Population pharmacokinetics and pharmacodynamics of imipenem in neutropenic adult patients

Objective: Imipenem is recommended in patients with chemotherapy-induced febrile neutropenia. Although alterations of antibiotic pharmacokinetic parameters have been reported in such patients, little data is available on imipenem.

Methods: Prospective, single-center, non-interventional pharmacokinetic cohort study in adults with chemotherapy-induced febrile neutropenia. Critically ill patients were excluded. Imipenem was administered as a 30-min infusion of 1000 mg/8h. Total imipenem plasma concentrations were assayed by high-performance liquid chromatography during neutropenia and just after neutrophil recovery. We estimated population pharmacokinetic parameters of imipenem by non-linear mixed-effect modelling using the SAEM algorithm.

Results: Sixteen patients were included in the study, including nine women (56.3%), median age 37 years (range, 18.3; 78.3). Eight patients had an hematological malignancy (50.0%) and seven had a solid tumor (43.8%). Imipenem pharmacokinetics were best described by a one-compartment model with first-order elimination. Mean values for imipenem were: clearance 14.3L/h and 10.9L/h and volume of distribution 20.7L and 14.5 L during neutropenia and after recovery, respectively. Imipenem plasma area under the curve at steady state was reduced by 23% during neutropenia. However, all patients achieved a pharmacodynamic target of %fT_>MIC ≥ 40% with a regimen of 1000 mg/8 h or 500 mg/6 h, for MICs up to 2 mg/L. The pharmacodynamics profile for a target of %fT > MIC = 100% was however less favorable with 500 mg/6 h or 1000 mg/8 h either during or after neutropenia.

Conclusion: Pharmacokinetic/pharmacodynamic goals for imipenem were similar in patients during and after neutropenia, despite reduced plasma exposure.