Longitudinal Assessment of Antibiotic Stewardship Programme Implementation and Resistance Trends at a Federal Teaching Hospital in South West Nigeria: A Five-Year Interrupted Time Series Study

Background: Antimicrobial stewardship programmes (ASPs) have been shown to reduce antibiotic consumption and resistance in high-income settings, but longitudinal outcome data from African teaching hospitals remain scarce. Understanding resistance trajectory changes following ASP implementation is essential for evidence-based stewardship investment in Nigeria. This study conducted a five-year interrupted time series analysis of ASP implementation effects on antibiotic use and resistance at a federal teaching hospital in South West Nigeria. Methods: A longitudinal interrupted time series design examined quarterly antibiotic consumption data (defined daily doses per 100 bed-days) and microbiological resistance rates from 2019 to 2024 at a teaching hospital in Ibadan. The ASP was formally implemented in the first quarter of 2021. Segmented regression analysis modelled changes in level and trend of outcomes before and after implementation. Subgroup analyses were performed by antibiotic class and organism. Results: Post-ASP implementation, total antibiotic consumption showed a significant immediate level reduction of 18 percent and a sustained declining trend. Carbapenem use declined most markedly (31% reduction). Resistance rates for Klebsiella pneumoniae showed a delayed but significant declining trend emerging at 18 months post-implementation. Fluoroquinolone resistance rates remained unchanged. Conclusion: ASP implementation at this teaching hospital produced meaningful reductions in antibiotic consumption and partial resistance trend improvements over five years. Class-specific stewardship intensification and sustained investment are required for broader resistance impact. Keywords: antimicrobial stewardship, antibiotic resistance, interrupted time series, teaching hospital, South West Nigeria