A new antibiotic prevention strategy has led to dramatic reductions in some sexually transmitted infections, with rates of chlamydia and syphilis dropping by about 80% among recipients, according to a large-scale study published in JAMA Internal Medicine.
The research, which followed more than 11,500 patients at Kaiser Permanente Northern California, examined the effectiveness of doxycycline post-exposure prophylaxis (doxyPEP) when implemented in routine medical care. The strategy involves taking the antibiotic within 72 hours after sex.
“Interventions that are effective in clinical trials don’t always end up working in real-world settings, where people tend to face more barriers to consistent medication use,” says Michael Traeger, lead author and research fellow at Harvard Pilgrim Health Care Institute.
The study found that about one in five patients using HIV prevention medication opted to receive doxyPEP during its first year of availability. Among these recipients, quarterly rates of chlamydia fell from 9.6% to 2.0%, while syphilis rates decreased from 1.7% to 0.3%. Effects on gonorrhea were more modest, with rates declining from 10.2% to 9.0%.
“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,” explains Jonathan Volk, an infectious disease specialist with The Permanente Medical Group.
The findings come as U.S. health officials report more than 2.4 million cases of these infections in 2023, including nearly 4,000 cases of congenital syphilis, which resulted in 279 stillbirths and infant deaths.
While the results show promise, researchers noted some limitations. The antibiotic appeared less effective against throat infections, and monitoring for potential antibiotic resistance will be crucial as the strategy becomes more widely used.
“Rising syphilis rates, including more cases of congenital syphilis, highlight the urgent need for innovative tools like doxyPEP,” adds Michael Silverberg, an HIV epidemiologist with Kaiser Permanente.
The strategy is now recommended by the Centers for Disease Control and Prevention for gay and bisexual men and transgender women who have had a bacterial STI in the past year. However, researchers note that ensuring equitable access to this prevention option remains a challenge, as the study found higher uptake among those with commercial insurance.
“We know there are important questions that still need to be answered about doxyPEP, including its effects on antimicrobial resistance,” says Julia Marcus, senior author and Harvard Medical School associate professor. “In the meantime, our study suggests that broader implementation of doxyPEP could have tremendous benefits for reducing STI transmission and improving sexual health.”