Abstract Each year, Clostridium difficile infection (CDI) affects 453,000 Americans, causes 29,000 deaths, and leads to an estimated $4.8 billion in excess costs in acute care hospitals within the US. Effective infection control measures and antibiotic stewardship (AS) are fundamental to sustained control of CDI in healthcare settings. There is an urgent need to identify and implement AS strategies that specifically target CDI by focusing on reducing use of antibiotics highly associated with increased risk of CDI, such as fluoroquinolones (FQ). Preprescription authorization (PPA) and postprescription review with feedback are two core AS strategies. However, it is unclear 1) which AS strategies are most effective in reducing CDI specifically and 2) how to implement AS strategies effectively. Without addressing these critical gaps, CDI prevention will continue to lag. The objective of the proposed study is to evaluate the effectiveness and implementation of a FQ PPA as an AS strategy to target and prevent CDI, promote appropriate antibiotic use, and reduce the transmission of resistant bacteria. This will contribute to the long-term goal of reducing the burden of CDI, which is an essential step in improving the safety and quality of healthcare. FQ PPA is a particularly promising AS strategy to reduce CDI. Although FQs are one of the most frequently utilized classes of antibiotics in inpatient acute care facilities and are closely associated with risk for CDI, FQ usage has not been the focus of control efforts in endemic settings in the US. The proposed study will use an effectiveness-implementation hybrid type 2 design to simultaneously evaluate the efficacy of an FQ PPA intervention to reduce CDI as well as the key considerations for implementing such an intervention successfully. Intensive care units in acute care hospitals throughout Wisconsin will participate in this stepped wedge cluster randomized controlled trial. The specific aims for the proposed study are to: 1) determine the impact of a FQ PPA on hospital-onset and healthcare-associated CDI rates and other clinical outcomes compared with usual care; and 2) evaluate the implementation of FQ PPA using a systems engineering approach. For aim 1, electronic health record data will be used to evaluate the impact of the FQ PPA on hospital-onset and healthcare-associated CDI, as well as other important clinical outcomes. For aim 2, surveys and interviews with healthcare providers will be used to evaluate the contextual, implementation, and work system factors that contribute to successful implementation of a FQ PPA intervention. In addition to addressing an urgent need to identify effective AS strategies, this study will provide a framework to implement and evaluate other interventions for HAI prevention. Regardless of the results, the proposed study will generate data, tools and methods with widespread applicability for AS initiatives in healthcare-associated infection prevention.