CONCURRENT LIQUID-CHROMATOGRAPHIC MEASUREMENT OF FLUOXETINE, AMITRIPTYLINE, IMIPRAMINE, AND THEIR ACTIVE METABOLITES NORFLUOXETINE, NORTRIPTYLINE, AND DESIPRAMINE IN PLASMA

An expedient and specific liquid chromatographic method for a concurrent measurement of fluoxetine (FLU), norfluoxetine (NFLU), amitriptyline (AMI), nortriptyline (NTRIP), imipramine (IMI), and desipramine (DES) is described. Using a mixture of acetonitrile:methanol:0.056 M ammonium acetate: 1 M ammonium hydroxide (100: 10:4.5:2.6, by volume) as mobile phase, the compounds along with doxepin (DOX) (internal standard) were separated on a 10 mu, 8 mm x 10 cm C18 Resolve cartridge in conjunction with radial compression liquid chromatographic module, and were detected in the effluent spectrophotometrically at 220 nm. A hexane:isoamyl alcohol (98:2, by volume) solution was used for extraction of plasma and the drugs were removed from the organic phase with 0.03% phosphoric acid prior to injection. Under these conditions, no interference in the assay was observed, and the retention times of NFLU, DOX, FLU, AMI, IMI, NTRIP, and DES were 7.8, 11.6, 16, 17.8, 20.9, 31, and 35 min, respectively. The assay was highly linear (r > 0.994), and the within- and between-day coefficient of variance was consistently less-than-or-equal-to 9.8%. This assay is currently being used to simultaneously measure these drugs in patients and to investigate their steady-state pharmacokinetics when used in combination.