Sexually transmitted infections (STIs), particularly bacterial ones, are becoming more prevalent in the United States, with gay men and transgender women being at a higher risk. This increase in STIs has been associated with severe complications such as blindness and congenital syphilis. The emergence of antimicrobial-resistant strains of Neisseria gonorrhoeae (gonorrhea) is a growing public health concern. STIs also increase the risk of acquiring HIV and transmitting it to others.
Effective interventions are needed to stop the rise of syphilis, gonorrhea, Chlamydia trachomatis (chlamydia), and doxycycline postexposure prophylaxis (doxy-PEP) has shown promise in reducing STI incidence, particularly for chlamydia and syphilis. This makes doxycycline a strong candidate for STI prevention.
According to a new study published in The New England Journal of Medicine, taking Doxy-PEP within 72 hours after condomless sex has reduced the incidence of bacterial sexually transmitted infections (STIs) by two-thirds among men who have sex with men (MSM) and transgender women who had previously been diagnosed with a bacterial STI in the past year.
The study showed that Doxy-PEP substantially reduced the incidence of each bacterial STI, including gonorrhea, with consistent reductions in the pre-exposure prophylaxis (PrEP) and people living with HIV (PLWH) cohorts. Moreover, no concerns were identified concerning adverse-event profile, safety, or acceptability.
The results showed that Doxy-PEP was influential among MSM regardless of their HIV status in a socioeconomically and racially diverse population. The study showed an approximately 55% reduction in incident gonorrhea, including pharyngeal gonorrhea. The difference in effectiveness against gonorrhea in this study and the IPERGAY study of Doxy-PEP may be due to the amount of doxycycline taken, adherence, and the prevalence of tetracycline resistance in N. gonorrhoeae isolates.
Although the number of incident syphilis diagnoses was low, there was a reduction in the doxycycline group within the PrEP cohort and a trend toward a reduction in the PLWH cohort. The effect of prophylactic antibiotic strategies on antimicrobial resistance is an important consideration. Among the participants with colonization, a modestly higher proportion had doxycycline resistance in the doxycycline groups than in the standard-care groups.
The study has several limitations, including limited measuring of adherence to doxy-PEP and challenges in accurately ascertaining condomless sex and event-driven PEP use. Moreover, the availability of N. gonorrhoeae culture was limited in some cases. The study was conducted in two West Coast cities, and therefore the acceptability, adherence, and STI rates may vary in other settings.
The low enrollment of transgender women limits generalizability in this population. Additional research and longer follow-up are needed to determine whether doxy-PEP is associated with a substantial selection of resistance in commensal oropharyngeal Neisseria species, the gut microbiome, and other STI pathogens such as Mycoplasma genitalium.