517. Impact of Doxycycline in Place of Azithromycin for Community-Acquired Pneumonia on Clostridium difficile Infections

Background As antimicrobial exposure represents a major risk factor in the development of Clostridium difficile infection (CDI), optimization of antimicrobial selection is critical. While a number of antibiotics have been associated with increased risk of CDI, doxycycline may be considered protective. The combination of ceftriaxone and doxycycline (CTX-D) is supported by the Infectious Diseases Society of America (IDSA) for the management of community acquired pneumonia (CAP). The primary objective of this study was to evaluate if CTX-D is associated with a reduced incidence of CDI compared with ceftriaxone and azithromycin (CTX-A) among nonintensive care unit (ICU) patients with CAP at Christiana Care Health System. Methods A retrospective cohort study was conducted to evaluate patients who received CTX-D or CTX-A admitted to Christiana Care between June 1, 2015 and December 31, 2017. Non-ICU patients, aged 18 years or older, receiving at least one dose of CTX-D or CTX-A were included. The primary outcome of our study was the incidence of CDI within 30 days from initial dose of CTX-D or CTX-A. The secondary outcome was the time to onset of CDI from initial dose of CTX-D or CTX-A. Results One thousand sixty-four unique patients were included in this study. Overall, 778 patients received CTX-D and 286 received CTX-A. Among patients who received CTX-D, 2 patients developed CDI, compared with five patients who received CTX-A (relative risk, 0.15; 95% confidence interval, 0.03–0.75; P = 0.02). The mean time to onset of CDI from initiation of CTX-D was 22 days compared with 9.2 days from initiation of CTX-A. Conclusion In this cohort of non-ICU patients with CAP, CTX-D was associated with a reduced incidence of CDI. Further studies are necessary to confirm these preliminary findings to optimize clinical practice, while minimizing potential adverse outcomes associated with antimicrobial use. Disclosures All authors: No reported disclosures.