Greener Prescribing: A Quasi-Experimental Study of the Environmental Impact of Metronidazole Dosing Interval Optimization

Antibiotics (Basel).

2026 Oct 18;15(10):1035.

PMID: 42938776

PMC13700826

DOI: 10.3390/antibiotics15101035

Abstract

Background: Antimicrobial administration is a major contributor to healthcare-associated waste. We evaluated the environmental impact of changing the default metronidazole dosing frequency from three-times-daily (TID) to twice-daily (BID) administration in a three-hospital system.

Methods: We conducted a quasi-experimental uncontrolled interrupted time-series study across an integrated health system. Inpatient oral and intravenous metronidazole utilization was assessed from January 2023 through December 2024, before and after a change in the default metronidazole dosing on 1 February 2024. Overall utilization was measured as days of therapy (DOT)/1000 days present (DP), and frequency-specific utilization was standardized as dispensed doses/1000 DP. Plastic waste was estimated using EcoRxChoice, and modeled disposal-related carbon dioxide-equivalent (CO2e) emissions reflected facility-specific incineration and transportation processes.

Results: Overall metronidazole utilization remained similar (36.4 pre-intervention vs. 37.2 DOT/1000 DP post-intervention). After implementation TID utilization decreased relative to baseline (-4.41 dispensed doses/1000 DP per month; 95% CI, -6.02 to -2.80 p < 0.001), whereas twice-daily utilization increased (+1.32 dispensed doses/1000 DP per month; 95% CI, 0.37 to 2.27 p = 0.007). Mean modeled plastic waste decreased from approximately 200 to 164 kg/month. Over the 11-month post-intervention period, the monthly trend decreased by 14.63 kg/month relative to the pre-intervention trend (95% CI, -21.42 to -7.83; p < 0.001) and modeled disposal-related 351.3 kg of CO2e.

Conclusions: Optimizing antibiotic dosing frequency is a simple, scalable antimicrobial stewardship strategy that was associated with reductions in modeled metronidazole plastic waste and modeled disposal-related emissions while leveraging the established clinical non-inferiority of twice-daily metronidazole dosing.

antimicrobial stewardship | environmental sustainability | metronidazole | planetary health | plastic waste