The metabolism of (−)-(2S, 3R)-2-amino-3-hydroxy-3-(3, 4-dihydroxyphenyl) propionic acid (L-DOPS), an unphysiological amino acid and the precursor of (−)-norepinephrin (NE) was investigated in mice, rats, dogs and Rhesus monkeys after oral administration of ¹⁴C-L-DOPS labelled at C-3 position.
1. L-DOPS, (−)-(2S, 3R)-2-amino-3-hydroxy-3-(4-hydroxy-3-methoxyphenyl) propionic acid (3-OM-DOPS), 3, 4-dihydroxybenzoic acid (PA), 4-hydroxy-3-methoxybenzoic acid (VA) and their conjugates were identified as the major metabolites in urine of mice, rats, dogs and Rhesus monkeys after oral administration of ¹⁴C-L-DOPS (10 and 100 mg/kg). In addition, 3, 4-dihydroxytoluene (HC) was identified in urine of rats and Rhesus monkeys.
2. The concentration of unchanged L-DOPS in serum, liver and urine was larger than those of other metabolites. After oral administration of ¹⁴C-L-DOPS (10 mg/kg), amounts of L-DOPS, 3-OM-DOPS, PA (Conjugate) and VA (Conjugate) excreted in urine were 10 ?? 20 %, 6 ?? 15 %, 10 ?? 20 % and 2 ?? 11 % of the dose, respectively. In urine of rats and Rhesus monkeys, a trace amount of the conjugate of HC was detected.
3. Amounts of NE and its metabolite in serum and urine of amimals, after oral administrtion of ¹⁴C-L-DOPS increased evidently, in comparison with their baseline values observed before L-DOPS administration.
In every animal administered with ¹⁴C-L-DOPS, the total excretion of NE and its metabolite to urine was less than 1 % of the dose.
4. The concentration of NE in kidney of rats, after sigle oral administration of ¹⁴C-L-DOPS (10 mg/kg), was about 6 times higher than that in kidney of Rhesus monkeys.

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A GC/MS method for the determination of CS-570, a chemically stable prostacyclin analogue, was developed. This assay method was applied to study a disposition of CS-570 in dogs after a single or continuous intravenous administration. An acidified plasma, obtained from dogs, was spiked with ²H₆-CS-570 as an internal standard and extracted with reversed-phase (ODS) cartridges. After methylation with diazomethane, further purification was carried out using normal-phase (Si) cartridges. The methyl-dimethyl-iso-propylsilyl derivative of CS-570 exhibits some suitable properties in GC/MS analysis showing the intense peak at m/z (M-43) by electron ionization. At the concentration of 8 and 80 ng/ml in plasma, CV% were 2.8 and 1.7 respectively. The limit of determination is 1 ng/ml when 1 ml sample is available. Dogs were received i. v. injection of CS-570 at a single dose of 100 μg/kg or i. v. infusion at the rate of 256 and 512 ng/kg/min for 60 min. A steep and biphasic decline of CS-570 concentration in plasma was observed both after rapid injection and after the end of the infusion with half-life of approximately 10 min at β-phase. During the continuous infusion, a rapid increace of CS-570 concentration in plasma was observed and it reached 95 % of the steady-state level within 15 min. Linear relationship was obtained between doses and AUC. A metabolite, β-oxidation product, was also found in dog plasma.

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The absorption and excretion of 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)benzimidazole difumarate (KB-2413) were studied in rats and guinea pigs after oral administration of KB-2413-¹⁴C. Maximum plasma levels (C_max) appeared at 0.25 and 0.5 h after dosing in rats and guinea pigs, respectively. In rats, both C_max and the area under the plasma concentration-time curve (AUC) increased proportionally to the administered dose up to 8mg/kg.
The radioactivity excreted into the urine and the AUC after oral dosing in rats and guinea pigs were close to those after intravenous dosing, and the orally administered radioactivity was almost completely excreted into the bile and urine in the bile-duct-cannulated rats. Thus, it was suggested that KB-2413 was nearly completely absorbed from the intestinal tract of rats and guinea pigs.
The percentages of the radioactivity excreted in feces were 65.3 and 58.9 % of the dose within 96 h after oral administration of KB-2413-¹⁴C in rats and guinea pigs, respectively.
The radioactivity excreted into the bile was about 90 % of the dose within 24 h after oral dosing in bile-duct-cannulated rats. The enterohepatic circulation in rats was suggested, since a considerable amount of the radioactivity was absorbed in the rat which was administered intraduodenally with the bile collected from other rats administered with KB-2413-¹⁴C orally.

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The distribution of 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)benzimidazole difumarate (KB-2413) was studied in rats after single and multiple oral administrations of KB-2413-¹⁴C.
The radioactivity was high in the intestine, liver, pancreas and kidney, and low in the central nervous system and in the fat after single oral administration to fasted rats.
The steady-state during multiple oral administration, was reached after the 7 th dose as shown by a constant values of the tissue-to-plasma concentration ratio and AUC_0-24h.
The radioactivity excreted into both urine and feces was about 98 % within 4 d after the 14 th administration. At this time, the concentration in most tissues was lower than that at 24 h after the 1 st administration.

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The transfer of 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)benzimidazole difumarate (KB-2413) to the fetus and milk was studied in pregnant and nursing rats, respectively, after oral administration of KB-2413-¹⁴C.
The maximum level of the radioactivity in each tissue of fetal rats was reached at 2 h after dosing. At that time, the concentration in the fetus homogenate was comparable to that in the maternal plasma. The radioactivity in the fetal liver and intestine was relatively high, suggesting that the radioactivity was transfered to bile in fetuses as well as in male rats.
The radioactivity was transfered to milk after oral administration to nursing rats. Milk/plasma concentration ratios were less than 1 within 8 h. The elimination half-life of the radioactivity in milk was about 16h.

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The interaction of acetohexamide with probenecid was investigated in rabbits.
1. Probenecid significantly enhanced the hypoglycemic activity of acetohexamide after its oral administration. In addition, probenecid markedly increased the plasma concentrations of acetohexamide and its pharmacologically active metabolite, hydroxyhexamide.
2. Probenecid significantly decreased the urinary excretion of hydroxyhexamide after oral administration of acetohexamide, but caused no change in the urinary excretion of the parent compound. Probenecid non-competitively inhibited the metabolic reduction of acetohexamide by the liver cytosol.
3. Probenecid itself had little effect on the in vitro binding of acetohexamide or (−)-hydroxyhexamide to the serum, but a mutual displacement of serum protein binding was observed between acetohexamide and (−)-hydroxyhexamide.
Evidence obtained in this study suggests that the interaction of acetohexamide with probenecid is a complex process.

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We have synthesized ¹⁴C-labelled nitroglycerin (GTN) to study the blood concentration, distribution, metabolism and excretion of GTN after i. v. administration in Wistar rats.
1) The concentration of radioactivity in plasma reached the maximum level at the end of i. v. infusion for 1 hr and then it decreasedin a biexponential manner. Half lives of α and β phase were 2.59 and 28.11 hrs, respectively. The half life after repeated infusion showed the same value for α phase, but its value at β phase was increased twice as compared with single infusion. It was suggested that the metabolites of longer half life, which were formed by the repeated infusion, have circulated in a whole body for a long period at time.
2) Total excretion of radioactivity in urine, expired air and feces was about 73 % of dose during 72 hrs after a single infusion, and approximately 27 % remained in a whole body. Similar results were obtained in multiple infusion studies.
3) Urinary metabolites found during 24 hrs after administration were mono-and dinitroglycerin (GMN and GDN), glucuronide, glycerol and unknown components. One may suspect that glycerol was metabolized to ¹⁴CO₂ via the Krebs cycle.
4) The distribution of GTN in tissues and organs showed that the maximum concentration at the end of infusion or 1 hr after the end of infusion both in single and repeated administration. It decreased relatively fast until 4 hrs after the end of infusion, and thereafter a decay of concentration was quite slow. At 24 hrs after the end of infusion, remained radioactivity was 10 ?? 40 % and 40 ?? 60 % of the maximum concentration after a single and repeated infusion, respectively. This shows the accumulation of radioactivity by the repeated infusion. The entity of this accumulated subustance may be considered as the glucuronide of GDN and GMN, and glycerol which have a weak toxicity.

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Enantiomers of many drugs show differences in pharmacological activities and in metabolisms. Since such drugs are often used as racemic mixtures, it is important to determine the amounts of each enantiomer in biological fluids in order to optimize therapy and to avoid undesirable side effects. Recently, chromatographic methods have been developed for the separation of enantiomeric compounds. In principle, enantiomers are resolved in two ways.
(1) Derivatization to diastereomers with a chiral reagent followed by chromatographic separation on a nonchiral column (Indirect method).
(2) Use of a chiral mobile phase or stationary phase which forms diastereomeric complexes with the enantiomers in a column. Because of difference in their stabilities, the two enantiomers are eluted from the column at different rates (Direct method).
In this review, liquid chromatographic separation of enantiomeric drugs is described.

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