Liquid-phase microextraction and desorption electrospray ionization mass spectrometry for identification and quantification of basic drugs in human urine

Hollow fibre liquid-phase microextraction (LPME) and desorption electrospray ionization mass spectrometry (DESI-MS) were evaluated for the identification and quantification of basic drugs in human urine samples. The selective extraction capabilities of three-phase LPME provided a significant reduction in the matrix effects otherwise observed in direct DESI-MS analysis of urine samples. Aqueous LPME extracts (in 10 mM HCl) were deposited on porous Teflon, dried at room temperature, and the dried spots were then analyzed directly with DESI-MS in full scan mode. Pethidine, diphenhydramine, nortriptyline, and methadone were used as model compounds for identification, and their limits of identification were determined to be 100, 25, 100, and 30 ng/mL, respectively. In a reliability test with 19 spiked urine samples, 100% of the positive samples containing the model drugs in concentrations at or above the limit of identification were identified. Diphenhydramine was used as a model compound for quantitative analysis with diphenhydramine-d(5) as an internal standard. The calibration curve was linear in the range 50-2000 ng/mL (R(2) = 0.992) with a limit of quantification at approximately 140 ng/mL. The intra- and inter-day relative standard deviations were <9.5%. In a reliability test with six spiked urine samples, deviations between the measured and the true values for diphenhydramine were in the range 0.2-22.9%.

Sample preparation with fiber-in-tube solid-phase microextraction for capillary electrophoretic separation of tricyclic antidepressant drugs in human urine

Solid-phase microextraction (SPME) is a solvent-free sample preparation technique using a thin coating attached to the surface of a fused silica-fiber as the extraction medium, which has been successfully applied to the analysis of a wide variety of compounds by coupling to gas chromatography (GC). In recent years, in-tube SPME using GC capillary column as the extraction medium has also been developed and coupled with liquid chromatography (LC) for the preconcentration of nonvolatile compounds. In this study, an on-line interface between the fiber-in-tube SPME and capillary electrophoresis (CE) has been developed, and the preconcentration and separation of four tricyclic antidepressant (TCA) drugs, amitriptyline, imipramine, nortriptyline, and desipramine, were performed with the hyphenated system. Under the optimized condition, a better extraction performance than conventional in-tube SPME was obtained, even the length of the extraction medium was much shorter. The results clearly indicated that the fiber was working effectively as an extraction medium. For the separation of these four TCAs, capillary electrophoretic separation with beta-cyclodextrin as the buffer additive has been employed and the application of the developed system to the analysis of complex sample mixtures in a biological matrix is also demonstrated.

Time course of enzyme induction in humans: effect of pentobarbital on nortriptyline metabolism

To study the effect of induction we gave six male volunteers 10 mg nortriptyline three times a day for 4 weeks and 0.2 gm pentobarbital on days 8 to 21. Plasma and urinary levels of nortriptyline and metabolites were measured. The rate and extent of induction of the enzyme(s) were estimated by a model with use of nortriptyline concentrations. There was a marked decrease of nortriptyline levels after 2 days of pentobarbital treatment. Total clearance of nortriptyline increased more than twofold (range, 1.6-fold to 4.1-fold). Apparent metabolic clearance by 10-hydroxylation increased markedly. The decrease in nortriptyline levels was more rapid than the increase after pentobarbital cessation, fitting with the theory of the model. The induction of nortriptyline metabolism is probably mainly the result of an increase in a non-CYP 2D6 P450 isozyme, possibly CYP 3A4 or a CYP 2C form. More knowledge of induction characteristics of drugs should lead to better predictions of decreased effects and appearance of adverse effects. The kinetic model used for analysis of our data could then be useful.

Possible markers for postmortem drug redistribution

The possibility that postmortem biochemical changes in blood might parallel drug redistribution and thus serve as markers was explored in a detailed case study. Eighteen blood and 14 tissue and fluid samples were taken at autopsy 16 h after the death of a 34-year-old female from amitriptyline overdose. Ranges of drug concentrations in blood were amitriptyline 1.8 to 20.2 micrograms/mL, nortriptyline 0.6 to 7.3 micrograms/mL, levels were lowest in femoral vein and highest in pulmonary vein blood. Corresponding levels of 17 amino acids showed markedly different patterns of site-to-site variability. There was a strong positive correlation between individual amino acid and drug concentrations in pulmonary blood samples (n = 5), particularly for glycine, leucine, methionine, serine, and valine. In blood samples from the great veins and right heart (n = 10), the correlation was less strong (r = 0.6 to 0.7). Methionine showed a strong positive correlation in pulmonary samples (r = 0.93), and negative correlation in great veing samples (r = -0.68). Lactic acid showed a strong negative correlation in pulmonary samples (r = -0.93) but a positive correlation in great vein samples (r = 0.71). Alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, gamma-glutamyl transferase, glucose, and bilirubin had a weak positive correlation with drug levels in great vein samples but not pulmonary samples. The results suggest that hepatic enzymes are relatively poor markers for postmortem hepatic drug shifts but that amino acids, particularly methionine, may be useful markers for pulmonary drug shifts.

Enantioselective amitriptyline metabolism in patients phenotyped for two cytochrome P450 isozymes

In 26 hospitalized patients with depression, a combined pharmacogenetic test with dextromethorphan, a substrate of cytochrome P450IID6, and mephenytoin, the S-form of which is hydroxylated by a P450IIC isozyme, was carried out before amitriptyline therapy. Metabolites were determined in 24-hour urine samples collected on treatment day 8, and the contributions of individual compounds, including the four isomers of 10-hydroxyamitriptyline and 10-hydroxynortriptyline to total excretion were calculated. Formation of (-)-E-10-hydroxyamitriptyline and (-)-E-10-hydroxynortriptyline apparently depends on the activity of cytochrome P450IID6 because negative correlations existed between the log metabolic ratio of dextromethorphan and the relative quantities of these enantiomers. In contrast, correlations were positive for nortriptyline, (+)-E-10-hydroxynortriptyline, (-)-Z-10-hydroxynortriptyline, and (+)-Z-10-hydroxynortriptyline. The mephenytoin hydroxylase seems to participate in side-chain demethylation to the secondary and primary amines, because the log metabolic ratio of mephenytoin correlated negatively with the relative quantity of E-10-hydroxydidesmethylamitriptyline and positively with that of amitriptyline and its N-glucuronide.

Column switching and high-performance liquid chromatography in the analysis of amitriptyline, nortriptyline and hydroxylated metabolites in human plasma or serum

A column-switching system for the direct injection of plasma or serum samples, followed by isocratic high-performance liquid chromatography and ultraviolet detection, is described for the simultaneous quantitation of the tricyclic antidepressant amitriptyline, its demethylated metabolite nortriptyline and the E- and Z-isomers of 10-hydroxyamitriptyline and 10-hydroxynortriptyline. The method included adsorption of amitriptyline and metabolites on a reversed-phase C8 clean-up column (10 microns; 20 mm x 4.6 mm I.D.), washing of unwanted material to waste and, after on-line column-switching, separation on a cyanopropyl analytical column (5 microns; 250 mm x 4.6 mm I.D.). The compounds of interest were separated and eluted using acetonitrile-methanol-0.01 M phosphate buffer (pH 6.8) (578:188:235, v/v) within less than 20 min. Various drugs frequently co-administered with amitriptyline or other antidepressants did not interfere with the determinations. In plasma samples spiked with 25-300 ng/ml, the recoveries were between 84 and 112% and the inter-assay coefficients of variation were 3-11%. After a minor modification, as little as 5 ng/ml could be quantitated. There were linear correlations (r greater than 0.99) between drug concentrations of 5-500 ng/ml and the detector signal. The method allows routine measurements of amitriptyline, nortriptyline and hydroxylated metabolites in blood plasma or serum of patients treated with amitriptyline or nortriptyline, and enables the results to be reported within 1 h.

Stereoselective inhibition of nortriptyline hydroxylation in man by quinidine

1. Four volunteers phenotyped as extensive metabolizers of sparteine took 25 mg nortriptyline hydrochloride and collected urine for 72-80 h. Total free and conjugated 10-hydroxynortriptyline (10-OH-NT) accounted for 54-58% of the dose and it was reduced to 25-40% when 50 mg quinidine sulphate was ingested on the first and second day. 2. Of the four isomers of 10-OH-NT, (-)-E-10-OH-NT was selectively decreased in quantity by quinidine coadministration, while the (+)-isomer and (-)- and (+)-Z-10-OH-NT were found in unchanged or slightly increased quantities. The contribution of (-)-E-10-OH-NT to total E-10-OH-NT and the E-/Z-ratio in total 10-OH-NT were significantly reduced. 3. The quantity of the phenol, 2-hydroxynortriptyline in urine was decreased by quinidine; the relative amounts of metabolites with a primary amino group were not affected. 4. Liver microsomes from a donor in which cytochrome P450IID6 was shown to be present by in vitro phenotyping metabolized NT to E-10-OH-NT containing 86% of the (-)-isomer. Quinidine reduced the hydroxylation rate in (-)-E-10-position much more than that in (+)-E-10-position. 5. Since quinidine selectively impairs the function of cytochrome P450IID6, it is concluded that this isoform catalyses NT hydroxylation predominantly in (-)-E-10- and in 2-position.

Enantioselective hydroxylation of nortriptyline in human liver microsomes, intestinal homogenate, and patients treated with nortriptyline

The enantioselectivity of hydroxylation of nortriptyline (NT) to E-10-hydroxynortriptyline (E-10-OH-NT) was studied in human liver microsomes, intestinal homogenate, and patients treated with NT. The rate of formation of (-)-E-10-OH-NT was higher than that of (+)-E-10-OH-NT both in the liver microsomes and in the intestinal homogenate. Quinidine, a prototype competitive inhibitor of the cytochrome P450IID6 ("debrisoquin hydroxylase"), inhibited the formation of (-)-E-10-OH-NT in a concentration-dependent manner in liver microsomes, while the formation of (+)-E-10-OH-NT was hardly affected. This indicates that P450IID6 catalyzes the hydroxylation of NT in a highly enantioselective manner to (-)-E-10-OH-NT in the liver. Another P450 isozyme besides IID6 seems to be responsible for the formation of the (+)-enantiomer in the liver. In intestinal homogenate, the formation of both enantiomers of E-10-OH-NT was inhibited to about the same extent by quinidine, the maximum inhibition being much less than in the liver. In the urine of six patients treated with NT, the (-)-enantiomer accounted for 91 +/- 2% of the unconjugated E-10-OH-NT, and for 78 +/- 6% of the glucuronide conjugates. The study shows that NT is hydroxylated in a highly enantioselective way, probably catalyzed by the polymorphic P450IID6, to (-)-E-10-OH-NT both in vitro in human liver as well as in vivo in patients treated with the drug.

[Plasma and urine kinetics of amitriptyline oxide and its metabolites. Comparison of intravenous infusion and oral administration in volunteers]

The study objective was to obtain detailed information on the plasma and urine kinetics of amitriptylinoxide (CAS 4317-14-0) and its metabolites. For this reason, 60 mg of amitriptylinoxide was administered to 12 subjects, both by intravenous infusion and by oral dosage, in a study performed according to a randomized two-way cross-over design. In plasma, we succeeded in analyzing the metabolites amitriptyline and nortriptyline in addition to the parent substance amitriptyloxide. The tests for the parent substance amitriptylinoxide revealed maximum plasma levels of 721 and 686 ng/ml at 1.96 h (i.v. infusion) and 0.82 h (oral formulation), respectively. Mean values of 2331 (infusion) and 1714 h.ng/ml (oral formulation) were determined for the area under the curve from time 0 to infinity AUC (0-infinity). We also produced a comprehensive evaluation of amitriptyline, however, this was not possible for the metabolite nortriptyline. In urine, we succeeded in a reliable quantification of 4 metabolites, namely cis-OH-amitriptylinoxide, trans-OH-amitriptylinoxide, amitriptyline and OH-nortriptyline, in addition to the parent substance amitriptylinoxide. In individual samples, nortriptyline, cis-OH-amitriptyline and trans-OH-amitriptyline were additionally identified. In the course of the study, there were no reports or observations of any adverse reactions in addition to the side effects known for amitriptylinoxide from literature. There were no clinically relevant differences in tolerability observed between these two preparations.

Use of the EMITtox serum tricyclic antidepressant assay for the analysis of urine samples

The EMITtox serum tricyclic antidepressant (TCA) assay is intended for use with serum or plasma. Currently, there are no commercially available immunoassay kits available for the detection of TCAs in urine. The proposed method utilizes the EMITtox serum TCA assay for the direct analysis of urine samples. The minimum detectable concentration of nortriptyline in urine is 25 ng/mL. The within-run CV was determined to be 0.6% and the between-run CV was 2.6%. The TCA assay cross-reacts with phenothiazines and antihistamines. The proposed methodology should be applicable to other EMIT serum assays to allow their use with urine.

Nortriptyline and debrisoquine hydroxylations in Ghanaian and Swedish subjects

Eleven Ghanaian and 12 Swedish subjects phenotyped with a debrisoquine (D) hydroxylation test were given a single oral dose of nortriptyline (NT). Much the same percentage of the given NT dose was excreted as 10-hydroxy-NT (10-OH-NT) by Ghanaians (43.1%) and Swedes (49.2%). There was a close correlation between plasma clearance of NT by 10-hydroxylation and the D metabolic ratio (D/4-OH-D in urine) in the Ghanaians (rs = -0.95; P less than 0.01) and Swedes (rs = -0.84; P less than 0.01). The E-isomer of 10-OH-NT is the major isomer in both Ghanaians (76% to 92% of total 10-OH-NT) and Swedes (78% to 95%). It is suggested that the E-10-hydroxylation of NT and the 4-hydroxylation of D are similarly coregulated in Ghanaians and Swedes.

Amitriptyline and its basic metabolites determined in plasma by gas chromatography

Gas chromatography was used to determine plasma levels of amitriptyline, nortriptyline and their 10-hydroxy derivatives after conversion to the dehydro compounds by heating with acid. The primary amine 10-hydroxydesmethylnortriptyline is also dehydrated and the dehydro compound coincides on the chromatogram with dehydronortriptyline. Treatment of the extract with salicylaldehyde selectively removed the primary amine, which was determined by difference. Cis- and trans-hydroxydesmethylnortriptyline were isolated from urine by thin-layer chromatography and used to standardize the estimation. The stability of all the metabolites in plasma was investigated. Results are given for hydroxydesmethylnortriptyline levels in the plasma of 41 patients treated with amitriptyline.

Effect of simultaneous treatment with low doses of perphenazine on plasma and urine concentrations of nortriptyline and 10-hydroxynortriptyline

Plasma levels of nortriptyline and perphenazine were measured in six patients on continuous nortriptyline treatment before, during and after oral administration of perphenazine 4 mg t.i.d. In four patients the plasma levels of the conjugated and unconjugated principal metabolite 10-hydroxynortriptyline were also measured. Urinary excretion of conjugated and unconjugated 10-hydroxynortriptyline and plasma levels of perphenazine were determined in all six patients. During treatment with perphenazine two patients showed a slight increase in the plasma level of nortriptyline. The changes in metabolite excretion rate were inconclusive. Thus, there did not appear to be any important pharmacokinetic interaction between the two drugs at the doses used, which were normal therapeutic doses. The previously reported inhibitory effect of perphenazine on the metabolism of nortriptyline probably depended therefore, either on administration of a higher dose of perphenazine, or on treatment in the reverse sequence--a single dose of nortriptyline was given to patients already receiving perphenazine.

First-pass metabolism of nortriptyline in man

The kinetics of nortriptyline were studied after oral and intravenous (iv) administration of test doses of 50 mg 14C-nortriptyline. The systemic availability of orally administered nortriptyline varied from 0.46 to 0.59 in 6 subjects. The decrease in availability was due to metabolism after administration. Systemic clearance varied from 0.31 to 0.66 L/min. From these measurements indirect estimates of the hepatic blood flow could be made, and a variation from 0.6 to 1.5 L/min was found. Quantitative measurements of first-pass metabolism could also be obtained from urinary metabolite excretion data when the kinetics of metabolite formation and elimination were taken into account. From the second or third day after the test dose, the urinary excretion rate of total radioactivity declined monoexponentially with half-lives closely corresponding to the plasma half-lives of unchanged nortriptyline. Analysis of the data from the iv test according to a 2-compartment open model showed that there was a close correlation between the rate constant of distribution from central to peripheral compartment (k12) and the elimination rate constant in the central compartment (kel). Still, there was some variation in the kel/k12-ratio, and this variation corresponded to the variation of the estimated hepatic blood flow.

Drug interaction: inhibitory effect of neuroleptics on metabolism of tricyclic antidepressants in man

Total urinary excretion of radioactivity after oral or intravenous administration of a test dose of (14)C-imipramine was measured in eight patients. They were tested before, during, and after treatment with neuroleptics. Excretion diminished while the patients were being treated with perphenazine, haloperidol, or chlorpromazine, though not during flupenthixol treatment.Total urinary excretion of radioactivity and plasma levels of metabolites and unchanged drug were measured in five patients after a test dose of (14)C-nortriptyline. Each patient was tested before and again during perphenazine treatment. In all patients perphenazine treatment caused: (1) decrease of total urinary excretion, (2) decreased plasma level of metabolites, and (3) increased plasma level of unchanged nortriptyline.These results indicate that neuroleptics inhibit the metabolism of tricyclic antidepressants in man.