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 concurre nt measurement of fluoxetine (FLU), norfluoxetine (NFLU), amitriptylin e (AMI), nortriptyline (NTRIP), imipramine (IMI), and desipramine (DES ) is described. Using a mixture of acetonitrile:methanol:0.056 M ammon ium acetate: 1 M ammonium hydroxide (100: 10:4.5:2.6, by volume) as mo bile phase, the compounds along with doxepin (DOX) (internal standard) were separated on a 10 mu, 8 mm x 10 cm C18 Resolve cartridge in conj unction with radial compression liquid chromatographic module, and wer e 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% ph osphoric acid prior to injection. Under these conditions, no interfere nce in the assay was observed, and the retention times of NFLU, DOX, F LU, AMI, IMI, NTRIP, and DES were 7.8, 11.6, 16, 17.8, 20.9, 31, and 3 5 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 simultane ously measure these drugs in patients and to investigate their steady- state pharmacokinetics when used in combination.