Doxycycline pre-exposure prophylaxis prevents sexually transmitted infections without affecting vaginal bacterial flora in female sex workers.

11 A separate RCT involving MSM on PrEP documented an 83% reduction in combined chlamydia and syphilis (adjusted HR, aHR = 0.17) per 100 person-years, but its aHR of 0.78 (95% CI 0.60–1.01, P = 0.061) for gonorrhoea did not reach statistical significance. 12 These discrepancies suggest that, while doxyPEP appears highly effective against chlamydia and syphilis, its effectiveness against gonorrhoea may depend on study design, population characteristics and local antimicrobial resistance patterns.

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