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.

1. Conjugated metabolites were isolated from the urine of patients receiving amitriptyline treatment using a combination of solid-phase extraction, h.p.l.c. and t.l.c. 2. By n.m.r. and mass spectrometry, N-glucuronides of E- and Z-10-hydroxyamitriptyline and of trans-10,11-dihydroxyamitriptyline were identified in addition to the previously described O-glucuronides of E- and Z-10-hydroxyamitriptyline and -nortriptyline and amitriptyline-N-glucuronide. 3. The quaternary ammonium glucuronides proved to be resistant to acid hydrolysis, but could be cleaved enzymatically. 4. In urine samples from three patients, 35-60% of conjugated 10-hydroxyamitriptyline was found in the form of N-glucuronides. 5. A volunteer given an i.v. infusion of amitriptyline-N-glucuronide excreted E- and Z-10-hydroxyamitriptyline-N-glucuronide; following ingestion of E-10-hydroxyamitriptyline its N-glucuronide could be measured in urine.

There is a great deal of current interest in the role and importance of chirality in the development of new drugs, but little attention is being paid to the stereochemistry of older drugs. Indeed, many older chiral drugs were introduced without adequate information on their stereochemical identity or composition. We have examined one such drug, the antihypertensive diuretic agent cyclothiazide. Standard sources of drug information and the research literature do not provide data on the stereochemical composition of clinically used cyclothiazide, although scattered reports indicate that the drug may consist of "several stereoisomers." Inspection of the chemical structure of the drug, 6-chloro-3,4-dihydro-3-(5-norbornen-2-yl)-2H-1,2,4-benzothiadiazin e-7- sulfonamide 1,1-dioxide, shows that it can exist as eight stereoisomers that may form four racemates. Using synthesis, fast-atom-bombardment mass spectrometry, gas-liquid chromatography, chiral and nonchiral high-performance liquid chromatography, and nuclear magnetic resonance spectroscopy, we determined that pharmaceutical cyclothiazide is in fact a mixture of the eight stereoisomers in the form of the four racemates. The two racemates with endo configuration at the norbornene moiety predominate over the exo racemates, and small but significant differences in isomer distribution between different batches of the drug were observed. We urge that in studies of older drugs the stereochemical details be considered.

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