A method is described for the measurement of morphine in human plasma by ion-paired reverse-phase liquid chromatography. It includes a novel solid-phase extraction of morphine from plasma which is simple, rapid and complete. No known morphine metabolites could be shown to interfere with the measurements. Determination of morphine pharmacokinetics in patients undergoing heart surgery with 1 mg/kg intravenous morphine produced plasma morphine clearances which agreed with established estimates.
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