Analysis of the second generation antidepressant venlafaxine and its main active metabolite O-desmethylvenlafaxine in human plasma by HPLC with spectrofluorimetric detection.

A high performance liquid chromatographic method has been developed for the determination of the recent serotonin and norepinephrine reuptake inhibitor (SNRI) venlafaxine and its main active metabolite, O-desmethylvenlafaxine, in human plasma. Separation was obtained by using a reversed phase column (C8,150×4.6mmI.D.,5m )and a mobile phase composed of75% aqueous phosphate buffer containing triethylamine at pH6.8 and 25% acetonitrile. Fluorescence detection was used, exciting at 238nm and monitoring the emission at 300nm. Citalopram was used as the internal standard. A careful pre-treatment of plasma samples was developed, using solid-phase extraction with C1 cartridges (100mg,1mL). The limit of quantitation(LOQ)was1.0ng/mL and the limit of detection (LOD) was 0.3ng/mL for both analytes. The method was applied with success to plasma samples taken from patients undergoing treatment with venlafaxine. Precision data, as well as accuracy results, were satisfactory and no interference from other drugs wa sfound. Hence,the method is suitable for therapeutic drug monitoring of venlafaxine and its main metabolite in depressed patients’ plasma.