Sensitive, high-throughput gas chromatographic–mass spectrometric assay for fluoxetine and norfluoxetine in human plasma and its application to pharmacokinetic studies

Abstract

A sensitive, robust gas chromatographic–mass spectrometric assay suitable for use in pharmacokinetic or bioequivalence studies is presented for the selective serotonin reuptake inhibitor, fluoxetine, and its major metabolite, norfluoxetine ( N-desmethylfluoxetine). This method employs solid-phase extraction followed by acetylation with trifluoroacetic anhydride and analysis of the derivatives using selected ion monitoring. The lower limit of quantification was 1.0 ng/ml, and the assay was linear for both analytes from 1 to 100 ng/ml. Mean recoveries following solid-phase extraction at concentrations of 5.0, 20 and 100 ng/ml were 91% (fluoxetine) and 87% (norfluoxetine). Assay precision (as mean RSD) and accuracy (as mean relative error) for both analytes were tested at the same three nominal concentrations and were found to be within 10% in all cases. Analysis of fluoxetine concentrations in plasma samples from 18 volunteers following administration of a single 40 mg dose of fluoxetine provided the following pharmacokinetic data (mean±SD): C max, 32.73±9.21 ng/ml; AUC 0–∞, 1627±1372 ng/ml h; T max, 3.08 h (median); k e, 0.022±0.007 h −1; elimination half-life, 37.69±21.70 h.