A new study indicates that doxycycline post-exposure prophylaxis (doxyPEP) is highly effective in reducing the incidence of chlamydia and syphilis in real-world settings. The research, published in JAMA Internal Medicine, examined the impact of doxyPEP on sexually transmitted infections (STIs) among individuals receiving routine clinical care at Kaiser Permanente Northern California.
The study, led by researchers at the Harvard Pilgrim Health Care Institute, represents the largest cohort of doxyPEP recipients analyzed to date. It found that doxyPEP was associated with a 79% reduction in chlamydia and an 80% reduction in syphilis. A more modest, 12% reduction was observed for gonorrhea.
Study Details and Findings
The research team analyzed pharmacy data from nearly 12,000 HIV pre-exposure prophylaxis (PrEP) users at Kaiser Permanente Northern California, a health system that began offering doxyPEP in November 2022. Of these, 2,253 individuals received doxyPEP within the first year of its availability. The majority of participants were men who have sex with men and transgender women, with a demographic profile similar to the overall PrEP user population.
Researchers compared STI test results before and after the initiation of doxyPEP. The results showed a significant decline in STI incidence: quarterly syphilis rates decreased from 1.7% to 0.3%, and quarterly chlamydia rates decreased from 9.6% to 2%. Gonorrhea rates also saw a decrease, from 10.2% to 9%.
"Since we started offering doxyPEP to our patients, our clinicians have seen a marked decline in both positive STI test results and the number of patients needing treatment after an STI exposure," said Dr. Jonathan Volk, an infectious disease specialist with The Permanente Medical Group and co-author of the study.
Implications and Considerations
The findings suggest that doxyPEP could be a valuable tool in combating the rising rates of STIs, particularly syphilis, including congenital syphilis. "Rising syphilis rates, including more cases of congenital syphilis, highlight the urgent need for innovative tools like doxyPEP," added co-author Michael Silverberg, PhD, MPH, an HIV epidemiologist with the Kaiser Permanente Division of Research.
However, the researchers also noted that the reduction in gonorrhea was less pronounced compared to chlamydia and syphilis. "But the reduction in gonorrhea in our study was modest, underscoring the importance of regular STI testing for patients using doxyPEP," Dr. Volk cautioned.
Concerns about Antimicrobial Resistance
Another important consideration is the potential for increased antimicrobial resistance with widespread doxyPEP use. "We know there are important questions that still need to be answered about doxyPEP, including its effects on antimicrobial resistance," said Julia Marcus, PhD, Harvard Medical School associate professor of population medicine at the Harvard Pilgrim Health Care Institute and senior author of the study.
Despite these concerns, the study authors believe that the benefits of doxyPEP in reducing STI transmission could be substantial. "In the meantime, our study suggests that broader implementation of doxyPEP could have tremendous benefits for reducing STI transmission and improving sexual health," Dr. Marcus concluded.
