Seizures in the critically ill: The role of imipenem

Purpose: To determine the risk of seizures in critically ill patients receiving the antibiotic imipenem, a broad-spectrum antibiotic that has been associated with seizures. Reports generally have not considered other contributing factors such as dose, seizure history, and morbidity index of the underlying illness necessitating the antibiotic. Methods: Charts of all patients in a 450-bed municipal hospital who received imipenem in a 6-month period, as determined by pharmacy records, were reviewed for dosage and duration of imipenem use, occurrence of seizures. and mortality outcome. Attention was paid to demographic features; pattern of seizure occurrence during, before, and after imipenem use; renal function; and correction for dosage based on size. Results: Seventy-five charts were reviewed. Sixty-three patients had no seizures during the hospitalization, four had seizures while receiving imipenem, and eight had seizures during the hospitalization but before or after imipenem use. The incidence of seizures was 4/1,000 patient-days on, and 3.9/1,000 patient-days off imipenem (not significant). The risk of seizure in both groups was considerably higher in those patients with a history of seizures before hospitalization. The presence of other factors that could contribute to increased concentration of imipenem in the brain, such as renal failure or acute stroke, did not contribute to seizure incidence. Metabolic derangement, anoxia, and phenytoin discontinuation did contribute to seizure incidence. Conclusions: Seizure incidence is increased in all critically ill patients (16% of patients studied), but with no added risk during the period patients received imipenem. Determining the proper dose based on a patient's body mass, correction of dose in the presence of renal failure, and avoidance of excess of 2 g/day of imipenem removes any added risk for seizures from imipenem. Despite experimental data to suggest action of imipenem on the glutamate/N-methyl-D-aspartate receptor, or interference with binding to the gamma -aminobutyric acid receptor, and early clinical studies that warned against its use because of seizure risk, we found that careful use of this antibiotic is safe.