Doxy-PEP use may significantly reduce the risk for STIs

Key takeaways:

• Quarterly chlamydia positivity dropped from 9.6% before doxy-PEP initiation to 2% afterwards among users.
• Syphilis and gonorrhea rates also declined after doxy-PEP initiation.

The rates of chlamydia and syphilis declined dramatically among individuals living with HIV who were prescribed doxycycline postexposure prophylaxis, according to results of a retrospective cohort study.

The findings — published in JAMA Internal Medicine — revealed a modestly reduced rate of gonorrhea among individuals who received doxycycline postexposure prophylaxis (doxy-PEP).

“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,” Michael Traeger, PhD, MSc, a research fellow at Harvard Pilgrim Health Care Institute and the study’s lead author, said in a press release. “We were excited to see that doxy-PEP users in our study experienced declines in chlamydia and syphilis comparable to those observed in clinical trials.”

Traeger and colleagues explained that San Francisco became the first U.S. jurisdiction to issue guidance recommending that doxy-PEP be offered to gay, bisexual and other men who have sex with men and transgender women at risk for STIs in October 2022.

The CDC later published guidance recommending that clinicians discuss the use of doxy-PEP in these patient populations.

In the analysis, the researchers examined the data of 11,515 HIV PrEP users aged 18 years or older who were or were not dispensed doxy-PEP at Kaiser Permanente Northern California from Nov. 1, 2022, to Dec. 31, 2023, to determine how the treatment influenced the risk for STIs.

Among the cohort, 19.5% received doxy-PEP. Men comprised 98.9% of those recipients, and 48.6% had an STI in the year before starting doxy-PEP.

Doxy-PEP users trended older and had used PrEP for HIV longer vs. those not dispensed doxy-PEP.

Traeger and colleagues found that quarterly chlamydia positivity among doxy-PEP users declined from 9.6% (95% CI, 9%-10.3%) before they started the treatment to 2% (95% CI, 1.5%-2.6%) after they started (RR = 0.21; 95% CI, 0.16-0.27), with significant declines observed for all infections sites.

Meanwhile, quarterly syphilis positivity decreased from 1.7% (95% CI, 1.4%-1.9%) before initiation of doxy-PEP to 0.3% (95% CI, 0.2%-0.6%) after initiation (RR = 0.2; 95% CI, 0.11-0.37).

Quarterly gonorrhea positivity dropped from 10.2% (95% CI, 9.6%-10.9%) before doxy-PEP initiation to 9% (95% CI, 8%-10.1%) after initiation (RR = 0.88; 95% CI, 0.77-1), with site-specific declines significant for urethral (RR = 0.56; 95% CI, 0.4-0.79) and rectal (RR = 0.81; 95% CI, 0.67-0.97) gonorrhea.

Incidence of STIs decreased by 1.8% from 2022 to 2023, but the rates of all stages of syphilis and congenital syphilis rose by 1% and 3% during that time, respectively. As such, the findings “highlight the urgent need for innovative tools like doxy-PEP,” Michael Silverberg, PhD, MPH, an HIV epidemiologist at the Kaiser Permanente Division of Research and study co-author, said in the release.

The researchers identified some study limitations. For example, changes in sexual behavior that could have affected STI rates were unable to be assessed, whereas less than 7% of the cohort were Black, meaning the findings may not be representative of all those who may benefit from doxy-PrEP use.

“We know there are important questions that still need to be answered about doxy-PEP, including its effects on antimicrobial resistance,” Julia Marcus, PhD, an associate professor of population medicine at the Harvard Pilgrim Health Care Institute and the study’s senior author, said in the release. “In the meantime, our study suggests that broader implementation of doxyPEP could have tremendous benefits for reducing STI transmission and improving sexual health.”

References:

• New study shows plummeting STIs with doxyPEP use. Available at: https://www.eurekalert.org/news-releases/1069406. Published Jan. 6, 2025. Accessed Jan. 6, 2025.
• Traeger M, et al. JAMA Intern Med. 2024;doi:10.1001/jamainternmed.2024.7186.