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 40mM 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 230/312nm. The assay for each analyte was linear over the ranges 1-39 and 0.9-36ng/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 40mg fluoxetine.