Antimicrobial use for the treatment of bacterial sexually transmitted infections among doxycycline post-exposure prophylaxis (DoxyPEP) users in Milan, Italy

Abstract

Background: Doxycycline post-exposure prophylaxis (DoxyPEP) is effective in reducing bacterial sexually transmitted infections (bSTIs) among MSM.

Objectives: The aim of this study is to evaluate whether DoxyPEP introduction is associated with subsequent reduction of antimicrobial use among MSM.

Methods: This is a retrospective study of MSM at the San Raffaele Hospital, Italy, who received DoxyPEP prescription from August 2022 to July 2024. DoxyPEP was suggested for intensive sexual activity (>5 partners). Adjusted %changes in incidence rate of bSTIs before and after DoxyPEP prescription were estimated using a pre-post within-person analysis by Poisson mixed-effects model. Use of DoxyPEP and ceftriaxone, benzylpenicillin and doxycycline for bSTI treatment was quantified as days of therapy (DOTs) per 1000 person-days (1000-PD). The observed DOTs after DoxyPEP prescription were increased with %changes derived from regressions to obtain the expected DOTs in absence of DoxyPEP.

Results: Overall, 754 MSM were prescribed DoxyPEP; during follow-up, 222 (29.4%) reported using DoxyPEP. Median follow-up among DoxyPEP users were 15.8 months (IQR = 12.1-19.2) and 10.8 (6.88-13.1) before and after prescription, respectively. Among DoxyPEP users, 401 bSTIs (Tp 70, Ct 139, Ng 192) were detected before prescription and 146 (Tp 26, Ct 32, Ng 88) after. DOT per 1000-PD was 1.26 for ceftriaxone, 0.37 for penicillin and 3.21 for doxycycline after prescription; DoxyPEP DOT per 1000-PD was 7.00. Expected DOT in the absence of DoxyPEP was 4.85 (95% CI = 3.82-6.41) for ceftriaxone, 1.86 (95% CI = 1.17-2.87) for penicillin and 24.71 (95% CI = 17.18-37.36) for doxycycline.

Conclusions: A significant reduction in antibiotics used for the treatment of bSTIs was achieved among DoxyPEP users.