A Strategy for Reducing STIs Through Implementing Doxycycline Post-Exposure Prophylaxis


Study presented at CROI 2024 reveals that the introduction of Doxycycline post-exposure prophylaxis (doxy-PEP) guidelines in San Francisco has significantly decreased the incidence of chlamydia and syphilis

STI test| Image Credits: Unsplash

The Department of Public Health in San Francisco (SF) distributed guidelines through community and public health channels, underscoring the use of doxy-PEP as a strategy for reducing bacterial STIs among men who have sex with men (MSM) and transgender women (TGW).1

The introduction of SF doxy-PEP guidelines and their early adoption in high-volume clinics correlated with ongoing reduction in reported cases of chlamydia (CT) and early syphilis (ES), but not gonorrhea (GC), among MSM/TGW across a span of 13 months. Additional elements, such as variations in screening habits and sexual behaviors may have influenced the trends.

Between November 1, 2022, and September 30, 2023, a total of 3,288 MSM and TGW began doxy-PEP treatment at 3 sentinel clinics. Post-implementation of doxy-PEP guidelines, there was a citywide decline in the monthly reported cases of CT by 6.7% per month (p<0.0001) and ES by 3.12% per month (p<0.0001) among MSM/TGW, compared to projections from models. After 13 months into the post-guideline period, there was a 51% reduction (95% CI: 39%-60%) in CT cases and a 50% reduction (95% CI: 38%-59%) in ES cases, relative to the anticipated figures for November 2023. However, there was no significant alteration observed in GC cases (p=0.087). In contrast, the number of monthly reported CT cases among cisgender women rose by 2.43% per month (p<0.01) during the post-guideline period.

Researchers monitored the quarterly number of new patients initiating doxy-PEP from 3 high-volume SF sexual health clinics. To assess the ecological association between doxy-PEP program implementation and citywide STI incidence, interrupted time series analyses on monthly reported SF cases of CT, GC, and ES, among MSM/TGW before July 1, 2021, through October 31, 2022, and after November 1, 2022, through November 30, 2023, release of doxy-PEP guidance. Using an autoregressive integrated moving average model to see expected post-period monthly case counts in the absence of doxy-PEP. Observed case counts were based on citywide surveillance data. Analyses were repeated for monthly CT case counts among cis women for comparison.

This research on the challenges and opportunities of doxy-PEP is being presented at the ongoing Conference on Retroviruses and Opportunistic Infections (CROI) in Denver, CO. Future studies are planned, using data from an extended period after the guideline introduction, to determine whether these trends continue in line with the citywide uptake of doxy-PEP and to assess for any disparities in the use of doxy-PEP and STI incidence among different demographic groups.

Recent Doxy-PEP Studies

The effectiveness of HIV post-exposure prophylaxis (PrEP and PEP, respectively) may inadvertently encourage condomless sexual intercourse, potentially leading to the transmission of bacterial STIs. Pursuing the success of HIV PrEP and PEP, research on doxy-PEP, the drug active against major bacterial STIs, has been progressing. A recently accepted manuscript in Clinical Infectious Diseases highlights the US DOXY-PEP study, which showed that doxycycline, administered at a dose of 200mg orally by cisgender men and transgender women within 72 hours of condomless sexual intercourse, significantly reduced bacterial STIs compared to a placebo.2

The study revealed relative risk reductions of 73% and 66%, indicating a strong protective effect against CT and ES. Despite variations in effectiveness against different pathogens, the results affirm doxy-PEP's potential as an effective public health measure to lower bacterial STI incidence among high-risk populations.

Reflecting on CROI's poster on the challenges and opportunities, the current data endorse doxy-PEP's application in preventing bacterial STIs in cisgender MSM and TGW. However, concerns regarding safety and antimicrobial resistance necessitate further investigation.


  1. Sankaran M, Glidden D, Kohn R, et al. Doxy-PEP Associated With Declines in Chlamydia and Syphilis in MSM and Trans Women in San Francisco. Poster #127 presented at CROI 2024. March 3-6, 2023. Denver, CO.
  2. LaRosa S. Doxy-PEP to Prevent Bacterial STIs: Proceed But With Caution. Contagion. Published February 20, 2024. Accessed March 4, 2024. https://www.contagionlive.com/view/doxy-pep-to-prevent-bacterial-stis-proceed-but-with-caution
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