Determination of fluvoxamine concentration in plasma by reversed‐phase liquid chromatography

Fluvoxamine, a serotonin re-uptake inhibitor, was quantified in plasma by modifying a previously published procedure for monitoring plasma concentrations of tricyclic antidepressants. Alkalinized plasma samples were extracted with n-hexane/isoamyl alcohol, followed by back-extraction with diluted phosphoric acid. The extracts were analysed by reversed-phase liquid chromatography using a C-18 column, with phosphate/acetonitrile as the mobile phase. The assay was linear from 10 to 800 micrograms/L. Precision studies showed within-run and day-to-day coefficients of variation to be 4.5 and 6.8%, respectively. Desipramine interfered with the detection of fluvoxamine. The assay was used to measure a total of 8 plasma samples from 4 alcohol-dependent patients medicated with fluvoxamine as an adjunct to relapse prevention psychotherapy. In these patients, the plasma concentrations ranged from 54 to 241 micrograms/L. Dosage of fluvoxamine, duration of treatment, interval between last dosage and blood collection were associated with effects on plasma concentrations that were consistent with the pharmacokinetic profile of fluvoxamine.