High-performance liquid chromatographic determination of naltrexone in plasma of hemodialysis patients

A simple, sensitive, selective and reliable reversed-phase high-performance liquid chromatographic (HPLC) method with UV detection is described for th e determination of naltrexone in plasma samples. Naltrexone and the interna l standard, naloxone, were isolated from plasma either with a liquid-liquid extraction method using ethyl acetate or with a solid-phase extraction met hod using Sep-Pack C-18 cartridge before chromatography. The extracts were dried under a stream of nitrogen and the samples were reconstituted in the mobile phase, then 20 mu L were injected on a Waters Symmetry C-18 column ( 5 mu m particle size, 4.6 x 150 mm). The mobile phase consisted of 0.06% tr iethylamine (pH 2.8)-acetonitrile (92:8, v/v) pumped at 1 mL/min. The peak- area ratio versus plasma concentration was linear over the range of 10-500 ng/mL and the detection limit was less than 8 ng/mL. Quantification was by ultra-violet detection at 204 nm. The present method was applied to the det ermination of the plasma concentration of naltrexone in dialyzed patients. Patients (n = 8) with severe generalized pruritus received 50 mg of naltrex one orally per day for 2 weeks. The variability in the therapeutic response in treated patients required plasma concentration investigations of this o pioid antagonist. Copyright (C) 2000 John Wiley & Sons, Ltd.