Metabolism of [(14)C]omapatrilat, a sulfhydryl-containing vasopeptidase inhibitor in humans.

Omapatrilat, a potent vasopeptidase inhibitor, is currently under development for the treatment of hypertension and congestive heart failure. This study describes the plasma profile along with isolation and identification of urinary metabolites of omapatrilat from subjects dosed orally with 50 mg of [(14)C]omapatrilat. Only a portion of the radioactivity in plasma was unextractable (40-43%). Prominent metabolites identified in plasma were S-methyl omapatrilat, acyl glucuronide of S-methyl omapatrilat, and S-methyl (S)-2-thio-3-phenylpropionic acid. Omapatrilat accounted for less than 3% of the radioactivity. However, after dithiothreitol reduction all of the radioactivity was extractable and was characterized to be omapatrilat and its hydrolysis product (S)-2-thio-3-phenylpropionic acid, both apparently bound to proteins via reversible disulfide bonds. Urinary profile of radioactivity showed no parent compound but the presence of several metabolites that can be grouped into three categories. 1) Three metabolites, accounting for 56% of the urinary radioactivity, resulted from the hydrolysis of the exocyclic amide bond of omapatrilat. Two metabolites were diastereomers of S-methyl sulfoxide of (S)-2-thio-3-phenylpropionic acid, and the third was the acyl glucuronide of S-methyl (S)-2-thio-3-phenylpropionic acid. 2) One disulfide, identified as the L-cysteine mixed disulfide of omapatrilat, accounted for 8% of the radioactivity in the urine. 3) Five metabolites, derived from omapatrilat, accounted for 30% of the radioactivity in the urine. Two of these metabolites were mixtures of diastereomers of S-methyl sulfoxide of omapatrilat and the third was the S-methyl omapatrilat ring sulfoxide. The other two metabolites were S-methyl omapatrilat and its acyl glucuronide. These results indicate that omapatrilat undergoes extensive metabolism in humans.     

Oral bioavailability and disposition of [14C]omapatrilat in healthy subjects

The objective of this study was to determine the absolute oral bioavailability and disposition of omapatrilat. This single-dose, randomized, crossover study of 20 mg intravenous and 50 mg oral [14C]omapatrilat was conducted in 12 healthy male subjects to determine the disposition and oral bioavailability of omapatrilat, an orally active vasopeptidase inhibitor. Blood samples were collected up to 120 hours, and the excreta were collected over 168 hours postdose. Plasma concentrations of omapatrilat were determined by a validated LC/MS/MS procedure. Radioactivity in blood, plasma, urine, and feces was determined by liquid scintillation counting. Urinary excretion of radioactivity averaged 80% and 64% of intravenous and oral doses, respectively; < 1% of oral dose was excreted unchanged in urine. The absolute oral bioavailability of omapatrilat averaged 31%. Total body clearance of omapatrilat (80 L/h) exceeded liver plasma flow. Apparent steady-state volume of distribution of omapatrilat (21 L/kg) was extremely high compared with total body water. Omapatrilat undergoes substantial presystemic first-pass metabolism after oral administration. Omapatrilat is eliminated primarily by metabolism, and its metabolites are eliminated primarily in urine. Extrahepatic organs may be involved in the elimination of omapatrilat. Plasma concentrations of omapatrilat exhibit a prolonged terminal elimination phase, which represents elimination from a deep compartment.     

Pharmacokinetics,metabolism and excretion of the glycine antagonist GV150526A in rat and dog

1. The pharmacokinetics, metabolic fate and excretion of 3-[-2(phenylcarbamoyl) ethenyl-4,6-dichloroindole-2-carboxylic acid (GV150526), a novel glycine antagonist for stroke, in rat and dog following intravenous administration of [C14]-GV150526A were investigated. 2. Studies were also performed in bile duct-cannulated animals to confirm the route of elimination and to obtain more information on metabolite identity. 3. Metabolites in plasma, urine and bile were identified by HPLC-MS/MS and NMR spectroscopy. 4. GV150526A was predominantly excreted in the faeces via the bile, with only trace metabolites of radioactivity in urine (< 5%). Radioactivity in rat bile was predominantly due to metabolites, whereas approximately 50% of the radioactivity in dog bile was due to parent GV150526. 5. The principal metabolites in bile were identified as glucuronide conjugates of the carboxylic acid, whereas in rat urine the main metabolite was a sulphate conjugate of an aromatic oxidation metabolite. Multiple glucuronide peaks were observed and identified as isomeric glucuronides and their anomers arising from acyl migration and muta-rotation.     

Pharmacokinetics,metabolism and excretion of the glycine antagonist GV150526A in rat and dog

1. The pharmacokinetics, metabolic fate and excretion of 3-[-2(phenylcarbamoyl) ethenyl-4,6-dichloroindole-2-carboxylic acid (GV150526), a novel glycine antagonist for stroke, in rat and dog following intravenous administration of [C14]-GV150526A were investigated. 2. Studies were also performed in bile duct-cannulated animals to confirm the route of elimination and to obtain more information on metabolite identity. 3. Metabolites in plasma, urine and bile were identified by HPLC-MS/MS and NMR spectroscopy. 4. GV150526A was predominantly excreted in the faeces via the bile, with only trace metabolites of radioactivity in urine (< 5%). Radioactivity in rat bile was predominantly due to metabolites, whereas approximately 50% of the radioactivity in dog bile was due to parent GV150526. 5. The principal metabolites in bile were identified as glucuronide conjugates of the carboxylic acid, whereas in rat urine the main metabolite was a sulphate conjugate of an aromatic oxidation metabolite. Multiple glucuronide peaks were observed and identified as isomeric glucuronides and their anomers arising from acyl migration and muta-rotation.     

Metabolism of [14C]gemopatrilat after oral administration to rats, dogs, and humans.

This study describes the pharmacokinetic parameters of gemopatrilat, a potent vasopeptidase inhibitor, in humans and the comparative biotransformation of the compound in rats, dogs, and humans after administration of a single oral dose of [14C]gemopatrilat. Gemopatrilat was rapidly absorbed in humans with an oral bioavailability of 49%. Within 5 h after dose, the mean concentrations of gemopatrilat were less than 1% of the mean Cmax values. The total area under the first-moment time curve extrapolated to infinity [AUC(INF)] value for gemopatrilat was only 2% of the AUC(INF) of radioactivity in plasma. Gemopatrilat showed a large apparent steady-state volume of distribution (2500 liters) and a prolonged terminal-phase decline in plasma concentration. These results are consistent with the idea that the free sulfhydryl group of gemopatrilat forms reversible disulfide linkages with plasma and tissue proteins and is thus eliminated from the body at a very slow rate. Approximately half of the drug-related radioactivity in 1-h plasma samples from rat, dog, and human was reduced chemically with dithiothreitol to gemopatrilat, suggesting that disulfide linkage occurred in all species. In addition, metabolites formed through S-methylation and amide hydrolysis were also detected in rat, dog, and human plasma. No gemopatrilat was detected in urine and fecal samples from all three species, indicating that the compound is extensively metabolized in vivo. The major metabolites identified in human urine and feces were also present in rat and dog. These data suggest that the metabolism of gemopatrilat in all three species were qualitatively very similar.     

Preclinical characterization of 2-[3-[3-[(5-ethyl-4'-fluoro-2-hydroxy[1,1'-biphenyl]-4-yl)oxy]propoxy]-2-propylphenoxy]benzoic acid metabolism: in vitro species comparison and in vivo disposition in rats.

Assessment of the pharmacokinetics of [14C]2-[3-[3-[(5-ethyl-4'-fluoro-2-hydroxy[1,1'-biphenyl]-4-yl)oxy]propoxy]-2-propylphenoxy-]benzoic acid ([14C]LY293111), an experimental anti-cancer agent, suggested long-lived circulating metabolites in rats. In vivo metabolites of LY293111 were examined in plasma, bile, urine, and feces of Fischer 344 (F344) rats after oral administration of [14C]LY293111. Metabolites were profiled by high-performance liquid chromatography-radiochromatography, and identified by liquid chromatography (LC)/mass spectrometry and LC/NMR. The major in vivo metabolites of LY293111 identified in rats were phenolic (ether), acyl, and bisglucuronides of LY293111. Measurement of radioactivity in rat plasma confirmed that a fraction of LY293111-derived material was irreversibly bound to plasma protein and that this bound fraction increased over time. This was consistent with the observed disparity in half-lives between LY293111 and total radioactivity in rats and monkeys, and is likely due to covalent modification of proteins by the acyl glucuronide. In vitro metabolism of [14C]LY293111 in liver slices from CD-1 mice, F344 rats, rhesus and cynomolgus monkeys, and humans indicates that glucuronidation was the primary metabolic pathway in all species. The acyl glucuronide was the most prevalent radioactive peak (16% of total 14C) produced by F344 rat slices, whereas the ether glucuronide was the major metabolite in all other species (26-36% of total 14C). Several minor hydroxylated metabolites were detected in F344 rat slice extracts but were not observed in other species. The data presented suggest that covalent modification of proteins by LY293111 acyl glucuronide is possible in multiple species, although the relative reactivity of this metabolite appears to be low compared with those known to cause adverse drug reactions.     

Excretion and metabolism of recainam, a new anti-arrhythmic drug, in laboratory animals and humans

The metabolic disposition of recainam, an antiarrhythmic drug, was compared in mice, rats, dogs, rhesus monkeys, and humans. Following oral administration of [14C]recainam-HCl, radioactivity was excreted predominantly in the urine of all species except the rat. Metabolite profiles were determined in excreta by HPLC comparisons with synthetic standards. In rodents and rhesus monkeys, urinary excretion of unchanged recainam accounted for 23-36% of the iv dose and 3-7% of the oral dose. Aside from quantitative differences attributable to presystemic biotransformation, metabolite profiles were qualitatively similar following oral or iv administration to rodents and rhesus monkeys. Recainam was extensively metabolized in all species except humans. In human subjects, 84% of the urinary radioactivity corresponded to parent drug. The major metabolites in mouse and rat urine and rat feces were m- and p-hydroxyrecainam. Desisopropylrecainam and dimethylphenylaminocarboxylamino propionic acid were the predominant metabolites in dog and rhesus monkey urine. Small amounts of desisopropylrecainam and p-hydroxyrecainam were excreted in human urine. Selective enzymatic hydrolysis revealed that the hydroxylated metabolites were conjugated to varying degrees among species. Conjugated metabolites were not present in rat urine or feces, while conjugates were detected in mouse, dog, and monkey urine. Structural confirmation of the dog urinary metabolites was accomplished by mass spectral analysis. The low extent of metabolism of recainam in humans suggests that there will not be wide variations between dose and plasma concentrations.     

Species differences in the elimination of a peroxisome proliferator-activated receptor agonist highlighted by oxidative metabolism of its acyl glucuronide.

A species difference was observed in the excretion pathway of 2-[[5,7-dipropyl-3-(trifluoromethyl)-1,2-benzisoxazol-6-yl]oxy]-2-methylpropanoic acid (MRL-C), an alpha-weighted dual peroxisome proliferator-activated receptor alpha/gamma agonist. After intravenous or oral administration of [14C]MRL-C to rats and dogs, radioactivity was excreted mainly into the bile as the acyl glucuronide metabolite of the parent compound. In contrast, when [14C]MRL-C was administered to monkeys, radioactivity was excreted into both the bile and the urine as the acyl glucuronide metabolite, together with several oxidative metabolites and their ether or acyl glucuronides. Incubations in hepatocytes from rats, dogs, monkeys, and humans showed the formation of the acyl glucuronide of the parent compound as the major metabolite in all species. The acyl glucuronide and several hydroxylated products, some which were glucuronidated at the carboxylic acid moiety, were observed in incubations of MRL-C with NADPH- and uridine 5'-diphosphoglucuronic acid-fortified liver microsomes. However, metabolism was more extensive in the monkey microsomes than in those from the other species. When the acyl glucuronide metabolite of MRL-C was incubated with NADPH-fortified liver microsomes, in the presence of saccharo-1,4-lactone, it underwent extensive oxidative metabolism in the monkey but considerably less in the rat, dog, and human liver microsomes. Collectively, these data suggested that the oxidative metabolism of the acyl glucuronide might have contributed to the observed in vivo species differences in the metabolism and excretion of MRL-C.     

Biotransformation of nevirapine, a non-nucleoside HIV-1 reverse transcriptase inhibitor, in mice, rats, rabbits, dogs, monkeys, and chimpanzees.

The study objectives were to characterize the metabolism of nevirapine (NVP) in mouse, rat, rabbit, dog, monkey, and chimpanzee after oral administration of carbon-14-labeled or -unlabeled NVP. Liquid scintillation counting quantitated radioactivity and bile, plasma, urine, and feces were profiled by HPLC/UV diode array and radioactivity detection. Metabolite structures were confirmed by UV spectral and chromatographic retention time comparisons with synthetic metabolite standards, by beta-glucuronidase incubations, and in one case, by direct probe electron impact ionization/mass spectroscopy, chemical ionization/mass spectroscopy, and NMR. NVP was completely absorbed in both sexes of all species except male and female dogs. Parent compound accounted for <6% of total urinary radioactivity and <5.1% of total fecal radioactivity, except in dogs where 41 to 46% of the radioactivity was excreted as parent compound. The drug was extensively metabolized in both sexes of all animal species studied. Oxidation to hydroxylated metabolites occurred before glucuronide conjugation and excretion in urine and feces. Hydroxylated metabolites were 2-, 3-, 8-, and 12-hydroxynevirapine (2-, 3-, 8-, and 12-OHNVP). 4-carboxynevirapine, formed by secondary oxidation of 12-OHNVP, was a major urinary metabolite in all species except the female rat. Glucuronides of the hydroxylated metabolites were major or minor metabolites, depending on the species. Rat plasma profiles differed from urinary profiles with NVP and 12-OHNVP accounting for the majority of the total radioactivity. Dog plasma profiles, however, were similar to the urinary profiles with 12-OHNVP, its glucuronide conjugate, 4-carboxynevirapine, and 3-OHNVP glucuronide being the major metabolites. Overall, the same metabolites are formed in animals as are formed in humans.     

Absorption, metabolism, and excretion of [(14)C]MK-0524, a prostaglandin D(2) receptor antagonist, in humans.

[(3R)-4-(4-Chlorobenzyl)-7-fluoro-5-(methylsulfonyl)-1,2,3,4-tetrahydrocyclopentaindol-3-yl]acetic acid (MK-0524) is a potent orally active human prostaglandin D(2) receptor 1 antagonist that is currently under development for the prevention of niacin-induced flushing. The metabolism and excretion of [(14)C]MK-0524 in humans were investigated in six healthy human volunteers following a single p.o. dose of 40 mg (202 microCi). [(14)C]MK-0524 was absorbed rapidly, with plasma C(max) achieved 1 to 1.5 h postdose. The major route of excretion of radioactivity was via the feces, with 68% of the administered dose recovered in feces. Urinary excretion averaged 22% of the administered dose, for a total excretion recovery of approximately 90%. The majority of the dose was excreted within 96 h following dosing. Parent compound was the primary radioactive component circulating in plasma, comprising 42 to 72% of the total radioactivity in plasma for up to 12 h. The only other radioactive component detected in plasma was M2, the acyl glucuronic acid conjugate of the parent compound. The major radioactive component in urine was M2, representing 64% of the total radioactivity. Minor metabolites included hydroxylated epimers (M1/M4) and their glucuronic acid conjugates, which occurred in the urine as urea adducts, formed presumably during storage of samples. Fecal radioactivity profiles mainly comprised the parent compound, originating from unabsorbed parent and/or hydrolyzed glucuronic acid conjugate of the parent compound. Therefore, in humans, MK-0524 was eliminated primarily via metabolism to the acyl glucuronic acid conjugate, followed by excretion of the conjugate into bile and eventually into feces.     

Formation and protein binding of the acyl glucuronide of a leukotriene B4 antagonist (SB-209247): relation to species differences in hepatotoxicity.

SB-209247 [(E)-3-[6-[[(2,6-dichlorophenyl)-thio]methyl]-3-(2-phenylethoxy)-2-pyridinyl]-2-propenoic acid], an anti-inflammatory leukotriene B4 receptor antagonist, was associated in beagle dogs but not male rats with an inflammatory hepatopathy. It also produced a concentration-dependent (10-1000 microM) but equal leakage of enzymes from dog and rat precision-cut liver slices. The hepatic metabolism of SB-209247 was investigated with reference to the formation of reactive acyl glucuronides. [14C]SB-209247 (100 micromol/kg) administered i.v. to anesthetized male rats was eliminated by biliary excretion of the acyl glucuronides of the drug and its sulfoxide. After 5 h, 1.03 +/- 0.14% (mean +/- S.E.M., n = 4) of the dose was bound irreversibly to liver tissue. The sulfoxide glucuronide underwent pH-dependent rearrangement in bile more rapidly than did the SB-209247 conjugate. [14C]SB-209247 was metabolized by sulfoxidation and glucuronidation in rat and dog hepatocytes, and approximately 1 to 2% of [14C]SB-209247 (100 microM) became irreversibly bound to cellular material. [14C]SB-209247 sulfoxide and glucuronide were the only metabolites produced by dog, rat, and human liver microsomes in the presence of NADPH and UDP-glucuronic acid (UDPGA), respectively. V(max) values for [14C]SB-209247 glucuronidation by dog, rat, and human microsomes were 2.6 +/- 0.1, 1.2 +/- 0.1, and 0.4 +/- 0.0 nmol/min/mg protein, respectively. Hepatic microsomes from all three species catalyzed UDPGA-dependent but not NADPH-dependent irreversible binding of [14C]SB-209247 (100-250 microM) to microsomal protein. Although a reactive acyl glucuronide was formed by microsomes from every species, the binding did not differ between species. Therefore, neither the acute cellular injury nor glucuronidation-driven irreversible protein binding in vitro is predictive of the drug-induced hepatopathy.     

Disposition, metabolism and mass balance of [(14)C]apremilast following oral administration

Apremilast is a novel, orally available small molecule that specifically inhibits PDE4 and thus modulates multiple pro- and anti-inflammatory mediators, and is currently under clinical development for the treatment of psoriasis and psoriatic arthritis. The pharmacokinetics and disposition of [(14)C]apremilast was investigated following a single oral dose (20?mg, 100 μCi) to healthy male subjects. Approximately 58% of the radioactive dose was excreted in urine, while faeces contained 39%. Mean C(max), AUC(0-∞) and t(max) values for apremilast in plasma were 333?ng/mL, 1970 ng*h/mL and 1.5?h. Apremilast was extensively metabolized via multiple pathways, with unchanged drug representing 45% of the circulating radioactivity and <7% of the excreted radioactivity. The predominant metabolite was O-desmethyl apremilast glucuronide, representing 39% of plasma radioactivity and 34% of excreted radioactivity. The only other radioactive components that represented >4% of the excreted radioactivity were O-demethylated apremilast and its hydrolysis product. Additional minor circulating and excreted compounds were formed via O-demethylation, O-deethylation, N-deacetylation, hydroxylation, glucuronidation and/or hydrolysis. The major metabolites were at least 50-fold less pharmacologically active than apremilast. Metabolic clearance of apremilast was the major route of elimination, while non-enzymatic hydrolysis and excretion of unchanged drug were involved to a lesser extent.     

Pharmacokinetics and pharmacodynamics of the vasopeptidase inhibitor,omapatrilat in healthy subjects

AIMS: To determine the pharmacokinetics, pharmacodynamics and tolerability of omapatrilat, a vasopeptidase inhibitor, in healthy subjects. METHODS: The effects of oral omapatrilat were evaluated in healthy men in two double-blind, placebo-controlled, dose-escalation trials. In a single-dose study, subjects received omapatrilat in doses of 2.5, 7.5, 25, 50, 125, 250, or 500 mg. In a multiple-dose study, subjects received doses of 10, 25, 50, 75, or 125 mg daily for 10 days. RESULTS: In the multiple-dose study, peak plasma concentrations (Cmax = 10-895 ng ml(-1); tmax = 0.5-2 h) of omapatrilat were attained rapidly. Omapatrilat exhibited a long effective half-life (14-19 h), attaining steady state in 3-4 days. In the single-dose study, Cmax (1-1009 ng ml(-1)) and AUC(0,t) (0.4-1891 ng ml(-1) h) were linear but not dose proportional. In the multiple-dose study, based on weighted least-squares linear regression analyses vs dose, Cmax but not AUC(0,t) was linear at the lower doses on day 10. The lowest dose of omapatrilat (2.5 mg) almost completely inhibited (> 97%) serum angiotensin converting enzyme activity at 2 h after dosing. In the multiple dose study, angiotensin converting enzyme activity was inhibited by more than 80% 24 h after all doses of omapatrilat. Inhibition of neutral endopeptidase activity was shown by increases in the daily urinary excretion of atrial natriuretic peptide and cyclic guanosine monophosphate at doses of more than 7.5 and 25 mg, respectively. In the single dose study, omapatrilat increased the daily urinary excretion of atrial natriuretic peptide dose-dependently from 10.8 +/- 4.1 (+/- SD) ng 24 h(-1) in the placebo group to 60.0 +/- 18.2 ng 24 h(-1) in the 500 mg group. Omapatrilat did not affect sodium and potassium excretion or urinary volume. Compared with placebo, omapatrilat produced a decrease in mean arterial pressure at 3 h after all doses in both the single- and multiple-dose studies. CONCLUSIONS: Omapatrilat was generally well tolerated. The pharmacokinetic and pharmacodynamic effects of omapatrilat are consistent with once-daily dosing.     

Metabolism and disposition of GTS-21, a novel drug for Alzheimer's disease.

1. GTS-21, a novel drug for Alzheimer's disease, is currently under clinical development. In the current study, the metabolism and disposition of GTS-21 have been evaluated in rat and dog after single oral and intravenous administration. 2. Following oral administration of [14C]GTS-21 to rat, radioactivity was primarily excreted in the faeces (67%) via the bile with possible enterohepatic circulation. Urinary excretion of radioactivity in rat and dog was 20 and 19% respectively. 3. GTS-21 was rapidly and extensively absorbed after oral administration and rapidly cleared from plasma. The maximum concentration ratio of GTS-21 to total radioactivity in plasma was low, indicating first-pass or pre-systemic biotransformation. 4. In rat, GTS-21 showed linear pharmacokinetics over doses ranging from 1 to 10 mg/kg with an absolute bioavailability of 23%. In dog, the absolute bioavailability was 27% at an oral dose of 3 mg/kg. 5. GTS-21 was O-demethylated to yield compounds that were then subject to glucuronidation. Three of the metabolites in rat urine were isolated and characterized as 4-OH-GTS-21, 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. The major urinary metabolites were 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. 6. In vitro chemical inhibition of cytochrome P450 in human liver microsomes indicated that CYPIA2 and CYP2E1 were the isoforms primarily responsible for the O-demethylation of GTS-21, with some contribution from CYP3A.     

The metabolic disposition of aprepitant, a substance P receptor antagonist, in rats and dogs.

The absorption, metabolism, and excretion of [14C]aprepitant, a potent and selective human substance P receptor antagonist for the treatment of chemotherapy-induced nausea and vomiting, was evaluated in rats and dogs. Aprepitant was metabolized extensively and no parent drug was detected in the urine of either species. The elimination of drug-related radioactivity, after i.v. or p.o. administration of [14C]aprepitant, was mainly via biliary excretion in rats and by way of both biliary and urinary excretion in dogs. Aprepitant was the major component in the plasma at the early time points (up to 8 h), and plasma metabolite profiles of aprepitant were qualitatively similar in rats and dogs. Several oxidative metabolites of aprepitant, derived from N-dealkylation, oxidation, and opening of the morpholine ring, were detected in the plasma. Glucuronidation represented an important pathway in the metabolism and excretion of aprepitant in rats and dogs. An acid-labile glucuronide of [14C]aprepitant accounted for approximately 18% of the oral dose in rat bile. The instability of this glucuronide, coupled with its presence in bile but absence in feces, suggested the potential for enterohepatic circulation of aprepitant via this conjugate. In dogs, the glucuronide of [14C]aprepitant, together with four glucuronides derived from phase I metabolites, were present as major metabolites in the bile, accounting collectively for approximately 14% of the radioactive dose over a 4- to 24-h period after i.v. dosing. Two very polar carboxylic acids, namely, 4-fluoro-alpha-hydroxybenzeneacetic acid and 4-fluoro-alpha-oxobenzeneacetic acid, were the predominant drug-related entities in rat and dog urine.     

Metabolism of (14C)-quazodine in the rat, dog, and man.

The pharmacokinetics of [¹⁴C]-quazodine, a new bronchodilator, were examined in man and dog. Absorption, metabolism, and excretion of quazodine were studied in the rat, dog, and man, while distribution of the drug was measured in rats. After iv dosage, clearance of unchanged drug from plasma was rapid in both dogs and man and followed a biexponential decay curve in accordance with the equation C_p = Ae^?αt + Be^?βt. A good fit between the actual data and the computer-generated curves was obtained employing a nonlinear regression analysis computer program. After po administration quazodine was rapidly absorbed in both man and dog, a peak plasma concentration being observed at 0.5 hr in man and at 1 hr in dogs. The drug did not localize in cerebrospinal fluid of dogs. Radioactivity was found in all tissues of rats at 1 hr after oral dosage, and no evidence for extreme drug localization or prolonged retention was found in any tissue including brain. In rats, 71.9% of the dose was recovered in urine and 14.2% in feces during the first 3 days after dosing. The 72-hr recoveries in dog urine and feces were 61.4 and 25.8%, whereas in humans these values were 84.1 and 1.1%, respectively. The major pathway for metabolism of quazodine in man, and to a lesser extent in the dog and rat, was by demethylation at the 7-position of the quinazoline ring-system followed by conjugation with glucuronic acid or sulfate. The glucuronide conjugate accounted for 78.0% of the radioactivity in human urine, 45.1% in dog, and 27.4% in rat urine. The amount of radioactivity present as the sulfate conjugate was 3.1, 15.3, and 10.5% in human, dog, and rat urine, respectively.     

The Metabolic Fate of the Coronary Dilator 4-(3,4,5-Trimethoxycinnamoyl)-1-(N-Isopropylcarbamoylmethyl)- Piperazine in the Rat,Dog and Man

1. An oral dose of the coronary dilator 4-(3,4,5-trimethoxycinnamoyl)-1- (N-isopropylcarbamoylmethyl)-piperazine was readily absorbed and more than 75% of the dose was excreted within 24 h by the rat, dog and man. In 4 days, rat, dog and man excreted in the urine and faeces respectively 32.5 and 62.3%, 43.9 and 49.1%, and 57.8 and 43.3%. Faecal radioactivity was mainly excreted via the bile.

2. Plasma concentrations of radioactivity reached a maximum within 1 h in rats and dogs and within 2 h in man. For several h, more than 50% of the radioactivity circulating in the plasma of rats and more than 80% in man was due to unchanged drug.

3. Sequential whole-body autoradiography of the rat indicated that much of the radioactivity was distributed in the liver, kidneys and gastrointestinal tract and that there was significant uptake into the heart and lungs.

4. Although similar metabolites were excreted by the rat, dog and man, the relative proportions differed. 11.7, 2.3 and 28.8% respectively of the unchanged drug were excreted in the urine and 13.1, 19.5 and 10.4% respectively of the principal metabolite a glucuronide whose exact structure was not determined. Other metabolites included 4-(3,4,5-trimethoxycinnamoyl)-1-carbamoylmethyl piperazine and N-(3,4,5-trimethoxycinnamoyl)-piperazine.     

Metabolism of methylphenidate in dog and rat

The urinary metabolites of methylphenidate in the dog and rat were investigated. After oral administration of 14C-labeled methylphenidate, approximately 86% and 63% of the dose was recovered in the urine of the dog and rat, respectively. Less than 1% of the dose was excreted as unchanged drug. Metabolism involved oxidation, hydrolysis, and conjugation processes. The primary hydrolytic product was alpha-phenyl-2-piperidineacetic acid (24%, dog; 35-40%, rat). The primary metabolites of oxidation were methyl 6-oxo-alpha-phenyl-2-piperidineacetate (3%, dog; 1.5%, rat) and the glucuronide of alpha-(p-hydroxyphenyl)-2-piperidineacetic acid (10%, rat). The former also underwent extensive biotransformation, including: 1) hydrolysis to the lactam acid (27%, dog; 7-10%, rat) and subsequent carboxylic acid O-glucuronidation (15%, dog); or 2) hydroxylation at the 5-position (1%, dog; 2%, rat) and subsequent hydrolysis (4%, dog; 15-17%, rat); or 3) 5-O-glucuronidation (12%, dog). Additional minor metabolites from methyl-6-oxo-alpha-phenyl-2-piperidineacetate were the phenolic O-glucuronide of methyl alpha-(p-hydroxyphenyl)-6-oxo-2-piperidineacetate (1%, dog), and the 4-O-glucuronide of methyl 4-hydroxy-6-oxo-alpha-phenyl-2-piperidineacetate (1%, dog), and the taurine amide conjugate of alpha-(p-hydroxyphenyl)-6-oxo-2-piperidineacetic acid (1%, dog). Additional products from methylphenidate conjugation included methyl 1-carbamoyl-alpha-phenyl-2-piperidineacetate (1%, dog or rat) and its carboxylic acid hydrolysis product (1%, rat). The chirality of the major metabolites isolated from dog urine showed that metabolism was partially stereoselective in all investigated cases, except in the formation of alpha-phenyl-2-piperidineacetic acid.     

Metabolism of [2-14C]p-hydroxyphenyl acetic acid in rat, monkey and human hepatocytes and in bile-duct cannulated rats

We determined the metabolism of [2-(14)C]p-hydroxyphenyl acetic acid (p-HPA) in rat (male, Sprague-Dawley), monkey (male, Cynomolgus), and human (male, Caucasian) hepatocytes, and in bile-duct cannulated (BDC) rats (male, Sprague-Dawley). Unchanged p-HPA ranged from 87.0 to 92.6% of the total radioactivity (TRA) in the extracts of rat, monkey, and human hepatocytes. Metabolites M1 (a glucuronide conjugate of p-HPA) and M2 (a glycine conjugate of p-HPA) were detected, accounting for 1-4% of TRA. After an oral dose of [2-(14)C]p-HPA to BDC rats, p-HPA-related components was predominantly excreted in urine, accounting for 83% of the dose. Bile excretion was limited, accounting for only 1.5% of the dose. Unchanged p-HPA was the predominant radioactivity in plasma (84.6% of the TRA in 1-h pooled plasma) and urine (69.6% of the dose). Metabolites M1, M2, and M3 (a glucuronide of p-HPA) were all detected in plasma, urine, and bile as minor components. In summary, p-HPA was not metabolized extensively in rat, monkey, and human hepatocytes. In rats, absorption and elimination of p-HPA were nearly complete with urinary excretion of the unchanged p-HPA as the predominant route of elimination after oral dosing. No oxidative metabolites were detected, suggesting a minimal role for P450 enzymes in its overall metabolic clearance. Therefore, p-HPA has a low potential for drug-drug interactions mediated by the concomitant inhibitors and inducers of P450 enzymes.     

Metabolism of loprazolam in rat, dog and man in vivo

The metabolism of 14C-loprazolam has been studied in rat, dog and man in vivo. In rat, the major metabolic pathways were hydroxylation on the benzodiazepine ring, and reduction and acetylation of the nitro group. Both metabolites were identified by co-chromatography with standards, and were present in urine and bile conjugated with glucuronic acid. In both dog and human urine and bile significant amounts of the piperazine-N-oxide were found. This N-oxide was identified by co-chromatography with authentic compound and by mass spectroscopy. Both loprazolam and the dog biliary metabolites were hydrolysed spontaneously to polar material. Neither treatment with beta-glucuronidase nor incubation with gut microflora had any further effect. Only polar metabolites were found in dog and human faeces. The principal non-polar material found in rat plasma was the diazepine-hydroxy compound, and little loprazolam was present. Significant levels of loprazolam and lower levels of an unidentified metabolite were found in ether extracts of dog and human plasma. Both the piperazine-N-oxide and loprazolam were found in similar quantities in chloroform extracts of human plasma, and at two hours after dosage, the N-oxide and loprazolam accounted for greater than 90% of the radioactivity present in the plasma.