It's well-documented that taking the antibiotic doxycycline within 72 hours of a risky sexual encounter significantly reduces the risk of sexually transmitted infections (STIs). Recently, the U.S. Centers for Disease Control and Prevention formally recommended this post-exposure strategy.

But what if individuals at high risk for STIs took doxycycline daily, akin to how some use pre-exposure prophylaxis (PrEP) to prevent HIV? Two new studies suggest that this daily regimen, dubbed "DoxyPrEP," could indeed keep STIs at bay.

Both studies will be presented next week at the 25th International AIDS Conference in Munich.

The first study involved 52 gay or bisexual Canadian men living in Toronto and Vancouver. All participants were HIV-positive and had a history of syphilis. For 48 weeks, they were randomly assigned to take either a 100-milligram doxycycline pill daily or a placebo. Of the 52 men, 41 completed the trial.

Dr. Troy Grennan of the British Columbia Centre for Disease Control reported a 79% reduction in new syphilis infections among those taking doxycycline daily. Additionally, gonorrhea infections decreased by 68%, and chlamydia infections dropped by 97%.

The second study focused on another high-risk group: sex workers. Conducted in Tokyo, it tracked 40 female sex workers who were provided with a daily 100 mg dose of doxycycline. The results were significant, with the incidence of any new STI falling from 232 to 79 per 100 person-years. According to Seitaro Abe of Japan's National Center for Global Health and Medicine, syphilis rates dropped to zero among those taking DoxyPrEP, while chlamydia infections declined slightly, and gonorrhea rates remained unchanged.

Beyond physical health, there were potential mental health benefits. Nearly 75% of the women in the Tokyo study reported a significant reduction in their fear of contracting an STI while on DoxyPrEP. Side effects were minimal, with 22.7% experiencing some nausea or vomiting, but no serious adverse effects were reported.

While the findings are promising and support the use of DoxyPrEP in at-risk populations, the researchers stress that larger trials are needed. As these studies are yet to be published in a peer-reviewed journal, the results should be considered preliminary.

These initial results provide hope for an effective daily STI prevention strategy, potentially transforming sexual health practices for high-risk groups.