BackgroundIDSA published updated practice guidelines for C. difficile infections (CDI) in February 2018. Since publication of previous CDI guidelines in2010, randomized clinical trials (RCTs) have demonstrated benefit of oral (po) vancomycin or fidaxomicin over metronidazole in at least some types of CDI. Updated guidelines endorsed vancomycin or fidaxomicin as recommended treatment for initial and recurrent nonfulminant CDI episodes, and vancomycin as treatment for fulminant CDI. We studied the use of po vancomycin, fidaxomicin and metronidazole in the United States before and after publication of updated guidelines.MethodsWe obtained US antibiotic prescription data (IQVIA, Durham, NC) since 2013, and used standard dosing regimens for treatment of initial CDI to estimate numbers of infections treated with different agents. Po vancomycin and fidaxomicin are used exclusively against known or suspected CDI. Metronidazole is used to treat CDI and other infections. IQVIA data do not capture indications for prescriptions.ResultsTreatment courses of po vancomycin and fidaxomicin increased by 45% (n = 126,729 increase) and 44% (n = 11,243 increase), respectively, over the 12 months after publication of the updated CDI guidelines compared with 12 months before publication (Figure, second arrow; Table). Increased use of both agents was evident in the first month after guidelines were published. Over the same 12 month periods, treatment courses of po metronidazole decreased by 3% (190,430 decrease). In comparison, treatment courses of po vancomycin increased by 24% (n = 47,219 increase) over the 12 months after publication of the multi-national PACT study in August 2014 (Figure, first arrow), which demonstrated superiority of vancomycin over metronidazole. Since 2013, there were no significant increases in the use of fidaxomicin until publication of the updated guidelines.ConclusionUpdated IDSA guidelines have had a major impact on treatment of CDI in the US. RCT data used for guideline updates have been available since 2007–14 and 2011–12 for po vancomycin and fidaxomicin, respectively. IDSA should provide more timely updates to practice guidelines as new data emerge. Annual or bi-annual updates posted in electronic or other nontraditional formats may be more efficient than publishing long-form articles. Disclosures All authors: No reported disclosures.