Biochemical isolation and detection of morphine

High-performance liquid chromatographic determination of morphine and its 3- and 6-glucuronide metabolites by two-step solid-phase extraction

To provide more accurate measurement of morphine and its metabolites for a study of the genetic differences on morphine response, a method for the analysis of morphine and its metabolites is described which has the advantages of increased sensitivity and specificity by using a cleaner extraction. The new extraction method involves both the hydrophobic isolation on a carbon cartridge and ion-exchange isolation on ion-exchange resin which has not preliminary been described for morphine analysis. The combination of these two steps successfully purified drugs from human plasma with maximum removal of interfering substance comparing with a conventional C18 cartridge alone. The analytes are quantified by high-performance liquid chromatography on a reversed-phase C18 column employing a mobile phase consisting of 25% acetonitrile in 0.05 M phosphate buffer (pH 2.1), and 2.5 mM sodium dodecyl sulfate as the pairing ion with a combination of electrochemical and fluorometric detections. The recoveries for morphine (M), morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G) and hydromorphone after the SPE procedure were 86+/-7.1%, 82+/-6.9%, 79+/-6.0% and 85+/-6.0%, respectively. Limits of detection for this method are 0.1 ng/ml for M, and 0.18 ng/ml for M3G and M6G. Limits of quantitation were approximately 0.25 ng/ml for M, and 0.45 ng/ml for M3G and M6G. The present assay was applied to measure M, M3G and M6G content in human plasma to test the applicability and suitability of this method for clinical and research use.

Determination of morphine by high-performance liquid chromatography with electrochemical detection: application to human and rabbit pharmacokinetic studies

A rapid, sensitive, precise and accurate high-performance liquid chromatographic assay with coulometric electrochemical detection was developed for the determination of morphine in human, rabbit, pig and dog plasma. It includes a one-step extraction procedure with hexane-isoamyl alcohol (1:1, v/v) at pH 8.9 (adjusted with phosphoric acid) and reversed-phase liquid chromatography on a microPorasil column. The mobile phase was composed of 5 mM sodium acetate buffer (pH 3.75)-acetonitrile (25:75, v/v). A flow-rate of 1.2 ml/min at 20 degrees C was used. The working potentials for the electrochemical detector were +0.20 V for detector cell 1, +0.55 V for detector cell 2 and +0.75 V for the guard cell. The limit of detection of morphine was 100 pg/ml of plasma. Repeatability, precision and accuracy were also determined concomitantly. The calibration graphs were linear in the concentration range 0.25-250 ng/ml with correlation coefficients of 0.998+/-0.01 and with a minimum intercept of 0.05+/-0.08. The precision in plasma was acceptable, with coefficients of variation less than 11%. The absolute recoveries of morphine and nalbuphine (internal standard) were between 86 and 89% and independent of morphine concentration. Pharmacokinetics after oral morphine [MST Continus (morphine sulphate tablets) 30 mg, Bard Pharmaceutical, Cambridge, UK] in humans revealed a one-compartment first-order absorption model with one absorption phase and one elimination phase. The absorption and elimination half-lives were 2.46 and 1.80 h, respectively. Pharmacokinetics after intravenous morphine (3 mg/kg) in rabbits showed a linear two-compartment open model with one distribution phase and one elimination phase. The distribution and elimination half-lives were 0.5 and 33.8 h, respectively.