How to prevent sexually transmitted infections in adults

Is pre-emptive treatment the way to go?

- DR. EDSEL MAURICE T. SALVANA

During the recently concluded Philippine Society for Microbiology and Infectious Diseases Annual Convention last Nov. 18 to 20, 2025, I was asked to engage in a friendly debate with colleagues. The issue was whether post-exposure prophylaxis for sexually transmitted infections (STIs) using doxycycline, an antibiotic with activity against several STIs, was appropriate for the Philippine setting. Most Filipinos are familiar with doxycycline as the go-to prophylaxis against leptospirosis after wading in flood waters. Several studies have now shown that it is also effective in decreasing STIS if taken shortly after a high-risk sexual encounter.

Doxycycline is used as an STI treatment primarily against chlamydia infection. Chlamydia is a hard-to-grow bacterium that lives inside human cells and can cause urethritis (inflammation of the urethra, which is the passageway of urine from the bladder to the outside) in both males and females. While it can cause some annoying symptoms in males, chlamydia is particularly dangerous for females since it can cause pelvic inflammatory disease (PID), which is a leading cause of infertility and can progress to sepsis and death. Treatment of chlamydia infection usually entails taking doxycycline 100mg twice a day for seven days. Post-exposure prophylaxis with doxycycline uses a single high dose (two 200 mg tablets) regimen within 72 hours of a high-risk unprotected sexual encounter. Doxycycline post-exposure prophylaxis, or DoxyPEP for short, has been shown in several landmark trials to be effective in decreasing subsequent chlamydia infections in men who have sex with men and transgender women. In addition, it also decreased the rates of gonorrhea and syphilis infection during the trials.