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The CDC has moved to recommend doxycycline post-exposure prophylaxis (PEP) for gay and bisexual men and transgender women to prevent sexually transmitted infections (STIs).

With a growing body of evidence showing the antibiotic's effectiveness for the indication, the agency developed the and posted it to , with a 45-day comment period.

Matthew Spinelli, MD, MAS, an infectious diseases physician at the University of California San Francisco, said the proposed guidance was "excellent news on many fronts."

"I am hopeful that the CDC guidance will be helpful in supporting more physicians to discuss doxy-PEP with their patients and to prescribe it," Spinelli told 乌鸦传媒 in an email. "The STI epidemic has been worsening year after year, so it is exciting to have a highly effective biomedical tool to prevent chlamydia, gonorrhea, and syphilis."

The guidelines come at a time when STIs are on the rise in the U.S., and "novel approaches are needed to address the STI epidemic, especially for populations disproportionately affected," the proposed guideline states.

More evidence has accumulated after a small study in 2015 showed pre-exposure prophylaxis (PrEP) with doxycycline reduced the incidence of infection with chlamydia and syphilis. While there have been no additional studies of doxycycline PrEP, CDC reviewed four new studies on doxycycline PEP for reducing STIs.

The open-label extension of the French IPERGAY study, involving men who have sex with men (MSM), showed that patients who received doxycycline PEP had reduced risk of acquiring chlamydia (HR 0.30, 95% CI 0.13-0.70) and syphilis (HR 0.27, 95% CI 0.07-0.98), though there was no difference in gonorrhea infections between the two groups.

In 2022, there were two studies, mainly in MSM, with favorable outcomes for doxycycline PEP. The randomized, open-label DoxyPEP trial in San Francisco and Seattle showed a significant reduction in the incidence of chlamydia, gonorrhea, and syphilis. And the French was stopped early due to efficacy, with doxycycline significantly reducing the risk of gonorrhea (aHR 0.49, 95% CI 0.32-0.76), chlamydia (aHR 0.11, 95% CI 0.04-0.30), and syphilis (aHR 0.21, 95% CI 0.09-0.47), according to the guidance.

An open-label trial of women in Kenya, on the other hand, showed no reduction in STIs, but the CDC reviewers noted there were only two syphilis infections during the study, which also had adherence challenges.

"The limited evidence to support a recommendation in women is unfortunate," Spinelli said. "It is true that in the only study in women it was not effective, but we suspect this was related to lower adherence rather than true biological differences....We are hopeful that additional research will shed light on this topic and support a partial recommendation in women."

At the same time, CDC did raise cautions about the potential for antibiotic resistance with the treatment. Current data suggest "potential risks related to the development of resistance and impacts on the microbiome will need to be closely monitored after implementation of these guidelines," the guidance states.

Doxycycline is a broad-spectrum tetracycline antibiotic. Its most common adverse effects are photosensitivity and gastrointestinal symptoms including esophageal erosion and ulceration, according to the CDC. However, most adverse effects resolve when the medication is stopped.

Some of Spinelli's patients participated in the DoxyPEP trial, and his facility has been an early adopter of the treatment after results were presented at the 2022 International Aids Conference in Montreal.

"The clinics where I work have seen a decline in positive STI tests since doxy-PEP has been widely used," Spinelli said, adding that his patients are "excited to have access to this treatment and appreciative when I prescribe it."

"I think a positive STI diagnosis is an excellent time to discuss your patient's sexual health holistically, including offering HIV PrEP and doxy-PEP for STI prevention," Spinelli added.

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