Haruo Tachizawa

Stereoselective metabolic disposition of enantiomers of ofloxacin in rats

1. Stereoselective metabolic disposition of ofloxacin (OFLX) was studied in rats after oral administration of S-(-)-14C-OFLX and R-(+)-14C-OFLX at a dose of 20 mg/kg. 2. Radioactivity of the S-(-)-isomer was eliminated from blood much faster than that of the R-(+)-isomer. Marked differences in pharmacokinetic parameters exist between the enantiomers; the half life and AUC values of R-(+)-OFLX were greater than those of S-(-)-OFLX. Enantiomeric differences were also seen in the excretion of radioactivity, especially in biliary excretion. 3. 31.3 and 7.4% dose were excreted in the 8 h bile as ester glucuronides after oral administration of S-(-)- and R-(+)-OFLX, respectively. The enantiomeric difference in biliary excretion may be caused by stereoselective glucuronidation of S-(-)-OFLX to the ester glucuronide. 4. The metabolite pattern in serum and urine showed that the ester glucuronide of S-(-)-OFLX was more predominant than that of R-(+)-OFLX. 5. The stereoselective ester glucuronidation of the S-(-)-isomer in rats may induce significant differences in the pharmacokinetic parameters of S-(-)- and R-(+)-OFLX.

Species-related stereoselective disposition of ofloxacin in the rat, dog and monkey.

1. The stereoselective disposition of ofloxacin (OFLX) was studied in rats, dogs and monkeys after oral administration of racemic OFLX. 2. In rats serum concentrations of (R)-(+)-OFLX were much greater than those of (S)-(-)-OFLX, which is the active form of OFLX. In monkeys, by contrast, serum concentrations of (S)-(-)-OFLX predominated over (R)-(+)-OFLX levels. In dogs there were no differences in AUC or Cmax between the enantiomers. Thus, there exists a species-related difference in the stereoselective disposition of OFLX. 3. In rats the stereoselective differences were mainly due to stereoselective glucuronidation; OFLX is hardly metabolized in dogs, monkeys and humans. 4. In monkeys the AUC of (S)-(-)-OFLX was increased by co-administration of the (R)-(+)-form, indicating that the stereoselectivity of OFLX disposition in monkeys may be caused by competition between the enantiomers for renal excretion, especially for renal tubular secretion.

Isolation and identification of metabolites of ofloxacin in rats, dogs and monkeys

Metabolites of (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H -pyrido [1,2,3-de][1,4]benzoxazine-6-carboxylic acid (ofloxacin) in excreta of rats, dogs and monkeys after oral administration of 14C-ofloxacin (20 mg/kg) were isolated and identified. Three metabolites of ofloxacin were detected in the excreta of all three species, and identified by t.l.c., u.v., n.m.r. and mass spectrometry as follows: M-1, ester glucuronide of ofloxacin; M-2, unchanged ofloxacin; M-3, (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(1-piperazinyl)-7-oxo-7H-pyrido [1,2,3-de][1,4]benzoxazine-6-carboxylic acid (desmethyl ofloxacin); M-4, (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H -pyrido [1,2,3-de][1,4]-benzoxazine-6-carboxylic acid piperazine-4-oxide (ofloxacin N-oxide). It is concluded that ofloxacin is metabolized by O-acyl glucuronidation, N-demethylation and N-oxidation.

Lack of Effect of Ofloxacin on Theophylline Pharmacokinetics in Rats

Effect of ofloxacin, a new quinolone antibacterial agent, on the pharmacokinetics of theophylline was studied in rats in comparison with that of enoxacin and cimetidine. Ofloxacin by pretreatment with five oral doses of 50 mg/kg did not increase serum concentrations of theophylline (5 mg/kg, i.v. single) and showed no significant effect on total body clearance, serum half-life (T1/2) and AUC of theophylline, while enoxacin by the same pretreatment increased significantly serum theophylline concentrations and resulted in significant effect on all the pharmacokinetic parameters. Coadministration of ofloxacin (80 mg/kg, p.o. twice) did not induce a significant effect on the pharmacokinetic parameters of theophylline at repeated doses (50 mg/kg, i.v., twice daily for 3 days). On the contrary, coadministration of enoxacin and cimetidine at the same dose as ofloxacin remarkably increased serum concentrations of theophylline at the same repeated doses, and caused a significant decrease in clearance and an increase in T1/2 and AUC. The three drugs had no influence on rat serum protein binding of theophylline. Ofloxacin exhibited a weak inhibitory effect on rat hepatic microsomal cytochrome P-450-dependent monooxygenases, whereas enoxacin and cimetidine induced a significant inhibition of the enzymes. Thus, it is concluded that ofloxacin has no significant effect on the pharmacokinetics of theophylline in rats, and that enoxacin raises serum theophylline concentrations and results in a significant effect on the theophylline pharmacokinetics by inhibition of the hepatic microsomal monooxygenases in rats.

Biotransformation of a new pyrrolidinone cognition-enhancing agent : isolation and identification of metabolites in human urine

1. The metabolites of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)acetamide (DMPPA; MH-1), in the urine of human volunteers have been investigated. 2. Ten metabolites together with the unchanged drug (MH-1) were isolated by h.p.l.c. and identified by n.m.r. and mass spectrometry as: three metabolites hydroxylated in the pyrrolidine ring of MH-1 (MH-2, MH-3 and MH-4), three metabolites hydroxylated in the dimethylphenyl ring of MH-1 (MH-6, MH-7 and MH-8), N-[(2,6-dimethylphenylcarbamoyl)methyl]-4-hydroxybutyrylamide++ + (MH-5), N-[(2,6-dimethylphenyl-carbamoyl)methyl]succinamic acid (MH-9), the 3-O-sulphate of MH-6 (MH-10) and the 3-O-sulphate of N-(2,6-dimethyl-3-hydroxyphenyl)-2-(5-hydroxy-2-oxo-1-pyrrolidinyl)aceta mide (MH-11). 3. DMPPA was extensively metabolized. The principal metabolic transformations were hydroxylation of the pyrrolidine ring at the C5 carbon followed by oxidative C-N cleavage, and hydroxylation of the phenyl ring followed by sulphate conjugation.

Effect of New Quinolones on Drug-Metabolizing Enzyme System of Rat Hepatic Microsomes

Effects of repeated oral administration of new quinolones, ofloxacin, enoxacin and norfloxacin, once daily for 7 days, on the drug-metabolizing enzyme system of rat hepatic microsomes were studied in comparison with that of phenobarbital, a potent inducer of cytochromes P-450. Treatment of phenobarbital at the oral dose of 120 mg/kg induced significant increases in the contents of cytochrome P-450, cytochrome b5 and NADPH-cytochrome P-450 reductase and in the activity of ethoxycoumarin O-deethylase, and significant decreases in the activities of benzphetamine N-demethylase and aniline hydroxylase. However, ofloxacin, enoxacin and norfloxacin at the oral dose levels of 80 and 320 mg/kg showed no significant effect on the content of each constituent of the drug-metabolizing enzyme system, and the three enzyme activities. Thus, it is concluded that new quinolones including ofloxacin have no ability to induce a cytochrome-P-450-dependent monooxygenase system.

High-performance liquid chromatographic determination of a new nootropic, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, in human serum and urine

A high-performance liquid chromatographic method for the determination of a novel nootropic agent, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)acetamide (DM-9384, I), in human serum and urine has been developed. Compound I and the internal standard were extracted with chloroform from alkalinized serum and urine, and the organic layer was evaporated to dryness. The residue was chromatographed on a Nucleosil 7C18 reversed-phase column using 1/15 M potassium dihydrogen-phosphate-acetonitrile (7:3, v/v) as a mobile phase. Quantitation was achieved by monitoring the ultraviolet absorbance at 210 nm. The response was linear (0-2114.0 ng/ml) and the detection limits were 30 ng/ml for serum samples and 50 ng/ml for urine samples. The utility of the assay was demonstrated by determining compound I in serum and urine samples from three healthy male subjects receiving an oral dose of 30 mg of the drug. This method is satisfactorily sensitive and accurate, and is applicable for pharmacokinetic studies of I in humans.