Cost-Effectiveness of Adding Metronidazole to Cefazolin Prophylaxis for Hysterectomy: A One-Year Analysis

INTRODUCTION: Hysterectomy is a clean-contaminated procedure, and surgical site infections (SSIs) remain a common, costly complication. Recent evidence suggests adding anaerobic coverage with metronidazole to cefazolin reduces SSIs. OBJECTIVE: Evaluate the 1-year cost-effectiveness of cefazolin + metronidazole versus cefazolin alone for hysterectomy prophylaxis. METHODS: A decision-analytic model compared cefazolin alone to cefazolin + metronidazole. SSI risks were taken from published cohort data: cefazolin (overall 4.7%; superficial 2.6%, deep 0.58%, organ/space 1.48%) vs cefazolin + metronidazole (overall 2.6%; superficial 1.69%, deep 0.00%, organ/space 0.91%). Costs (USD) applied per SSI type were superficial $9,546, deep $3,345, organ/space $20,458; metronidazole added $2. Health outcomes used EQ-5D utility decrements with piecewise weighting across 12 months: superficial (−0.09, −0.11, −0.06 for <4, 4–9, 9–12 months) and deep/organ-space (−0.10, −0.12, −0.08). Outcomes were expected costs, QALYs, incremental cost, incremental QALYs, ICER, and net monetary benefit (NMB) from a healthcare perspective over 1 year. Uncertainty was assessed with one-way sensitivity (tornado) and probabilistic sensitivity analysis (PSA; 5,000 simulations). Adverse events from metronidazole were explored in sensitivity analyses and had no qualitative impact on conclusions, so were omitted from the base case. RESULTS: Cefazolin + metronidazole reduced expected SSI by 2.1 percentage points versus cefazolin alone. Expected cost/QALY were $2,655 and 0.9973 for cefazolin + metronidazole vs $3,024 and 0.9966 for cefazolin alone, yielding ΔCost −$369 and ΔQALY +0.0007 per patient; combination prophylaxis was dominant. Per 10,000 hysterectomies, this translated to 206 fewer infections and $2.2 million saved. PSA showed cefazolin + metronidazole was cost-effective in 94–95% of simulations across willingness-to-pay thresholds of $50,000–$150,000/QALY. One-way sensitivity identified SSI probabilities and organ/space infection cost as the primary drivers; the preferred strategy did not change across ranges tested. CONCLUSIONS: Adding metronidazole to cefazolin for hysterectomy prophylaxis reduces infections, improves QALYs, and lowers costs at 1 year. Findings are robust to extensive sensitivity analyses, supporting combination prophylaxis as a cost-effective standard of care.Figure 1Figure 2Table 1