Antimicrobial stewardship strategies for implementing the 2019 EUCAST "I" definition

BACKGROUND: In 2019, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) redefined the “I” category from “intermediate susceptibility” to “susceptible, provided increased exposure”. This shift emphasizes higher antibiotic dosing, alongside removal of the “S” category for some species. Our hospital implemented standard measures and an active monitoring program to support this change. This study evaluates the impact of this multifaceted strategy. METHODS: A revised dosing table, selective reporting, structured electronic medication orders and hospital-wide communication were introduced. In February 2022, an active monitoring program with 13 clinical rules was implemented in our pharmacy-based Check of Medication Appropriateness service, continuously screening patients’ records for inappropriate antimicrobial prescriptions, with pharmacists sending recommendations to physicians. Pharmacy and microbiology departments collaborated to implement this strategy. The number of recommendations and acceptance rates were measured over 30 months (February 2022-July 2024). A retrospective evaluation assessed spontaneous uptake of standard implementation measures for Pseudomonas infections (February 2022-January 2023). An interrupted time series analysis compared pre- and post-implementation periods to measure impact on broad-spectrum hospital-wide antibiotic consumption, infectious diseases (ID) specialist consultations and hospital acquired Clostridioides difficile associated diseases (CDAD). RESULTS: Spontaneous uptake of 2019 EUCAST “I” guidelines for Pseudomonas infections, based on standard implementation measures, was 78%. Over 30 months, 1688 recommendations were given, with an 87% acceptance rate. Broad-spectrum antimicrobial consumption, especially consumption of meropenem, remained stable or even decreased post-intervention. ID consultations significantly increased post-intervention (p = 0.0023). Hospital acquired CDAD remained stable. CONCLUSION: Our multifaceted strategy, including active monitoring, effectively supported the 2019 EUCAST “I” implementation. Selective reporting is important for spontaneous uptake, while clinical rules guided correct antibiotic dosing. Pharmacist- and microbiologists-driven recommendations were well-accepted, reducing inappropriate prescriptions while well controlling consumptions of broad-spectrum antimicrobials and hospital acquired CDAD.