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The CDC finalized new guidelines that recommend doxycycline post-exposure prophylaxis (doxy PEP) for at-risk gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) to prevent bacterial sexually transmitted infections (STIs).

Healthcare providers should discuss and offer doxy PEP to people in these populations with a history of at least one bacterial STI -- specifically syphilis, chlamydia, gonorrhea -- in the last 12 months, Lindley Barbee, MD, of the CDC's National Center for HIV, Viral Hepatitis, STD, and TB Prevention, and colleagues wrote in .

"Doxy PEP represents the first new STI prevention tool in decades, at a time when innovation in the nation's fight against STIs is desperately needed," said Barbee in a CDC statement.

The recommendations, rated as AI (strong), are based on the results of four studies. The open-label extension of the randomized French trial, involving MSM and TGW, showed that people who took doxy PEP had about a 70% reduced risk for acquiring chlamydia and syphilis. However, there was no difference in gonorrhea infections between this and the no-medication groups. In 2022, the randomized, open-label , conducted in MSM and TGW in San Francisco and Seattle, and the French , conducted in MSM, showed significant reductions in the incidence of chlamydia, gonorrhea, and syphilis in the doxy PEP arms.

However, one randomized, open-label trial evaluating doxy PEP among Kenyan cisgender women found that it did not prevent STIs, possibly due to poor adherence.

Potential harms of doxycycline administered at the post-exposure prophylaxis dose of 200 mg appear to be generally limited to gastrointestinal side effects, the guideline authors determined.

The guidelines also addressed concerns about the potential for doxy PEP to promote antimicrobial resistance to bacterial STIs and other common bacterial pathogens, but, from current studies, it is difficult to draw conclusions. "Potential risks related to the development of resistance and changes in the microbiome will need to be monitored as these guidelines are implemented," the authors wrote.

The CDC first proposed the recommendations in October of last year.

Guideline Recommendations

According to the guidelines, doxy PEP 200 mg is to be taken once, as soon as possible, within 72 hours of oral, vaginal, or anal sex. The dose should not exceed 200 mg per 24 hours.

Before prescribing doxy PEP, clinicians should counsel at-risk people about its potential benefits and harms. Also, people receiving doxy PEP prescription should be tested at baseline for STIs at anatomic sites of exposure and every 3 to 6 months afterwards. HIV-negative people eligible for doxy PEP should be screened for HIV at baseline and according to current recommendations. Clinicians should reassess the use of doxy PEP every 3 to 6 months.

The doxy PEP prescription should include enough doses to last until the patient's next visit.

Also, prescribing of doxy PEP should be implemented in the context of comprehensive sexual health services, including risk reduction counseling, STI screening and treatment, and linkage to HIV pre-exposure prophylaxis and HIV care.

The guidelines did not include recommendations for use of doxy PEP among MSM and TGW who had not had a bacterial STI in the previous year. However, doxy PEP could be discussed, using a shared decision-making approach with patients in these groups "who have not had a bacterial STI diagnosed during the previous year but will be participating in sexual activities that are known to increase the likelihood of exposure to STIs," they noted.

The guidelines also did not offer recommendations for potentially at-risk cisgender women, cisgender heterosexual men, transgender men, and other queer and nonbinary people. The evidence is insufficient to determine the benefits and harms for these populations, the CDC authors commented.

"Providers should use their clinical judgement and shared decision-making to inform use of doxy PEP with populations that are not part of CDC recommendations," they wrote.

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