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Perhexiline is a drug that is used for treatment of moderate to severe angina pectoris that has not responded to other treatment. It has a low therapeutic index, and saturable metabolism that is also subject to genetic polymorphism (CYP2D6). Concentration monitoring of the parent drug and its major metabolite is considered necessary to optimise efficacy and reduce the risk of hepatotoxicity and neuropathy. A rapid, simple and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) assay was developed for the determination of perhexiline and its metabolite cis-hydroxyperhexiline in human plasma. After proteins were precipitated with acetonitrile, perhexiline, the major metabolite cis-hydroxyperhexiline and nordoxepin as the internal standard were resolved on a phenyl-hexyl column using gradient elution of 0.05% formic acid and methanol. The three compounds were detected using electrospray ionisation in the positive mode. Standard curves were linear over the concentration range 10-2000microg/L (r>0.999), bias was

A sensitive method for the simultaneous determination of doxepin and its active metabolite desmethyldoxepin in plasma was established, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted with hexane-isoamyl alcohol, separated on a Phenomenex Luna C18 5 microm, 150x2.1 mm column with a mobile phase consisting of methanol-water-formic acid (600:400:0.5, v/v) at a flow-rate of 0.25 ml/min. Detection was achieved by a Perkin-Elmer API 2000 mass spectrometer at unit resolution in multiple reaction monitoring mode monitoring the transition of the protonated molecular ions m/z 280.2, 266.2 and 250.1 to the product ions m/z 107.1, 107.1 and 191.0 for analyte, metabolite and internal standard (benzoctamine-HCl), respectively. TurbolonSpray ionisation was used for ion production. The mean recovery for doxepin and desmethyldoxepin was 90% and 75%, respectively, with a lower limit of quantification at 0.320 ng/ml and 0.178 ng/ml for the analyte and its metabolite, respectively, using 0.5 ml plasma for extraction. This is the first assay method described for the simultaneous determination of doxepin and desmethyldoxepin in plasma using LC-MS-MS. The method is sensitive enough to be used in drug bioavailability studies with doxepin.

A stereoselective method of analysis of the antidepressant drug doxepin (DOX, an 85:15% mixture of E-Z stereoisomers), its principal metabolites E- and Z-N-desmethyldoxepin (desDOX) and ring-hydroxylated metabolites in microsomal incubation mixtures is described. DOX and its metabolites were extracted from alkalinised incubation mixtures by either: 9:1 hexane-propan-2-ol (method 1) or 1:1 hexane-dichloromethane (method 2), derivatised with trifluoroacetic anhydride and analysed by GC-MS with selected ion monitoring. Both methods were suitable for the analysis of individual desDOX isomers as indicated by correlation coefficients of > or = 0.999 for calibration curves constructed between 50 and 2500 nM, and good within-day precision at 125 nM (C.V. < or = 14%) and 1000 nM (C.V. < or = 8%). Method 1, however, was unsuitable for the analysis of ring-hydroxylated metabolites of DOX, whereas the hydroxylated metabolites of E-DOX and E-desDOX (generated in situ) were extracted by method 2 with a C.V. of ca. 13%. This is the first assay method that permits the simultaneous measurement of desDOX and hydroxylated metabolites of DOX in microsomal mixtures.

Doxepin is a tricyclic antidepressant marketed as an irrational mixture of cis- and trans-geometric isomers in the ratio of 15:85. A convenient high-performance liquid chromatographic (HPLC) procedure for simultaneous quantitation of geometric isomers of doxepin and N-desmethyldoxepin in plasma and urine is described. The HPLC procedure employed a normal phase system with a silica column and a mobile phase consisting of hexane-methanol-nonylamine (95:5:0.3, v/v/v), a UV detector and nortriptyline as the internal standard. The liquid-liquid extraction solvent was a mixture of n-pentane-isopropanol (95:5, v/v). The limit of quantitation was 1 ng/ml for each isomer. The calibration curves were linear over the ranges 1-200 ng/ml (plasma) and 1-400 ng/ml (urine). In plasma, the accuracy (mean +/- S.D.) (97.53 +/- 1.67%) and precision (3.89 +/- 1.65%) data for trans-doxepin were similar to corresponding values for urine, i.e., 97.10 +/- 2.40 and 3.82 +/- 1.14%. Accuracy and precision data for trans-N-desmethyldoxepin in plasma were 97.57 +/- 2.06 and 4.38 +/- 3.24%, and in urine were 97.64 +/- 3.32 and 5.26 +/- 1.83%, respectively. Stability tests under three different conditions of storage indicated no evidence of degradation. The recovery of doxepin was 61-64% from plasma and 63-68% from urine. The method has been applied to analyses of plasma and urine samples from human volunteers and animals dosed with doxepin.

A simultaneous method for the therapeutic monitoring of amitriptyline, doxepin, imipramine, and their active demethylated metabolites nortriptyline, nordoxepin, and desipramine, respectively, in plasma or serum by reversed-phase liquid chromatography (RPLC) is presented. The drugs and the internal standard (loxapine) are first extracted from 2 ml of serum into butylchloride at pH 14, and then back extracted into 200 microliter of 0.025 mol/l hydrochloric acid. An aliquot of the aqueous acid phase is injected into the chromatograph and eluted with acetonitrile-phosphate buffer (21: 79, by vol.) containing 0.6 nl of n-nonylamine per liter of phosphate buffer. The drugs are eluted in a total chromatographic time of approximately 13 min at ambient temperature and detected at 200 nm. A sensitivity of 5 microgram/l of serum for each drug is obtained. Recoveries for these drugs ranged from 77% to 103%; and the coefficient of variation (day-to-day) ranged from 4.2 to 7.8. Of 35 basic or neutral drugs tested for possible interference, only propoxyphene interferes with the analysis of nortriptyline.

A GLC method for the simultaneous quantitative determination of the cis- and trans-isomers of doxepin and desmethyldoxepin in human plasma was developed. The method involves the use of a capillary column for efficient separation of the four compounds and the internal standards, amitriptyline and nortriptyline. A high sensitivity is obtained with a nitrogen detector, enabling quantitation of the compounds in plasma of humans treated chronically with doxepin. Confirmation of the identity of the cis- and trans-isomers of doxepin and desmethyldoxepin in biological samples was carried out by selected ion monitoring.

The theromdynamic pKa values for doxepin and its metabolite desmethyldoxepin were determined by the solubility method to be 8.96 and 9.75, respectively at 25 degrees. The intrinsic solubilities for doxepin and desmethyldoxepin were linearly dependent upon ionic strength. The intrinsic solubilities at zero ionic strength and 25 degrees were determined to be 1,13 x 10(-4) M for doxepin and 3.95 x 10(-4) M for desmethyldoxepin. The solubility experiment was repeated at different temperatures and a constant ionic strength of 0.167 M. The change in enthalpy (6.71 kcal/mole) and entropy (-4.16 cal/mole degrees K) of solution for doxepin was determined from a van't Hoff plot for this nonideal system. The apparent partition coefficient between hexane and water for the doxepin free base was determined to be 13,615 at an ionic strength of 0.067 M.

Two chromatographic methods, high-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC) were compared for sensitivity and reproducibility in the analysis of the tricyclic antidepressant doxepin and its metabolite, desmethyldoxepin, in plasma. The HPLC procedure yielded a better reproducibility, as reflected by the coefficient of variation, and a higher sensitivity, as reflected by the minimum detectable quantity. The application of these methods for therapeutic and subtherapeutic monitoring of plasma levels of the drug is described.