Optimal Spectrum Antibiotic Ratio for assessing antibiotic utilisation in sepsis caused by gram-negative bacilli

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Health Services Research

Background:

• Accurate antimicrobial consumption monitoring is crucial for effective stewardship interventions.
• Hospitals report antibiotic duration using the CDC's Standardized Antimicrobial Administration Ratio (SAAR).
• There is a need for a metric to measure antimicrobial spectrum, complementing SAAR and accounting for local resistance patterns.

Purpose of the Study:

• To develop and evaluate the Optimal Spectrum Antibiotic Ratio (OSAR) as a novel metric for assessing antimicrobial spectrum appropriateness.
• To compare OSAR with existing metrics like SAAR and the Antibiotic Spectrum Index (ASI).
• To identify variations in empirical and directed antibiotic spectrum use and undertreatment across hospitals.

Main Methods:

• Retrospective cohort study of adult sepsis patients with Gram-negative bacilli (GNB) infections across nine hospitals (2018-2023).
• Defined Antibiotic Effective Spectrum (AES) as the ratio of susceptible GNB to all GNB cultured.
• Calculated empirical and directed OSAR as the ratio of clinically chosen AES to the optimal AES, comparing it with SAAR and ASI.

Main Results:

• 10,277 GNB isolates from 7997 patients were analyzed; AES varied from 0.15 (ampicillin) to 0.94 (amikacin).
• Empirical OSAR ranged from 1.08 to 1.89, with 13.6% overall empirical undertreatment and significant hospital variation.
• Directed OSAR ranged from 0.74 to 1.45, and OSAR, SAAR, and ASI showed different trends across hospitals over time.

Conclusions:

• OSAR provides a complementary perspective to duration-based metrics like SAAR for evaluating antibiotic utilization.
• OSAR effectively assesses the appropriateness of antibiotic spectrum based on local and individual resistance data.
• The study highlights significant variations in antibiotic spectrum use and undertreatment, underscoring the need for tailored stewardship interventions.