Monitoring of tricyclic antidepressants in human serum and plasma by HPLC: characterization of a simple, laboratory developed method via external quality assessment.

A reversed-phase high performance liquid chromatography (HPLC) method for the determination of plasma and serum levels of amitriptyline (AMI), nortriptyline (NORT), imipramine (IMI), desipramine (DESI), clomipramine (CLOMI), and norclomipramine (NCLOMI) is described. The assay is based upon single step liquid/liquid extraction of these compounds using hexane at pH 11 (recovery between 92 and 105%), a Nova-Pack C-18 HPLC cartridge column, a mobile phase composed of a phosphate buffer with 50% (v/v) acetonitrile and about 0.2% (v/v) diethylamine (final pH: 8) and solute detection at 242 nm. Using 1 ml of plasma or serum and econazole as internal standard, drug levels between 20 and 400 ng ml(-1) (about 60-1450 nM) were found to provide linear calibration graphs. For drug concentrations in the range of 70-120 ng ml(-1) (about 240-430 nM), intraday and interday imprecisions (n = 5) were determined to be < 6.0, and < 15%, respectively. Data reported include those gathered over a 3-year period during which this assay was employed for therapeutic drug monitoring and clinical toxicology. The performance of the laboratory developed assay was assessed via analysis of monthly samples provided by an external quality control scheme.