Quantitative analysis of amitriptyline and nortriptyline in human plasma and liver microsomal preparations by high-performance liquid chromatography

A simple, rapid, highly selective and sensitive method for the analysis of amitriptyline and nortriptyline in plasma and human liver microsomes is described. It is suitable for the routine analysis of large numbers of samples using readily available instrumentation and low cost consumables. The detection limit was 2 ng/ml for both compounds and calibration curves were linear over a wide range of concentrations and passed through the origin. The within-batch and between-batch coefficients of variation for amitriptyline and nortriptyline were less than 7.4% and 12.8%, respectively. A series of compounds, including inhibitors used for probing cytochrome P450 activity in vitro, were tested for interference in the assay. Only ketoconazole caused interference and the assay was modified to allow samples containing ketoconazole to be analysed.