[14C]7-ethoxycoumarin metabolism by precision-cut rat hepatic slices.

The metabolism of [14C]7-ethoxycoumarin ([14C]7-EC) has been studied in rat liver slice cultures in vitro by using a direct radiometric high-pressure liquid chromatography method. [14C]7-EC was extensively biotransformed in these incubations to 7-hydroxycoumarin (7-OHC), 7-hydroxycoumarin glucuronide, and 7-hydroxycoumarin sulfate, as well as to a large number of previously unrecognized metabolites, the majority of which are sulfate conjugates. The liver slice [14C]7-EC metabolite profile was also very complex and seemed to be qualitatively similar to the medium metabolite profile. Quantitative comparisons, however, demonstrated that there was approximately two to five times more 7-OHC in the liver slice than in the medium, whereas 7-hydroxycoumarin sulfate, the most abundant metabolite in the medium, was present only at low levels in the liver slice. These data demonstrate that 7-OHC levels are considerably underestimated when only levels in the medium are considered. Total metabolite levels were approximately equal in the medium and liver slice after a 2-hr incubation, with considerably higher total metabolite levels present in the medium at the end of the incubation period (8 hr). Additional studies are needed to identify the structures of the previously unrecognized metabolites observed in this study and the enzymes responsible for their formation, as well as studies to define the metabolism of [14C]7-EC in other in vitro models by using tissue from humans and other animal species.

The metabolic disposition of oxazepam in rats.

The metabolic fate of oxazepam in the rat is more complex than in larger animal species. Condensation of the diazepinyl ring and phase 1 transformations which lead presumedly via an epoxide to metabolites hydroxylated on the 5-phenyl moiety of oxazepam occurs in addition to glucuronidation, which has often been reported to be predominant in larger species. Unchanged oxazepam is the major compound in plasma, liver, and kidney, but phase 1 and phase ii metabolites also are found. In brain, though, only oxazepam is recognized, and a brain/plasma ratio of approximately 3-5:1 demonstrates that the drug has considerable affinity for that tissue. Excretion of oxazepam and its biotransformation products occurs mainly by the fecal route (70.7 +/- 6.0% of the dose) via biliary secretion. Glucuronides and sulfates of the hydroxylated metabolites and oxazepam and its glucuronide are secreted into bile, but only oxazepam, 4'-hydroxyoxazepam, and unknown polar metabolites constitute most of the fecal radioactivity, suggesting that enterohepatic circulation and intestinal metabolism are significant in the rat.

Determination of ciramadol in plasma by gas-liquid chromatography.

An analytical method for determining ciramadol concentrations in plasma was developed and evaluated for its specificity, precision, linearity, and sensitivity. GLC-electron capture detection of a dipentafluorobenzoyl derivative of the drug was used for quantitation. An isomer of the drug served as an internal standard. Resulting mean ratios of the peak height of derivatized drug to that of derivatized internal standard varied with a coefficient of variation that ranged from 3.8 to 11.1%. The mean ratio was linearly related to ciramadol content (8.75-175 ng) with a correlation coefficient greater than to 0.999. The minimum quantifiable concentration was 4 ng/ml with a 2-ml specimen. An application of this method is presented.

Species-related differences in the stereoselective glucuronidation of oxazepam.

The concentrations of (R)-(-)- and (S)-(+)-oxazepam glucuronides in plasma and urine of several species have been measured. The relative amounts of these diastereoisomers vary among species. Thus, in the plasma and urine of rhesus monkeys the concentrations of the R-isomer are higher, whereas in man and dog more of the S-isomer is present. In plasma and urine of miniature swine the amounts of the two diastereoisomers are about equal. In the urine of rabbits the S-isomer prevails. Similar species-related differences are observed in the in vitro formation of the isomeric oxazepam glucuronides. Homogenates of dog, miniature swine, rabbit, and rat liver produce more of the S-isomer, whereas with monkey liver the formation of (R)-oxazepam glucuronide is favored. The agreement between in vivo and in vitro data is fairly good for rhesus monkey, miniature swine, and rabbit. However, for the dog the ratio of S- to R-isomers in the liver homogenate is much higher than in plasma and urine. This species-dependent stereoselective glucuronidation of oxazepam is not related to the phylogenetic or dietary grouping of these species.

Pharmacokinetics of parenteral dezocine in rhesus monkeys and dogs.

Pharmacokinetic parameters of the analgesic, dezocine, were determined after intravenous and intramuscular injection (1 mg/kg) to rhesus monkeys and dogs. In both species, the drug was rapidly distributed after intravenous administration and then eliminated with a mean half-life of 2.4 hr. Systemic clearance was 54.8 +/- 8.6(SD) and 65.8 +/- 14.0(SD) ml/min/kg in the rhesus monkey and dog, respectively. Glucuronidation was recognized as a major metabolic pathway in both species, and sulfate conjugation was indicated in the dog. Renal elimination of dezocine was minimal. Less than 4% of the dose was eliminated as unchanged dezocine in urine of rhesus monkeys and 1% of the dose in dog urine. After im administration, release from the injection site was rapid and no metabolism at the injection site was indicated. Multiple-dose experiments in dogs did not reveal accumulation. The acquisition of data was made possible by the development of a sensitive, specific assay, which depends on gas-liquid (electron capture) chromatography of a pentafluorobenzoylated derivative of dezocine.

Metabolic disposition of ciramadol in rhesus monkeys and rats.

Studies on the metabolic disposition of ciramadol, a new orally effective analgesic, have been conducted in the rhesus monkey and male rat. The drug is well absorbed but undergoes extensive presystemic metabolism when given by the intragastric route (1 mg/kg) to rhesus monkeys. Maximum concentrations in plasma do not exceed 4 ng/ml. The major transformation occurs by glucuronidation and leads to two metabolites, and aryl O- and an alicyclic O-glucuronide. Phase I transformations are apparently minor and include N-demethylation, formation of benzoxazinyl metabolites from the reaction of endogenous acetaldehyde and formaldehyde with N-desmethylciramadol, and oxidation of the alicyclic and aromatic rings. Mass-spectrometric analyses of the isolated glucuronides and the minor phase I metabolites have been employed for structural assignments. Excretion of the intragastric dose occurs predominantly by the renal route. When given intramuscularly (1 mg/kg), concentrations of ciramadol peak at 1150 ng/ml by 0.5 hr after medication and decline rapidly to less than 7 ng/ml by 8 hr. Approximately 10% of the dose is excreted as unchanged ciramadol after im dosing. In male rats, the drug is absorbed rapidly after single 1-mg/kg intragastric doses and is taken up notably by liver, lung, kidney and spleen. Unlike its disposition in rhesus monkeys, ciramadol is present in plasma and excreted into urine mainly in the unconjugated form. Concentrations of drug in rat plasma are higher than those in rhesus monkey plasma, suggesting a smaller first-pass effect in the rat.

The metabolic disposition of dezocine in rhesus monkeys and female rats given 14C-dezocine intragastrically.

The metabolic disposition of 14C-dezocine has been investigated in male rhesus monkeys and female rats given intragastric 1- and 5- mg/kg doses, respectively. In both species the dose appeared to be rapidly and extensively absorbed. Concentrations of radioactivity were detected in monkey plasma 15 min after drug administration (the earliest sampling time) and reached a peak between 0.5 and 2 hr, whereas in the rat, high concentrations of radioactivity were detected in plasma and most tissues at 15 min. Biliary secretion was extensive in the monkey, but in the monkey as well as in the rat, the ultimate excretion of the radioactive dose was primarily through renal elimination. Tissue uptake of unconjugated drug was extensive in both species, and concentrations of drug in brain were substantially higher than those in plasma. Metabolism was mainly by glucuronidation in both species and also by sulfate formation in the female rat. Two minor imine metabolites produced by N-oxidation were indicated after a comparison with synthetic standards.

The disposition of [14C]iprindole in man, dog, miniature swine, rhesus monkey and rat.

1. Absorption of a single oral dose of [14C]iprindole was rapid in rats, rhesus monkeys, miniature swine, dogs and human volunteers. In all species except the rat, most of the radioactivity in the blood resided in the plasma. Small amounts of unchanged iprindole were detected in the plasma of rats and rhesus monkeys but not in man and miniature swine. 2. Radioactivity was excreted mainly in the urine of man, miniature swine and rhesus monkey, but in the faeces of rat and dog. 3. Urinary radioactivity was associated with basic (free and conjugated), acidic and highly polar, water soluble metabolites. At least 20 metabolites as well as small amounts of unchanged drug were detected in the basic fractions of each species' urine. 4. Many of these metabolites were common to all species; however, qualitative as well as quantitative differences were apparent. Mass-spectrometric analysis of several metabolites indicated N-demethylation and oxidation of the alicylic ring or a combination of both pathways.

Diastereoisomeric glucuronides of oxazepam. Isolation and stereoselective enzymic hydrolysis.

Oxazepam glucuronide isolated from swine urine by previously published methods was separated into its diastereoisomers by ion-exchange chromatography on a preparative scale. Quantitative high-performance liquid chromatography was used to monitor the separation. The two isomers were obtained in analytically pure form and then characterized by elemental analysis, oxazepam content, mass spectrometry, ultraviolet spectroscopy, optical rotation and optical rotatory dispersion-circular dichroism. The latter permitted the assignment of the dextrorotatory and the levorotatory isomers to the (S)- and (R)- configurations, respectively. Rates of enzymic hydrolysis depend on the configuration of the substrate as well as on the enzyme preparation used. Rate of cleavage was highest with the (S)-(+)-glucuronide and beta-glucuronidase from Escherichia coli. This enzyme possesses the highest degree of stereoselectivity; it hydrolyzes the (S)-(+)-isomer more than 400 times faster than the (R)-(-)-form. Bovine liver glucuronidase is less stereoselective, whereas glucuronidase preparations of molluscan origin exhibit little stereoselectivity. The ready hydrolysis of one of the glucuronides by an enzyme from an intestinal microorganism may play a role in the enterohepatic circulation of oxazepam.