Interpreting Ceftriaxone Minimum Inhibitory Concentrations Wisely: A Stewardship Approach to Extended-spectrum β-Lactamase and Carbapenem Use

Inappropriate reliance on ceftriaxone minimum inhibitory concentration (MIC) cutoffs as a surrogate for extended-spectrum β-lactamase (ESBL) production remains a major challenge for antimicrobial stewardship. The common practice of treating isolates with MIC ≥2 mg/L as presumptive ESBL producers favors sensitivity but lacks specificity, leading to frequent and unnecessary carbapenem use. A substantial proportion of such isolates instead harbor AmpC or narrow-spectrum beta-lactamases, which do not always require carbapenem therapy. Evidence demonstrates that a ceftriaxone MIC threshold of ≥8 mg/L provides far greater specificity and nearly perfect positive predictive value for ESBL detection. Molecular confirmation of CTX-M, SHV, and TEM genes further improves accuracy and guides rational therapy. Refining MIC interpretation and integrating molecular confirmation into practice are essential to reduce carbapenem misuse, improve stewardship, and preserve antibiotic efficacy.