Oxidative one-carbon cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes.

1. The oxidative one-carbon cleavage reaction in the octyl side chain of olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide], a new potent biguanide antiseptic, was characterized in dog liver microsomes. 2. Olanexidine was initially biotransformed to a monohydroxylated metabolite, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-2-octanol (DM-215), and DM-215 was subsequently oxidized to the diol derivative, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-1,2-octandiol (DM-220). DM-220 was further biotransformed to 2-hydroxy aldehyde derivative, 2-hydroxy carboxylic acid derivative, and an oxidative C-1-C-2 bond cleavage metabolite, 7-[5-(3,4-dichlorobenzyl)-1-biguanidino] heptanoic acid [DM-223 (C7), a seven-carbon chain derivative], after incubation with dog liver microsomes. 3. DM-223 formation required NADPH as a cofactor and was inhibited by quinidine and quinine, relatively selective inhibitors of CYP2D subfamilies in dogs. 4. The results suggest that the one-carbon fragment of the octyl side chain of olanexidine could be removed by the oxidative C-C bond cleavage with the possible involvement of cytochrome P450 systems such as CYP2D subfamily. This oxidative C-C bond cleavage reaction by cytochrome P450s could play an important role in the removal of one-carbon fragment of other drugs or endogenous compounds containing aliphatic chains.

Involvement of cytochrome P450 in the metabolism of rebamipide by the human liver.

1. The metabolism of rebamipide, a gastroprotective agent, was investigated using human liver microsomes and cDNA-expressed human cytochrome P450 systems. 2. 6-Hydroxy and 8-hydroxyrebamipide were produced by human cytochrome P450 enzyme(s), and 8-hydroxylation was the major metabolic pathway. K(m) and V(max) for 8-hydroxylation were 1.35 +/- 0.20 mM and 0.32 +/- 0.34 nmol min(-1) mg protein(-1), respectively (mean SD, n = 6). Kinetic analysis showed that the 8-hydroxylation reaction consisted of a single component. 3. 8-Hydroxylation was inhibited by the addition of CYP3A4 antibodies as well as troleandomycin, a specific inhibitor of CYP3A4. Furthermore, the metabolism of rebamipide in human liver microsomes was compatible with that in a human cDNA-expressed CYP3A4 system, but not for other human P450 expression systems. It is therefore suggested that the hydroxylation of rebamipide only involves CYP3A4. 4. Rebampide showed no inhibitory effect on CYP1A2-, 2C9-, 2C19-, 2D6-, 2E1- and 3A4-catalysed metabolism. In addition, the metabolic contribution by CYP3A4 was considered to be slight for the overall elimination of rebamipide in man. It is therefore considered that drug interactions with cytochrome P450 enzymes are not involved in either the metabolism of rebamipide or the metabolism of other drugs concomitantly administered with rebamipide.

Fluoroquinolone concentrations in plasma, urine, and bile after oral administration in rats with renal failure: useful technique for long-term bile collection.

Using a previously reported technique for bile collection, we studied the pharmacokinetics of levofloxacin (LVFX) and grepafloxacin (GPFX) in normal rats and in animals with renal failure. Continuous bile drainage was performed using normal and renal-failure Wistar rats. Oral GPFX or LVFX (40 mg/Kg) was administered. The drug concentrations in plasma, urine, and bile were determined by high-performance liquid chromatography. The area under the blood concentration-time curve (AUC) in each renal-failure rat was calculated. There were no significant differences in GPFX concentrations in the serum, urine, and bile between the renal-failure and normal rats, but the LVFX level in the urine of the renal-failure group was statistically significantly lower than in the normal group. The AUC of GPFX had an opposite correlation with the degree of renal failure, but that of LVFX was correlated.

In vitro characterization of the oxidative cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes.

The metabolism of olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide], a new potent biguanide antiseptic, was investigated in dog liver microsomes to characterize the enzyme(s) catalyzing the biotransformation of olanexidine to C-C bond cleavage metabolites. Olanexidine was initially biotransformed to monohydroxylated metabolite 2-octanol (DM-215), and DM-215 was subsequently oxidized to diol derivatives threo-2,3-octandiol (DM-221) and erythro-2,3-octandiol (DM-222). Diols were further biotransformed to a ketol derivative and C-C bond cleavage metabolite (DM-210, hexanoic acid derivative), an in vivo end product, in the incubation with dog liver microsomes. The formations of DM-215, DM-221, DM-222, and DM-210 followed Michaelis-Menten kinetics, and Eadie-Hofstee analysis of the metabolite formation activity confirmed single-enzyme Michaelis-Menten kinetics. The K(m) and V(max) values for the formation of DM-210 appeared to be 2.42 microM and 26.6 pmol/min/mg in the oxidation of DM-221 and 2.48 microM and 30.2 pmol/min/mg in the oxidation of DM-222. The intrinsic clearance (V(max)/K(m)) of the C-C bond cleavage reactions was essentially the same with either DM-221 or DM-222 as substrate. These oxidative reactions were significantly inhibited by quinidine, a selective inhibitor of CYP2D subfamilies, indicating the metabolic C-C bond cleavage of the octyl side chain of olanexidine to likely be mediated via the CYP2D subfamily in dog liver microsomes. This aliphatic C-C bond cleavage by cytochrome P450s may play an important role in the metabolism of other drugs or endogenous compounds possessing aliphatic chains.

Oxidative cleavage of the octyl side chain of 1-(3,4-dichlorobenzyl)-5-octylbiguanide (OPB-2045) in rat and dog liver preparations.

The metabolism of 1-(3,4-dichlorobenzyl)-5-octylbiguanide (OPB-2045), a new potent biguanide antiseptic, was investigated using rat and dog liver preparations to elucidate the mechanism of OPB-2045 metabolite formation, in which the octyl side chain is reduced to four, five, or six carbon atoms. Chemical structures of metabolites were characterized by 1H NMR, fast atom bombardment/mass spectrometry, and liquid chromatography/electrospray ionization-tandem mass spectrometry. Three main metabolites were observed during incubation of OPB-2045 with rat liver S9: 2-octanol (M-1), 3-octanol (M-2), and 4-octanol (M-3). In the incubation of OPB-2045 with dog liver S9, eight metabolites were observed, seven of which being M-1, M-2, M-3, 2-octanone (M-4), threo-2,3-octandiol (M-5), erythro-2,3-octandiol (M-6), and 1,2-octandiol (M-7). M-5 and M-6 were further biotransformed to a ketol derivative and C-C bond cleavage metabolite (hexanoic acid derivative), an in vivo end product, in the incubation with dog liver microsomes. The reactions required NADPH as a cofactor and were significantly inhibited by the various inhibitors of cytochrome P450 (i.e., CO, n-octylamine, SKF 525-A, metyrapone, and alpha-naphthoflavone). The results indicate that the degraded products of OPB-2045 are produced by C-C bond cleavage after monohydroxylation, dihydroxylation, and ketol formation at the site of the octyl side chain with possible involvement of cytochrome P450 systems. This aliphatic C-C bond cleavage by sequential oxidative reactions may play an important role in the metabolism of other drugs or endogenous compounds that possess aliphatic chains.

Phenacetin deacetylase activity in human liver microsomes: distribution, kinetics, and chemical inhibition and stimulation.

Microsomal and cytosolic phenacetin deacetylase activities were examined in human liver and kidneys. Kinetic properties of the activities were also studied in human liver microsomes. Phenacetin deacetylase activity was predominantly localized in the liver microsomal fraction. The specific activities of phenacetin deacetylation in liver cytosol and in kidney microsomes and cytosol were all less than 5% of that in liver microsomes. In human liver microsomes, Eadie-Hofstee plots for phenacetin deacetylation were monophasic, indicating a single-enzyme catalytic reaction. The Michaelis-Menten parameters, K(m) and V(max), for the deacetylation were 4.7 mM and 5.54 nmol/min/mg of protein, respectively. The intrinsic clearance, calculated as V(max)/K(m), was 1.18 microl/min/mg of protein. Although the organophosphate bis(4-nitrophenyl)phosphoric acid markedly inhibited the reaction in human liver microsomes, the activity has a tolerance to the treatment of phenylmethylsulfonyl fluoride, a serine hydrolase inhibitor. Prazosin, a peripheral alpha(1)-adrenergic antagonist, noncompetitively inhibited the phenacetin deacetylation with a K(i) value of 19.0 microM. Flutamide, a nonsteroidal androgen receptor antagonist, stimulated the activity by up to 349%. This increase was accompanied by a decrease in the K(m) value and no change in the V(max) value, resulting in an increase in the intrinsic clearance by up to 700% of the control. These results suggest that the phenacetin deacetylase localized in human liver microsomes has not only a catalytic site but also a negative and/or positive modulation site or sites.

Proteases involved in the metabolic degradation of human interleukin-1beta by rat kidney lysosomes.

The in vitro metabolic degradation of human interleukin (IL)-1beta was studied using lysates of rat kidney lysosomes, and proteases involved in the degradation were identified. In the study of IL-1beta degradation, fluorescein isothiocyanate (FITC)-labeled IL-1beta was used as a substrate. The maximal degradation of IL-1beta occurred at pH 3.0, and the reaction was proportional to the lysosomal protein concentration and time of incubation. The degradation was stimulated by the addition of L-cysteine. The reaction was not inhibited by phenylmethanesulfonyl fluoride or EDTA, indicating that serine proteases or metalloproteases do not play a major role in the degradation process. N-Ethylmaleimide, leupeptin and E-64, inhibitors of thiol protease, inhibited the degradation of IL-1beta, by 59%-70%. Pepstatin A, an inhibitor of carboxyl protease, inhibited the degradation by 58%. Combinations of thiol and carboxyl protease inhibitors nearly completely inhibited the degradation. Bio-Gel P-10 gel filtration chromatography of in vitro reactants confirmed the ability of lysosomal proteases to degrade IL-1beta and revealed four to five peaks of degradation products. Taken together, these results indicate that thiol protease and carboxyl protease play an important role in the IL-1beta degradation process by kidney lysosomes. Leupeptin and E-64 dose dependently inhibited both cathepsin B and cathepsin L activities, and pepstatin A strongly inhibited cathepsin D activity in rat kidney lysosomes. The present results suggest that cathepsin B, cathepsin L, and cathepsin D in kidney lysosomes are involved in the metabolic degradation of human IL-1beta.

Cytochrome P-450 isoforms involved in carboxylic acid ester cleavage of Hantzsch pyridine ester of pranidipine.

Cytochrome P-450 (CYP) isoforms responsible for the cleavage of Hantzsch pyridine ester at the 3-position of pranidipine were studied in vitro using cDNA-expressed human CYP enzymes. CYP1A1, 1A2, 2D6, and 3A4 cleaved the ester with a catalytic activity of 5.5, 0. 93, 13.1, and 22.4 nmol/30 min/nmol P-450, respectively. CYP2A6, 2B6, 2C8, 2C9, 2C19, and 2E1 were not involved in the de-esterification. The Km and Vmax values for the de-esterification were 11.8 microM and 0.47 nmol/min/nmol P-450 in the CYP2D6-catalyzed reaction and 8. 7 microM and 0.84 nmol/min/nmol P-450 in the CYP3A4-catalyzed reaction. The intrinsic clearance (Vmax/Km) of the de-esterification by CYP3A4 was 2-fold greater than that by CYP2D6. Quinidine almost completely inhibited the CYP2D6-mediated de-esterification at the concentration of 1 x 10(-6) M. Ketoconazole and troleandomycin inhibited the CYP3A4-mediated reaction in a dose-related manner. The results indicate that although the multiple CYP isoforms can catalyze the de-esterification, CYP3A4 and 2D6 are the major isoforms.

High-performance liquid chromatography-electrospray tandem mass spectrometry for the measurement of 1-(3,4-dichlorobenzyl)-5-octylbiguanide in human serum.

1-(3,4-dichlorobenzyl)-5-octylbiguanide (OPB-2045) is a new biguanide antimicrobial agent currently in clinical use as a topical bactericidal antiseptic. A method combining high-performance liquid chromatography (HPLC) with electrospray ionization (triple and quadruple stage) tandem mass spectrometry (ESI-MS/MS) was developed to quantify OPB-2045 in human serum. Solid phase extraction was performed on 0.2 ml of sample to ensure a high level of sensitivity before HPLC-ESI-MS/MS analysis. The limit of quantitation for the method was set at 0.05 ng/ml. Intra-assay and interassay precision were less than 13.7%, with a deviation from the expected value of no greater than 10.5% at a concentration range of 0.05 ng/ml to 5 ng/ml. Decomposition of OPB-2045 in human serum did not occur after storage for 15 months at -20 degrees C, even after three repetitions of freezing and thawing. Application of this method was demonstrated in a pharmacokinetic study of OPB-2045 in healthy patient subjects after a single topical application of 5 g/L preparation of its liquid formulation.

Metabolism of 1-(3,4-dichlorobenzyl)-5-octylbiguanide in the dog.

1. The biotransformation of 1-(3,4-dichlorobenzyl)-5-octylbiguanide (OPB-2045), a new potent biguanide antiseptic, was investigated in male beagle dogs. Urinary and faecal excretion of unchanged compound and metabolites were studied following a single subcutaneous injection of 14C-labeled compound at a dose of 1 mg/kg. 2. Four urinary metabolites were structually identified using synthetic standards and/or spectral data as 3,4-dichlorobenzoic acid, 6-[5-(3,4-dichlorobenzyl)-1-biguanidino] hexanoic acid (DM-210), 4-[5-(3,4-dichlorobenzl)-1-biguanidino] butanoic acid (DM-212) and 5-[5-(3,4-dichlorobenzyl)-1-biguanidino] pentanoic acid (DM-213). 3. The predominant radioactive substances in the excreta were DM-213 and DM-210 at 26.1% and 25.5%, respectively, of the dose. No unchanged compound was detected in the urine, and in the faeces it was only 2% of the dose.

Biotransformation of the novel inotropic agent toborinone (OPC-18790) in rats and dogs. Evidence for the formation of novel glutathione and two cysteine conjugates.

The metabolism of toborinone, (+/-)-6-[3-(3,4-dimethoxybenzylamino)-2-hydroxypropoxy]-2(1H)-quin - olinone, a novel inotropic agent, was studied in rats and dogs after intravenous administration. Chemical structures of the 13 metabolites were characterized by direct-probe FAB/MS and field desorption/MS, LC/FAB/MS, and various NMR measurements. After intravenous dosing of 10 mg/kg [14C]toborinone, fecal and urinary recoveries of the 14C dose were approximately 70% and 26-30%, respectively, in both rats and dogs. The predominant component of radioactivity was the unchanged toborinone in every biological specimen in rats and dogs. Although unchanged toborinone was predominantly observed, toborinone underwent extensive conjugations with glucuronic acid, sulfate, and glutathione, either directly or following phase I reaction. Metabolites resulting from oxidative N-C cleavage were minor both in number and in quantity in every biological specimen in rats and dogs. In rats, toborinone underwent O-demethylation to form M-7 and successive phase it reaction to yield the glucuronide M-1 and the sulfoconjugate M-2, and deconjugation to yield M-7, which was a primary metabolite accounted for 35.67% of the radioactivity excreted in the feces by 48 hr. Conjugates M-1 and M-2 were the major metabolites in rat plasma. In dogs, toborinone was metabolized via mercapturic acid pathway to yield the primary metabolites, cysteine conjugates M-10 and M-11 that accounted for 19.10% and 6.70% of the radioactivity excreted in the feces by 48 hr and that were detected species specifically in dogs. The glutathione conjugate M-13, which was isolated from in vitro incubations using dog liver, led us to consider a possible mercapturic acid pathway from the parent compound to M-10. Metabolites in dog plasma and those in urine in both rats and dogs were minor in quantity. The metabolic pathways of toborinone in rats and dogs are proposed herein.

Oxidation of diclofenac to reactive intermediates by neutrophils, myeloperoxidase, and hypochlorous acid.

Diclofenac is associated with a low, but significant, incidence of hepatotoxicity and bone marrow toxicity. It has been suggested that this could be due to a reactive acyl glucuronide. An alternative hypothesis is that an oxidative reactive metabolite could be responsible for such reactions and such metabolites formed by the enzymes present in neutrophils could be responsible for bone marrow toxicity. Others had reported the formation of 2,2'-dihydroxyazobenzene during the oxidation of diclofenac by myeloperoxidase/hydrogen peroxide. In contrast, in similar experiments we did not find evidence for the formation of 2,2'-dihydroxyazobenzene, but we did find several products, including a reactive iminoquinone. The same iminoquinone was formed by the oxidation of 5-hydroxydiclofenac. This iminoquinone was also formed by oxidation of diclofenac by HOCl or by activated neutrophils. It reacted with glutathione to form a conjugate. 5-Hydroxydiclofenac is also a major hepatic metabolite of diclofenac, and we found that rat hepatic microsomes oxidized 5-hydroxydiclofenac to the iminoquinone which was trapped with glutathione. This reactive metabolite represents another possible cause of the idiosyncratic reactions associated with the use of diclofenac.

Mammary excretion and placental transfer of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1,3-dioxolane] platinum(II) in rats.

The mammary excretion and placental transfer of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1,3-dioxolan e] platinum(II) (CAS 146665-77-2, SKI 2053R), a new potential anticancer agent, were investigated in the lactating or pregnant rats after a single intravenous administration of 14C-SKI 2053R (20 mg/kg, 100 microCi/kg). The radioactivity of the milk declined in a biexponential fashion with an initial half-life of 0.39 h and with a terminal half-life of 14.05 h in the lactating rats. The radioactivity of the milk was lower than that of plasma until 1 h after dosing, but was higher than that of plasma from 4 h after dosing. 14C-SKI 2053R was well distributed to most tissues including uterus and placenta in the pregnant rats, but the levels of radioactivity in the amniotic fluid and fetuses were markedly lower than that in the maternal plasma. Therefore, it is concluded that SKI 2053R scarcely passes the blood-placenta barrier, which was confirmed by the whole-body autoradiography study.

Pharmacokinetics of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1, 3-dioxolane]platinum(II) in rats.

The blood concentration-time profile, distribution, and excretion of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1, 3-dioxolane]platinum(II) (CAS 146665-77-2, SKI 2053R), a new potential anticancer agent, were investigated in rats after intravenous administration of 14C-SKI 2053R. After a single intravenous administration, the radioactivity of blood declined in a biexponential fashion with the initial half-lives of 0.42 h and 0.37 h and with the terminal half-lives of 68.67 h and 64.67 h in male and female rats, respectively. Radioactivity was distributed very rapidly and extensively into all tissues except the central nervous system. The major amount of the radioactivity was found in the gastrointestinal contents, urine, and organs of elimination at all time points. The distribution pattern of 14C-SKI 2053R observed by the measurement of tissue concentrations was in accordance with that observed by whole-body autoradiography. The 0-7 days cumulative urinary and fecal recoveries of total radioactivity after a single dose were 83.0 +/- 4.5 (mean +/- S.D.) and 11.3 +/- 1.0% in male rats and 85.1 +/- 2.6 and 11.3 +/- 2.3% in female rats, respectively, resulting in total recoveries of 94.3 +/- 3.6% in male rats and 96.3 +/- 1.1% in female rats. The 0-24 h cumulative excretions of total radioactivity in the bile after a single dose were 8.7 +/- 0.4 and 15.8 +/- 3.5% in male and female rats, respectively, showing a significant sex difference.

[Induction of protective immune responses by a chimeric soluble protein from a recombinant BCG vector candidate vaccine to HIV-1].

We have been isolated HIV strains from blood specimens of HIV infected individuals in Japan for these 6 years. The number of specimens tested reached approximately 1,700 that ninety percent of them were from hemophiliacs repeatedly injected blood products from the United States. More than 300 of field HIV were successfully isolated from the samples. The isolation rates has decreased to 30 percent in 1993 from 40 percent in 1992, suggesting that treatment with anti-HIV drugs such as AZT and/or ddI may be effective to HIV-infected individuals. Further, both of the viral and genomic sequences of HIV were classified to be clade B virus. The clinical isolates that expressed IHIGPGRAFY sequence at the center of the HIV-V3 domain were found to be neutralized by an anti-clade B-V3 monoclonal antibody, mu 5.5. By individual levels, when asymptomatic seropositives have progressed to disease-states, neutralization core motif of GPGR in approximately 6% of the viruses has changed to GPGG and hydrophilic amino acid changed to hydrophobic amino acid, correlating the loss of binding activity to PND-peptide of Japanese Consensus virus. Further, rapid progressors to HIV-induced diseases showed decreased activity of the binding antibody. By using the Japanese consensus sequence of HIV-1, we successfully constructed chimeric protein secretion vectors by selecting an appropriate insertion site of a carrier protein, and established the PND-peptide secretion system in BCG. The recombinant BCG inoculated guinea pigs were initially screened by delayed-type hypersensitivity (DTH) skin reactions to the PND peptide followed by passive transfer of the DTH by the systemic route.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of intravenous OPC-18790 in humans: a novel nonglycosidic inotropic agent.

OPC-18790, a nonglycosidic intropic agent, is now under clinical development for treatment of congestive heart failure. Two separate studies (one placebo-controlled) were conducted to evaluate its pharmacokinetics and pharmacodynamics after intravenous administration to a total of 36 healthy male subjects. The drug was administered both rapidly as a .05-, .1-, .2-, or .4-mg/kg intravenous dose, and as a 1-hour infusion of .5, 1.0, 2.5, 5.0, 10.0, or 15.0 micrograms/kg/minute. Echocardiograms (ECHO) were evaluated before and immediately and 4 hours after the rapid administrations. Blood pressure (BP), heart rate (HR), and QTc in the electrocardiogram also were monitored in the rapid administration study. OPC-18790 was generally well tolerated by all subjects. Maximum peak plasma concentration and area under the curve increased linearly with dose in both studies. The t1/2, total body clearance of drug from plasma (CL), and the dose fraction excreted unchanged in the urine (fe) were comparable and dose-independent at the doses tested in both studies. The overall mean values of t1/2 alpha, t1/2 beta, CL, and fe were .08 +/- .01 hours, 3.64 +/- .22 hours, .46 +/- .01 L/kg, and 43.5 +/- 1.0%, respectively. Echocardiograms showed that, immediately after rapid administration of up to .4 mg/kg, OPC-18790 increased left cardiac function dose-proportionally (P < .05 to .01): the ejection fraction by 21.1% and fractional shortening by 26.5% compared with the predose values, blood pressure, heart rate, and QTc did not differ between subjects given OPC-18790 and these receiving placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselective high-performance liquid chromatographic assay for the determination of OPC-18790 enantiomers in human plasma and urine.

A high-performance liquid chromatographic assay method for the quantification of OPC-18790 enantiomers in human plasma and urine is described. A human plasma or urine was extracted with organic solvent under alkaline conditions following the addition of internal standard. The enantiomers and internal standard were then derivatized by reaction with the chiral reagent GITC (2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate), followed by octadecylsilica chromatographic separation of the diastereomeric products. The mobile phase consisted of acetonitrile-water (41:59). The fluorescence of the eluate was monitored at 355/405 nm. The lowest quantification limit of each enantiomer was 10 ng/ml in plasma and 0.1 micrograms/ml in urine. Both intra- and inter-day coefficients of variation were below 10%. The assay is sensitive, specific and applicable for stereoselective pharmacokinetic studies in human.

Pharmacokinetics, safety, and pharmacologic effects of OPC-21268, a nonpeptide orally active vasopressin V1 receptor antagonist, in humans.

The pharmacokinetics, safety, and pharmacologic effects of OPC-21268, a nonpeptide orally active vasopressin V1 receptor antagonist, have been investigated in 33 healthy subjects. First, 24 subjects were randomly divided into 3 groups of 8, 6 of whom were given 2 ascending single oral doses out of 6 (10, 50, 150, 300, 450, and 600 mg) of OPC-21268 after an overnight fast. The remaining two subjects in each group received placebo as control at each dosing. Additionally, after this procedure, the 6 subjects who received 50-mg single doses were given the same dose in a nonfasting condition. After the single-dose study was completed and the safety and tolerability were ascertained, the remaining 9 subjects, including 3 controls, were given 300 mg of the drug 3 times daily for 7 days (days 3-9) and were given single 100-mg oral doses before (day 1) and after (day 10) this repeated-dose study. OPC-21268 plasma concentrations declined in a monoexponential or biexponential pattern after reaching the maximum plasma concentrations (Cmax). The mean (+/- standard error of the mean) plasma half-life (t1/2) of the alpha phase ranged from 1.31 +/- 0.11 to 1.78 +/- 0.15 hours, and the mean t1/2 of the beta phase ranged from 4.31 +/- 0.28 to 6.28 +/- 0.59 hours. The area under the concentration (AUC0-infinity) and Cmax were proportional to the dose (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of a new positive inotropic agent, 3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)- quinolinone (OPC-8212) in the rat, mouse, dog, monkey and human.

1. After OPC-8212 was orally given to rats, mice, dogs, monkeys and humans, its metabolites were identified by n.m.r. and mass spectrometry, and their concentrations in the plasma, urine and faeces of these species were measured by high-performance liquid chromatography (h.p.l.c.). 2. Hydrolysis of the amide group, oxidation and cleavage of the piperazine ring, O-demethylation of the methoxy group, and conjugation were proposed as metabolic pathways of OPC-8212. 3. In rats, mice and monkeys given OPC-8212 orally, metabolites M-1 to M-6 were detected in the plasma, urine and faeces, while M-1, -4, -5 and M-6 were detected in dogs, and M-1, M-3, M-4, M-5 and M-6 were detected in humans. 4. Conjugates of metabolites M-6 and M-7, with glucuronic acid and sulphuric acid, were observed in the urine of rats and humans.