Senator questions CDC's proposed post-exposure doxycycline recommendation

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US Senator Marc Rubio (R-FL) yesterday sent a letter to Centers for Disease Control and Prevention (CDC) Director Mandy Cohen, MD, MPH, expressing his concerns about the CDC's proposed guidelines recommending the use of doxycycline post-exposure prophylaxis (doxy-PEP) to reduce sexually transmitted infections (STIs).

The draft guidelines, released in October 2023, recommend that men who have sex with men (MSM) and transgender women who have a history of at least one STI in the prior year and are at ongoing risk of an STI take 200 milligrams of doxycycline within 72 hours of condomless sex to reduce the risk of a bacterial STI. The recommendations are based in part on a phase 3 trial conducted in Seattle and San Francisco that found that doxy-PEP reduced chlamydia, syphilis, and gonorrhea in MSM and transgender women by 88%, 87%, and 55%, respectively, without marked changes in the rates of resistance to doxycycline.

Doxy-PEP is one way the CDC is trying to combat skyrocketing rates of STIs, which increased 42% in the United States from 2011 to 2021. Although the guidelines are not yet official, public health departments in San Francisco and other US cities have begun implementing the recommendations.

Concerns about AMR, quality of evidence

In his letter to Cohen, Rubio cited concerns about the potential impact of doxy-PEP on the spread of antimicrobial resistance (AMR), the quality of evidence reviewed by the CDC, and political motivations. Rubio also said he's concerned that the CDC has not clarified whether it will commission additional studies on doxy-PEP's long-term impact on AMR.

"Despite public health officials' longstanding concern about the danger of AMR and overprescribing of antibiotics, the CDC appears now to be throwing caution to the wind," Rubio wrote. "It is important for public health officials to combat STIs with innovative methods, but it is similarly critical that the CDC makes decisions based on science, not demands from activists that downplay the risks of novel treatments.

"The agency must consider the full consequences of its proposals and not mistake short-term successes for long-terms solution without rigorous, high-quality study of available data," he added.

In an email to CIDRAP News in November 2023, Jonathan Mermin, MD, MPH, director of the CDC's National Center for HIV, Viral Hepatitis, STI, and TB Prevention, said the agency is attuned to the potential issue of AMR and had included resistance in its risk-benefit considerations.

"We are also committed to ensuring long-term monitoring, evaluation, and clinical studies are implemented to rapidly identify any issues with antimicrobial resistance and to update our guidelines as needed," Mermin said. "There will be a series of consultations with a diverse group of stakeholders to explore optimal ways to do this."

Rubio asked Cohen to answer questions about the role that AMR experts played in the recommendations, how frequently the CDC will monitor AMR in doxy-PEP users, and whether the CDC will commission long-term studies on doxy-PEP's effect on users' microbiomes.

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