Charles E. Hignite

Kinetics of R and S warfarin enantiomers

A method is reported for simultaneous measurement of the kinetics of R and S warfarin enantiomers. Pure pentadeuterated R and S enantiomers were each combined with unlabeled enantiomers to form “pseudo”‐racemic mixtures which were given (0.75 mg/kg) to 5 healthy subjects. Plasma R and S enanliomer levels were measured by gas chromatography–mass spectrometry. Elimination half‐lifes (t½s) and volumes of distribution (Vds) of the enantiomers were not altered by the presence of the other.

Lack of Effect of Aspirin on Cigarette Smoke-Induced Increase in Circulating Endothelial Cells

A random-order, double-blind crossover study was done to compare the effects of placebo and two different doses of aspirin on the endothelial cell count of venous blood before and after smoking. Each of 17 male habitual smokers with coronary artery disease smoked two cigarettes during each of three 20-min periods separated by 2 weeks. Each patient was asked to take a tablet containing 150 mg of aspirin, 300 mg of aspirin or a placebo 12 h before each experimental smoking period and to abstain from smoking in the interim. Endothelial cell counts were determined by means of differential centrifugation and phase-contrast microscopy and nicotine by gas chromatography. After ingestion of placebo, the mean endothelial cell counts (+/- SD) were 2.7 +/- 0.8 and 4.5 +/- 0.9 per counting chamber before and after smoking respectively (p less than 0.001). Endothelial cell counts and plasma nicotine concentrations were not significantly correlated. Neither the mean presmoking values nor smoking-induced changes in either variable were affected either dose of aspirin. The data suggest that smoking caused acute endothelial cell desquamation which was not prevented by aspirin.

Quantitation of lidocaine and its deethylated metabolites in plasma and urine by gas chromatography-mass fragmentography

A sensitive, precise and accurate method for simultaneous quantitation of lidocaine and its deethylated metabolites by gas chromatography-mass fragmentography has been developed. Propyl derivatives of the deethylated metabolites are formed directly in either plasma or urine by treatment with propionaldehyde and sodium cyanoborohydride. The propyl derivatives and unchanged lidocaine are extracted, separated by gas chromatography and quantitated by mass fragmentography using mepivacaine as the internal standard. Quantitation of these compounds to levels as low as 50 ng/ml body fluid has been achieved with coefficients of variation less than 10%.

Human metabolism of tolfenamic acid. I. Isolation, preliminary characterization and pharmacokinetics of tolfenamic acid and its metabolites

SummaryThe metabolic fate and pharmacokinetics of tolfenamic acid, a new anti-inflammatory agent, was studied after intravenous and oral administration of14C-tolfenamic acid to one healthy volunteer. The recovery in urine was 77% of the intravenous dose and 93% of the oral dose. About 11% of the doses was found in faeces after both routes of administration whereas no radioactivity was detected in expired air, saliva or red cells. In plasma 90–99% of the radioactive compounds were bound to proteins whereasin vitro protein-binding of tolfenamic acid was 99.7%. Tolfenamic acid was biotransformed into several metabolites and only less than 10% of the doses was excreted into urine as the glucuronide/sulphate conjugate of unchanged drug. Tolfenamic acid and four metabolites were separated by TLC, together they accounted for 90–100% of urine radioactivity. Two major metabolites with preliminary identification as hydroxylation products of tolfenamic acid were isolated in pure form for further structural analysis. After fast initial decline the total plasma radioactivity decreased slowly with a mean half life of 58 hours. The elimination rate of tolfenamic acid into urine was fast with a half life of 1.9 hours whereas the metabolites were eliminated more slowly. Their elimination showed three phases, a rapid initial phase up to six hours, second phase up to 48 hours with half lives ranging from 9 to 13 hours and a third terminal slow, quantitatively minor, phase thereafter.In conclusion, tolfenamic acid is practically completely absorbed from the GI tract, probably undergoes considerable enterohepatic circulation, is highly protein bound and extensively metabolized to several metabolites slowly excreted into urine.

Human metabolism of tolfenamic acid. II. Structure of metabolites and C-13 NMR assignments of fenamates

SummaryMetabolites of tolfenamic acid appearing in human urine have been isolated and their structures determined by C-13 nuclear magnetic resonance and gas chromatography-mass spectrometry. Comparative studies on tolfenamic, mefenamic, and flufenamic acids in conjunction with the metabolites have permitted complete C-13 NMR assignments for this series of compounds. Five metabolites identified included three that were monohydroxylated, one that was both methoxylated and hydroxylated, and another in which the methyl group was oxidized to a carboxyl group. The information presented on the fenamate standards and the metabolites represents an excellent basis for structural elucidation of other fenamates and their metabolites.

Determination of carbonyl oxygen exchange rates in α-ketoacids by gas chromatography-mass spectrometry

Abstract A method for determining the rate of exchange of the carbonyl oxygen in α-ketoglutarate using gas chromatography-mass spectrometry is described. The method is based on a new procedure for quenching the exchange reaction by rapid oxidative decarboxylation of the α-ketoacid to the next lower homologous carboxylic acid using concentrated hydrogen peroxide. Using this method the rate constant for carbonyl oxygen exchange in α-ketoglutarate in 0.1 m imidazole buffer, pH 7.5, was found to be (2.8 ± 0.2) × 10−3 s−1 at 25°C. Data obtained using this technique suggest that hydration is the mechanism for carbonyl oxygen exchange in α-ketoacids. The method is also applicable to the measurement of oxygen exchange rates of other α-ketoacids free in solution and bound in enzyme complexes.