Determination of fluoxetine and its N-desmethyl metabolite in human plasma by high-performance liquid chromatography

A rapid and sensitive high-performance liquid chromatographic method has been developed for the simultaneous determination of the antidepressant fluoxetine and its active metabolite norfluoxetine in human plasma using paroxetine as internal standard. After liquid–liquid extraction, the compounds were separated on a C18 column using as mobile phase acetonitrile and 40 mM potassium dihydrogen phosphate buffer (pH 2.3) in the ratio 31:69 (v/v). The quantification of fluoxetine and norfluoxetine was made by fluorescence detection at Ex/Em 230/312 nm. The assay for each analyte was linear over the ranges 1–39 and 0.9–36 ng/ml, respectively. For both compounds intra- and inter-day accuracy and precision ranged between −7.9–12.4 and 0.7–14.7%, respectively. The method was applied to the analysis of plasma samples obtained from healthy subjects treated with one single oral dose of 40 mg fluoxetine.