Predicting doripenem susceptibility based on meropenem and imipenem interpretation for Pseudomonas aeruginosa

Doripenem is not available on many automated susceptibility testing panels. We evaluated the surrogate predictive value (SPV) of meropenem and imipenem in predicting doripenem susceptibility using the different breakpoint definitions available globally. MIC data for 736 Pseudomonas aeruginosa were extracted, and categorical interpretations were performed using Clinical and Laboratory Standards Institute (CLSI) proposed 2012, European Committee on Antimicrobial Susceptibility Testing (EUCAST), and Food and Drug Administration (FDA) breakpoints. Regardless of the breakpoint applied, very major and major errors were observed in only 0.1-0.8% and 0.1-4.5% of isolates, respectively. Meropenem's SPV was 98.6% for CLSI 2012 breakpoints, 94.0% for EUCAST, and 95.0% for FDA. Imipenem's SPV was 98.6%, 90.9%, and 97.2%, respectively. These data indicate that meropenem and imipenem would be reliable surrogate markers of doripenem susceptibility when using CLSI 2012 and FDA breakpoints. Meropenem would be recommended over imipenem for EUCAST breakpoints. However, meropenem and imipenem nonsusceptible isolates should be directly tested against doripenem since the latter antibiotic may still retain susceptibility against these isolates.