In 2010, the Clinical and Laboratory Standards Institute (CLSI) lowered carbapenem breakpoints to reduce the proportion of 'susceptible' organisms that produced carbapenemases. Few studies have evaluated the effect of this change on clinical outcomes. This systematic review aimed to evaluate the effect of carbapenem MICs on 30-day mortality from pooled patient-level data from studies of patients treated with carbapenems across a range of meropenem MICs. PubMed was searched to March 2019 with the terms 'carbapenem', 'meropenem', 'imipenem', 'doripenem', 'ertapenem', 'susceptibility' and 'outcomes'. Studies were included in the analysis if patients had Enterobacteriaceae bacteraemia treated with a carbapenem for ≥48 h and mortality was reported. Studies were excluded if all isolates were either susceptible or resistant to meropenem based on CLSI 2010 breakpoints or if only carbapenemase-producing isolates were included. Authors were contacted for patient-level data. The primary outcome was 30-day mortality, with planned subset analyses of patients treated with meropenem, receiving active combination therapy, treated in the ICU or infected with Klebsiella pneumoniae. Of 157 articles identified, 4 met the inclusion criteria (115 eligible patients). The odds of mortality increased with each increasing meropenem MIC dilution (OR = 1.51, 95% CI 1.06-2.15) as a continuous variable. A similar increase in odds was observed in patients treated with meropenem, treated in the ICU, infected with K. pneumoniae or receiving no other active antimicrobials. Increasing meropenem MICs in Enterobacteriaceae were associated with increased mortality; however, more work is needed to define optimal clinical decision rules for infections within the susceptible range.
Keywords: Bacteraemia; MIC; Meropenem; Susceptibility.
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