A Known Antibiotic Could Be a Fierce Weapon in STI Fight

The inexpensive antibiotic doxycycline has been around for years—but new research indicates it may be more versatile than previously known. NPR reports that when taken within 72 hours of condomless sex, studies have shown that doxy-PEP (that's short for post-exposure prophylaxis) may protect against contracting sexually transmitted infections. Specifically, three biggies: chlamydia, gonorrhea, and syphilis. An April study found that gay and bisexual men and transgender women who were already taking HIV PrEP saw a 65% drop in new STIs. Figures like that one are so promising the CDC intends to introduce guidelines to aid health practitioners with prescribing it later in the summer; the San Francisco Department of Public Health did the same months ago, CBS News reported.

But there is a big asterisk to the news: The most promising research has, as in the aforementioned study, involved gay and bisexual men and transgender women, and researchers believe men in general could benefit. But a study involving 400 at-risk Kenyan women showed no benefit, with study leader Dr. Jenell Stewart suggesting the study results could be due to "differences in anatomy, differences in antimicrobial resistant strains in different parts of the world, and adherence" to the medication. She called the findings "a huge disappointment," though she cautions that more study is needed. And there's another entry on the caution front: NPR notes "the implications for antibiotic resistance need to be closely monitored."

Indeed, a press release on the April study noted "the research also revealed a slight increase in antibacterial resistance that requires further exploration." Still, "effective methods for preventing sexually transmitted infections are badly needed," said National Institute of Allergy and Infectious Diseases director Hugh Auchincloss at the time. CDC estimates put the number of cases of syphilis, gonorrhea, and chlamydia at 2.5 million in 2021, up from 2.4 million in 2020, with that increase having "a disproportionate impact among MSM [men who have sex with men] and transgender women." (More STDs stories.)