Pharmacokinetics of cimetidine in critically ill patients.

Cimetidine disposition was studied after rapid (1 min) intravenous infusion in eight critically ill patients aged between 20 years and 77 years; one patient was studied on two occasions. Cimetidine dose was 300 mg in seven patients and 400 mg in the remaining patient. Arterial plasma cimetidine concentrations at the end of the infusion were very high and ranged from approximately 15-35 mg/l. Pharmacokinetic parameters displayed wide interpatient variability (coefficients of variation of 30-50%) and significant relationships emerged between some of these parameters and certain patient characteristics. Most notable, total systemic plasma clearance of cimetidine was directly related to estimated creatinine clearance (p less than 0.01). This relationship might prove to be a useful method of individualizing cimetidine dosage in critically ill patients.