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Updated: Aug 29, 2026

Multiplex Therapeutic Drug Monitoring by Isotope-dilution HPLC-MS/MS of Antibiotics in Critical Illnesses
Published on: August 30, 2018
Imipenem levels are not predictable in the critically ill patient
Howard Belzberg1, Jay Zhu, Edward E Cornwell
1Department of Surgery, Los Angeles County and University of Southern California Medical Center, 90033, USA. belzberg@usc.edu
Background:
Critically ill patients often demonstrate extremely unusual volumes of distribution (Vd) and half-lives (t1/2) of drugs. Imipenem is a widely used antibiotic in critically ill patients.
Methods:
We performed high-performance liquid chromatography analysis of imipenem in samples from 50 critically ill patients treated with either 500 or 1,000 mg.
Results:
Peak imipenem levels varied from 1.56 microg/mL to 58.8 microg/mL. Trough levels varied between 0.0 microg/mL and 15.62 microg/mL. Only 54% of patients maintained a trough level greater than 4 microg/mL. Both the Vd and the t1/2 of imipenem were much greater than observed in other patient populations.
Conclusion:
The pharmacokinetic activity of imipenem in critically ill patients is different from that in other patient populations. There is a very weak correlation between dosage and serum concentrations. Therapeutic failures of imipenem may be because of unpredictable pharmacodynamics (Vd and t1/2) in critically ill surgical patients.
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