On 3/26/19, Infectious Disease fellow Ahmed Babiker presented a review on the paper by Molina et al published in the Lancet of Infectious Diseases in December 2017 titled “Post-exposure prophylaxis with doxycycline to prevent sexually transmitted infections in men who have sex with men (MSM): an open-label randomised substudy of the ANRS IPERGAY trial”  A link to this article can be obtained here.

This was an open -label randomized trial sub-study of the ANRS IPERGAY trial. The ANRS IPERGAY trial was a large RTC conducted in France, which showed the efficacy of on-demand PrEP with tenofovir disoproxil fumarate plus emtricitabine (TDF/FTC) in reducing HIV incidence amongst a high-risk MSM population.2 In this sub-study, the colleagues set out to examine whether post-exposure prophylaxis (PEP) with doxycycline could reduce the incidence of bacterial STIs among high risk MSM.
Patient were randomized to receive either PrEP (TDF/FTC) and doxycycline PEP or PrEP alone. They enrolled 116 men into both groups. Over a median follow up period of 8.7 months, the study participants took a median of 6.8 pills of doxycycline per month and a had a median of 10 high risk sexual intercourse acts (condom-less anal or oral sex) in a 4 week period, with participants having an average of 10 sexual partners in 2 months. No HIV seroconversions occurred during the period. Overall, 73 participants developed a first STI, 28 in the PEP group (incidence, 37.7 per 100 person-years) and 45 in the no-PEP group (incidence, 69.7 per 100 person-years). Doxycycline prophylaxis was effective in reducing the incidence of chlamydia and syphilis in the PEP group, but not gonorrhea. Based on these findings the authors concluded that the use of doxycycline PEP following condom-less sexual activity was associated with a significant decrease in the occurrence of a new bacterial STI.
While the results of this study suggest the on-demand doxycycline PEP may help decrease rates of STIs among high risk groups, a few points to consider are:
The follow up period was short (mean follow up 9 months). The benefit was seen for chlamydia and syphilis but not in gonorrhea. In the US approximately 25% of N. gonorrhoeae are resistant to tetracylines so this intervention would likely also lack efficacy in the US. And in our current climate of rising antibiotic resistance the effect of this strategy on the selection and dissemination of antibiotic resistance for bacterial pathogens implicated in STI and non STI infections remains unknown.
In conclusion this is a provocative study which suggest that there may be a role for antibiotic PEP for the reduction of bacterial STIs among high risk population. HOWEVER, this intervention is not ready yet to be rolled out indiscriminately.  Rather than implementation of the study protocol for all high-risk MSM, the main takeaway might be raised awareness of the burden of STIs in the MSM population and prompt us to do more STI screening.

PUBMED References:

1-Molina JM et al. On-Demand Preexposure Prophylaxis in Men at High Risk for HIV-1 Infection. N Engl J Med. 2015 Dec 3;373(23):2237-46
2- Molina JM et al. 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 Infect Dis. 2018 Mar;18(3):308-317