Sustainability and Impact of an Antimicrobial Stewardship Program on Broad-Spectrum Antibiotic Consumption in South Korea: A 14-Month Extended Follow-Up Study

Background: Antimicrobial stewardship programs (ASPs) are critical for promoting rational antibiotic use. While early implementation outcomes have been reported, extended follow-up sustainability and the impact on high-priority broad-spectrum antibiotics in South Korean secondary/tertiary hospitals require further validation. This study aimed to evaluate the extended outcomes and sustainability of an ASP over a 14-month period. Methods: This retrospective, single-center study analyzed ASP activities from January 2025 to February 2026 at a tertiary hospital in South Korea. Interventions included prospective audit and feedback (PAF) for restricted antibiotics and recommendations for prolonged prescriptions (≥14 days). Primary outcomes were the monthly rejection rate of restricted antibiotics and the acceptance rate of ASP interventions. Secondary outcomes included the days of therapy (DOT) per 1000 patient–days for meropenem and piperacillin/tazobactam (Pip/Taz). Results: During the 14-month period, the ASP intervention acceptance rate increased significantly from a mean of 72.0% in the implementation phase (January–April 2025) to 81.2% in the stabilization phase (May 2025–February 2026) (p = 0.035). The DOT for Pip/Taz decreased significantly from 169.4 to 151.8 per 1000 patient–days (p = 0.002), with a significant negative correlation identified between the intervention acceptance rate and Pip/Taz consumption (r = −0.625, p = 0.017). Although overall meropenem DOT showed seasonal fluctuations without reaching statistical significance across phases, a year-over-year comparison revealed a 7.5% reduction in meropenem DOT (January–February 2025: 54.8 vs. January–February 2026: 50.7 per 1000 patient–days). The rejection rate for restricted antibiotics declined from 3.8% to 2.6%, suggesting that clinicians increasingly self-regulated inappropriate prescribing attempts. Conclusions: The ASP demonstrated extended follow-up sustainability with a significant reduction in the consumption of key broad-spectrum antibiotics. A progressive increase in clinician acceptance of ASP interventions from 72.0% to 81.2%, combined with a concurrent decline in the restricted antibiotic rejection rate, reflected a measurable shift in institutional prescribing culture and confirmed the successful transition to a stabilized program. These findings support the necessity of sustained multidisciplinary ASPs, even in resource-limited settings, to combat antimicrobial resistance effectively.