreased from 1.7% to 0.3%. No differences were found in STIs among the nonusers—those rates remained stable. The second analysis compared doxyPEP users to nonusers and adjusted for potential confounders such as age or type of insurance. These results demonstrated decreased rates of chlamydia (2.1% in users vs. 4.6% in nonusers) and syphilis (0.3% vs. 0.7%) but not for gonorrhea (9.3% vs. 4.7%). However, the reported rates of gonorrhea were composites of tested sites, including urethral, rectal, and oropharyngeal. For gonorrhea, rates of urethral and rectal acquisition were significantly decreased, but not oropharyngeal infections, begging the (unanswered) question whether the lack of overall significance for oropharyngeal infection could be due to participants not considering oral-only sex to be an indication to take doxyPEP.
Ready to write the script? Let’s first outline some limitations. Use of pharmacy dispensing data as a surrogate for actual medication use isn’t ideal and doesn’t mean people actually took the medicine as prescribed. PEP for HIV and STIs is most effective if taken as soon as possible after potential exposure, ideally within 72 hours. Also, the study was retrospective, which limited the ability to control how and what variables were collected, missing data, and biases within the population. Despite all this, for now, having a doxyPEP talk seems like a reasonable idea for those most at risk.
For more information, see the topic Sexually Transmitted Infections (STIs) in Adolescents and Young Adults - Approach to the Patient in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by McKenzie Ferguson, PharmD, BCPS, Senior Clinical Writer at DynaMed. Edited by Alan Ehrlich, MD, FAAFP, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School; Katharine DeGeorge, MD, MS, Senior Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia; Dan Randall, MD, MPH, FACP, Senior Deputy Editor at DynaMed; Rich Lamkin, MPH, MPAS, PA-C, Clinical Writer at DynaMed; Matthew Lavoie, BA, Senior Medical Copyeditor at DynaMed; Hannah Ekeh, MA, Senior Associate Editor II at DynaMed; and Jennifer Wallace, BA, Senior Associate Editor at DynaMed.