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Taking Antibiotics After Unprotected Sex May Reduce STI Risk

New research finds that the antibiotic doxycycline reduces the odds of contracting some bacterial sexually transmitted infections (STIs) if taken within 72 hours of condomless sex.

The findings, presented earlier this year at the Conference on Retroviruses and Opportunistic Infections, came from a study of 232 men who have sex with men (MSM) whose sexual behavior profile put them at high risk for contracting STIs. Half of the men were given a prescription for doxycycline and instructed to take two pills (100 mg) within three days any time they had sex without condoms. The remaining men did not receive the antibiotic regimen; however, everyone was given condoms and counseling about safer sex. All participants were tested for STIs at regular intervals for several months afterward.

Overall, fewer STIs were detected among participants in the doxycycline group. Specifically, 24% of participants who took antibiotics contracted an STI, compared to 39% who contracted one in the control group.

Antibiotic use decreased the risk of contracting syphilis and chlamydia; however, it did not reduce the risk of contracting gonorrhea. Thus, the drug did not appear to be equally effective for all bacterial STIs.

Those in the treatment group used a median of 7 pills per month. Few side effects were reported, and no evidence of risk compensation was observed (meaning that participants who took the drug did not seem to engage in riskier sexual behaviors).

While promising, far more research is needed before we can begin recommending this strategy widely as a means of STI prevention. In particular, we need data that considers groups beyond MSM, examines the long-term effects of this treatment, and considers implications for drug resistance (e.g., would this strategy exacerbate the already growing problem of antibiotic-resistant STIs?). 

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