A pharmacokinetic approach to postoperative pain: continuous infusion of pethidine.

In an attempt to improve postoperative pain management an intravenous infusion of pethidine was designed to provide stable therapeutic blood concentrations. Ten female patients undergoing elective abdominal hysterectomy were studied. After commencement of the infusion, blood pethidine concentrations increased rapidly and exceeded 0.46 microgram/ml after four hours. The mean steady-state concentration of 0.67 microgram/ml was reached by twenty-four hours. This infusion regimen resulted in the abolition of severe pain after three hours and analgesia continued for the duration of the two day study. Significant blood concentrations of the metabolite norpethidine were found although clinically no toxic effects were observed. Side effects of pethidine were infrequent. Controlled continuous intravenous infusion of pethidine produced stable blood concentrations and provided excellent pain control.