Study Evaluates Doxycycline for STI Prevention Among MSM

Background on STI Incidence

A recent study published in The Lancet examined the effectiveness of doxycycline in reducing the incidence of sexually transmitted infections (STIs) among men who have sex with men (MSM). Despite a decline in new cases of AIDS and other STIs over recent decades, there has been a global rise in STI incidence rates. In the United States, MSM engaging in condomless sex remain the most vulnerable group for STIs, with bacterial infections like gonorrhea, chlamydia, and syphilis becoming increasingly prevalent.

Understanding Post-Exposure Prophylaxis (PEP)

Post-exposure prophylaxis (PEP) refers to the administration of antiretroviral medications following potential exposure to HIV to prevent infection. While pre-exposure prophylaxis (PrEP) has been effective in reducing new HIV/AIDS cases among MSM, bacterial STIs continue to occur at high rates. Currently, there are no effective vaccines for these infections, and condom usage is still the primary prevention method.

Doxycycline, a well-known antibiotic, has previously been utilized for PEP in Lyme disease and leptospirosis. Its potential role in STI prevention is under investigation. The French study published in The Lancet assessed the efficacy of doxycycline PEP in reducing bacterial STI incidence among high-risk MSM.

Study Design and Methodology

The study involved HIV-negative MSM aged 18 and older who were at high risk for HIV acquisition, defined as having engaged in condomless anal sex with at least two different partners in the last six months. Participants were randomly assigned to either an intervention group or a control group.

The intervention group received PrEP with tenofovir disoproxil fumarate and emtricitabine, along with doxycycline PEP. Participants took 200 mg of doxycycline within 24 hours after unprotected sex, with follow-up visits scheduled every two months. Researchers conducted thorough STI testing for syphilis, chlamydia, and gonorrhea at the enrollment visit and during follow-ups over an eight-month period.

Findings on Doxycycline’s Efficacy

Out of 232 participants, 116 received doxycycline PEP while 116 did not. During the follow-up, a total of 78 participants developed a new STI, with 28 in the PEP group and 45 in the control group. The incidence of the first STI was significantly lower in the PEP group. Notably, while the incidence of gonorrhea remained statistically insignificant, there was a significant reduction in chlamydia and syphilis cases among those receiving doxycycline PEP. Overall, the incidence of all STIs was 38 in the PEP group compared to 64 in the control group. Importantly, no HIV seroconversions were reported during the study.

The research indicated that sexual practices remained consistent between the groups, and the frequency of serious adverse events did not show significant differences. This suggests that among MSM using PrEP, doxycycline PEP is associated with a notable decrease in new bacterial STIs. However, the limited follow-up duration may have led to an overestimation of this prophylactic approach’s efficacy.

Concerns and Future Research Directions

The study authors highlighted the need to consider potential antibiotic resistance associated with the PEP approach, particularly concerning antibiotic-resistant strains of gonorrhea. They recommended further studies with longer follow-up periods to better assess the long-term implications of doxycycline PEP before it can be widely endorsed for high-risk individuals.

Conclusion

In conclusion, while doxycycline PEP shows promise in reducing certain bacterial STIs among MSM, additional research is necessary to evaluate its safety and effectiveness comprehensively.

Reference

Molina J-M, Charreau I, Chidiac C, Pialoux G, Cua E, Delaugerre C, Capitant C, Rojas-Castro D, Fonsart J, Bercot B, Bébéar C, Cotte L, Robineau O, Raffi F, Charbonneau P, Aslan A, Chas J, Niedbalski L, Spire B, Sagaon-Teyssier L, Carette D, Le Mestre S, Doré V, Meyer L. Post-exposure prophylaxis with doxycycline to prevent sexually transmitted infections in men who have sex with men: an open-label randomised substudy of the ANRS IPERGAY trial. Lancet. 2018, v. 18, 308-317.