Pharmacokinetics of phenoperidine in patients undergoing cardiopulmonary bypass

Phenoperidine concentrations were studied, using radioimmunoassay, in five patients submitted to coronary artery bypass graft surgery. Administration of phenoperidine consisted of a 5-mg bolus dose followed by constant infusion of 5 mg h-1. Before cardiopulmonary bypass, phenoperidine concentrations were stable in an individual patient, but there was a large scatter between patients. The concentrations decreased immediately following the start of the bypass, but this decrease was short. During cardiopulmonary bypass, the phenoperidine concentrations increased progressively and were greater at the end of the bypass than before it. The increase in concentration continued following the discontinuation of bypass. The ratios of change of the observed results were in accord with a theoretical evaluation, although the observed concentrations were all greater than those calculated, except at one point. This difference in phenoperidine concentration is probably related to an alteration of liver plasma flow. Haemodilution as a result of the priming of the cardiopulmonary bypass circuit played only a transient role.