Metabolism and excretion of a new antianxiety drug candidate, CP-93,393, in cynomolgus monkeys: identification of the novel pyrimidine ring cleaved metabolites

The metabolism and excretion of a new anxiolytic/antidepressant drug candidate, CP-93,393, ((7S, 9aS)-1-(2-pyrimidin-2-yl-octahydro-pyrido[1, 2-a]-pyrazin-7-yl-methyl)-pyrrolidine-2,5-dione) were investigated in cynomolgus monkeys after oral administration of a single 5 mg/kg dose of 14C-CP-93,393. Urine, bile, feces, and blood samples were collected and assayed for total radioactivity, parent drug, and metabolites. Total recovery of the administered dose after 6 days was 80% with the majority recovered during the first 48 hr. An average of 69% of the total radioactivity was recovered in urine, 4% in bile, and 7% in feces. Mean Cmax and AUC(0-infinity) values for the unchanged CP-93,393 were 143.2 ng/ml and 497.7 ng.hr/ml, respectively, in the male monkeys and 17.2 ng/ml and 13.7 ng.hr/ml, respectively, in the female monkeys. HPLC analysis of urine, bile, feces, and plasma from both male and female monkeys indicated extensive metabolism of CP-93,393 to several metabolites. The identification of metabolites was achieved by chemical derivatization, beta-glucuronidase/sulfatase treatment, and by LC/MS/MS, and the quantity of each metabolite was determined by radioactivity detector. CP-93,393 undergoes metabolism by three primary pathways, aromatic hydroxylation, oxidative degradation of the pyrimidine ring, and hydrolysis of the succinimide ring followed by a variety of secondary pathways, such as oxidation, methylation, and conjugation with glucuronic acid and sulfuric acid. The major metabolites, oxidation on the pyrimidine ring to form 5-OH-CP-93,393 (M15) followed by glucuronide and sulfate conjugation (M7 and M13), accounted for 35-45% of the dose in excreta. Two metabolites (M25 and M26) were formed by further oxidation of M15 followed by methylation of the resulting catechol intermediate presumably by catechol-O-methyl transferase. A novel metabolic pathway, resulting in the cleavage of the pyrimidine ring, was also identified. The metabolites (M18, M20, and M21) observed from this pathway accounted for 8-15% of the dose. Aliphatic hydroxylation of the succinimide ring was a very minor pathway in monkey. 5-Hydroxy-CP-93,393 (M15, 37-49%), its sulfate and glucuronide conjugates (M7 and M13, approximately 34%), and the pyrimidine ring cleaved product (M18, approximately 8%) were the major metabolites in monkey plasma. The identified metabolites accounted for approximately 90, 93, 97, and 92% of the total radioactivity present in urine, bile, plasma, and feces, respectively. The major in vivo oxidative metabolites were also observed after in vitro incubations with monkey liver microsomes.     

Psychosocial aspects of palliative care

The metabolites of [2,3-14C]acrolein in the urine and feces of Sprague-Dawley rats were identified after either intravenous administration in saline at 2.5 mg/kg or oral administration by gavage as an aqueous solution as either single or multiple doses at 2.5 mg/kg or as a single dose of 15 mg/kg. Selected urine and feces samples were pooled by sex and collection interval and profiled by combinations of reverse-phase, anion-exchange, cation-exchange, and ion-exclusion high-performance liquid chromatography (HPLC). Feces were also profiled by size-exclusion chromatography. Metabolites were identified by comparison with well-characterized standards by HPLC and by mass spectrometry. The urinary metabolites were identified as oxalic acid, malonic acid, N-acetyl-S-2-carboxy-2-hydroxyethylcysteine, N-acetyl-S-3-hydroxypropylcysteine, N-acetyl-S-2-carboxyethylcysteine, and 3-hydroxypropionic acid. The fecal radioactivity from the oral dose groups was partitioned into methanol-soluble, water-soluble, and insoluble radioactivity, some of which could be liberated by dilute acid hydrolysis. HPLC analysis of these extracts revealed no discrete metabolites. Size-exclusion chromatography indicated a molecular weight range of 2,000 to 20,000 Da for the radioactivity, which was unaffected by hydrolysis at reflux with 6 M acid or base. This radio-activity was thought to be a homopolymer of acrolein, which was apparently formed in the gastrointestinal tract. The pathways of acrolein metabolism were epoxidation followed by conjugation with glutathione, Michael addition of water followed by oxidative degradation, and glutathione addition to the double bond either following or preceding oxidation or reduction of the aldehyde. The glutathione adducts were further metabolized to the mercapturic acids.     

Bioavailability, multiple-dose pharmacokinetics, and biotransformation of the aldose reductase inhibitor zopolrestat in dogs

Zopolrestat (Alond) is a new drug that is being evaluated as an aldose reductase inhibitor for the treatment of diabetic complications. The bioavailability in dogs of a 2 mg/kg oral dose of zopolrestat was 97.2%. In a 1-year, multiple-dose, pharmacokinetic study, systemic exposure increased with increasing dose (50, 100, and 200 mg/kg/day), and there were no consistent changes in exposure with multiple dosing. Renal clearance at 1 year appeared to be higher in males. The magnitude of the potential gender difference in exposure was relatively small and was unlikely to have had a meaningful impact on the pharmacokinetics of zopolrestat in dogs. In studies with bile duct-cannulated dogs, radioactivity from [14C]zopolrestat was primarily eliminated as unchanged drug and acyl glucuronide in the bile and feces (77.3% of the dose) and in urine (18.3% of the dose). The concentrations of acyl glucuronide in urine and feces were approximately 50% of the zopolrestat concentrations. Minor metabolites (each accounting for <1% of the dose) included those resulting from hydroxylation of the phthalazinone ring and glutathione conjugation of the benzothiazole ring.     

Pharmacokinetics of single intravenous and oral doses of dolasetron mesylate in healthy elderly volunteers

Dolasetron mesylate (MDL 73,147EF, Anzemet; Hoechst Marion Roussel, Laval, Canada) is a 5-HT3 receptor antagonist undergoing clinical evaluation for use as an antiemetic agent. The pharmacokinetics of dolasetron and its reduced metabolite (MDL 74,156) were studied after administration of single intravenous and oral doses of dolasetron mesylate 2.4 mg/kg in 18 healthy elderly subjects. Expressed as the dolasetron base, this dose was 1.8 mg/kg. Dolasetron was rapidly metabolized to the reduced metabolite, which appeared in plasma within 10 minutes after intravenous or oral administration. The mean half-life (t1/2) of dolasetron was 0.24 hours after intravenous administration and 0.50 hours after oral administration. The pharmacokinetic parameters of the reduced metabolite were similar after intravenous and oral administration. The apparent absolute bioavailability of the reduced metabolite was 89%, and it had an elimination t1/2 of approximately 7 hours and an apparent volume of distribution (Vd beta) of 4.69 L/kg. Dolasetron was not detected in urine. Metabolites were excreted in urine almost completely within 24 hours of administration. The primary metabolite detected in urine was the (+)-enantiomer of the reduced metabolite, which accounted for 25.35% (+/- 7.79%) and 18.88% (+/- 7.65%) of the intravenous and oral doses, respectively. Hydroxylated metabolites accounted for 5% or less of the total dose via either route. The pharmacokinetics of the reduced metabolite after single intravenous or oral doses in elderly volunteers were consistent with pharmacokinetics observed in both young healthy men and cancer patients receiving high-dose cisplatin chemotherapy. Dosage adjustments of dolasetron mesylate on the basis of age do not appear to be necessary.     

The metabolism of the hypolipidaemic drug sultosilic acid in rat, dog and man

1. Single oral doses of the hypolipidaemic drug [35S]sultosilic acid to rats (40 mg/kg), dogs (40 mg/kg) and man (7 mg/kg) were well absorbed. During three days, means of 59.2%, 58.8% and 61.8% in urine and 37.7%, 31.9% and 19.7% in faeces, were excreted by these species respectively. Most of the dose was excreted during the first 24 h. 2. Peak plasma levels of 35S were generally reached during 1-2 h after oral doses in rats (12 micrograms equiv./ml), dogs (45 micrograms equiv./ml) and two human subjects (15.2 and 10.3 micrograms equiv./ml). In humans, peak plasma levels of unchanged drug (at 1-1.5 h) were 10.5 and 6.3 micrograms/ml. Plasma concentrations of 35S increased almost proportionately to dose in rats following oral doses of 400 and 1200 mg/kg, although in dogs, concentrations were similar at these two dose levels but several times higher than at 40 mg/kg. 3. Tissue concn. of 35S were generally higher in rats than in dogs. Highest concn. occurred at 3 h in rats and 1 h in dogs. Apart from those in the liver and kidneys, tissue concn. were appreciably lower than the corresponding plasma levels. 4. The major radioactive component in dog urine was sultosilic acid. Rat and human urine contained sultosilic acid and also two more polar major metabolites. In male and female rat urine, the proportions of these excretory products differed and the proportions in male rat urine were similar to those in human urine. Sultosilic acid was also the only component detected in dog plasma, whereas rat and human plasma also contained the two urine metabolites. Dog bile contained a conjugate of sultosilic acid. 5. The two metabolites have been identified by mass spectrometry and nuclear magnetic resonance spectroscopy as products resulting from oxidation of the methyl in the p-toluenesulphonyl group. The structures assigned are the corresponding carboxylic acid and the hydroxymethyl derivatives.     

Depressive disorders in mentally retarded children. A review of selected literature. Part II

1. The metabolism of 1-(2-methoxyphenyl)-2-methyl-2-(3-pyridyl)-1-propanone (2-MPMP) was studied in the male Sprague-Dawley rat after 50 mg/kg, i.v. dose. 2. Organic solvent extracts of urine samples were directly analysed by reversed-phase gradient hplc. The identified metabolites were also isolated by preparative tlc, and analyzed by direct probe mass spectrometry. In the case of conjugated metabolites, the urine samples were deconjugated by enzyme hydrolysis prior to extraction. The structures of metabolites were confirmed by comparison of their chromatographic behaviours, UV spectra, and mass spectra with those of authentic standards. 3. The metabolites identified in the 0-24-h urine samples were 2-hydroxyphenyl-metyrapone (2-OHPMP) and 2-hydroyphenylmetyrapone N-oxide (2-OHPMP-NO), which were present predominantly as their glucuronide and/or sulphate conjugates. 4. 2-MPMP and four of its metabolites present in the 0-24-h urine samples were quantified by a reversed-phase hplc method. The mean total urinary excretion was 75.4% of the administered dose. The major metabolites present in the urine were conjugates of 2-OHPMP-NO (54.4%) and of 2-OHPMP (18.6%). The excretion of the unchanged drug, unconjugated 2-OHPMP and 2-OHPMP-NO accounted for 1.1, 1.1 and 0.2% of the dose respectively.     

Isolation and identification of major urinary metabolites of rifabutin in rats and humans

The antimycobacterial drug rifabutin is extensively metabolized in humans and laboratory animals. About 40% of the dose is excreted in urine as unchanged drug, and lipophilic (extractable with 1-chlorobutane) and polar metabolites. Polar metabolites accounted for 59.1 +/- 2.5% and 88.8 +/- 4.4% of radioactivity in urine collected over 96 hr after intravenous administration of 25 and 1 mg/kg of [14C]rifabutin to Sprague-Dawley rats, respectively. After 48 hr, all urinary radioactivity consisted of polar metabolites. The most abundant polar metabolite, identified by electrospray ionization-MS, collision-induced dissociation-MS, and comparison of HPLC retention times with the synthetic standard, was N-isobutyl-4-hydroxy-piperidine. Lipophilic metabolites accounted for <20% of urinary radioactivity. Major lipophilic metabolites, 25-O-deacetyl-rifabutin, 27-O-demethyl-rifabutin, 31-hydroxy-rifabutin, 32-hydroxy-rifabutin, and 20-hydroxy-rifabutin were isolated from both human and rat urine by HPLC and identified by electrospray ionization-MS, collision-induced dissociation-MS, and NMR spectrometry. In addition, two metabolites formed by the oxidation of the N-isobutyl-piperidyl group of rifabutin were found in the urine of rats, but not humans.     

In vivo disposition and metabolism by liver and enterocyte microsomes of the antitubercular drug rifabutin in rats

The in vivo disposition and in vitro metabolism of rifabutin, a new spiropiperidylrifamycin, were studied in rats and in microsomes from rat liver and enterocytes, respectively. After i.v. doses of 1,5, 10 and 25 mg/kg the systemic clearance was 0.7 to 1.0 liters/hr/kg; the volume of distribution was 4.4 liters/kg for the 1 mg/kg dose and 7.4 to 7.7 liters/kg for the 5 to 25 mg/kg doses, and the half-life ranged from 4.4 to 9.1 hr. Urinary and fecal excretion over 0 to 96 hr after i.v. administration of 25 mg/kg [14C]rifabutin accounted for 40.1 and 52.2% of the dose, respectively. Exteriorization of the bile duct showed that approximately 24% of the dose was eliminated in bile, > or = 98% as metabolites. Bioavailability after oral administration of 25 and 1 mg/kg rifabutin was > 90% and 44%, respectively, suggesting significant first-pass metabolism of the lower dose. Concentrations of rifabutin in gastric juice were 10 to 17 times higher than in blood, indicating extensive secretion into the stomach. Experiments with the isolated small intestinal loop demonstrated direct exsorption of the drug into the lumen. The rate of rifabutin metabolism by enterocyte microsomes was > 10 times higher than that by liver microsomes, i.e., 84 and 8 pmol/min/mg protein, respectively. Biotransformation of rifabutin in vivo and in vitro was markedly induced by dexamethasone and inhibited by erythromycin, suggesting that CYP3A is involved in the metabolism of rifabutin. Several metabolites, including 20-OH-rifabutin and 27-O-demethyl-rifabutin, isolated from urine and microsomes were identified by mass spectrometry and nuclear magnetic resonance spectroscopy.     

Pharmacokinetics and metabolism in mice of a phosphorothioate oligonucleotide antisense inhibitor of C-raf-1 kinase expression

The plasma and tissue disposition of CGP 69846A (ISIS 5132) was characterized in male CD-1 mice following iv bolus injections administered every other day for 28 days (total of 15 doses). The doses ranged from 0.8 mg/kg to 100 mg/kg. Urinary excretion of oligonucleotide was also monitored over a 24-hr period following single dose administration over the same dose range. Pharmacokinetic plasma profiles were determined following single dose administration (dose 1) and after multiple doses (dose 15) at doses of 4 and 20 mg/kg. Concentrations in kidney, liver, spleen, heart, lung, and lymph nodes were characterized following doses 1, 8, and 15 for all doses. Capillary gel electrophoresis was used to quantitate intact (full-length) oligonucleotide and its metabolites (down to N - 11 base deletions) in both plasma and tissue at all time points. The plasma and tissue disposition of CGP 69846A was characterized by a rapid distribution into all tissues analyzed. Rapid plasma clearance of the parent oligonucleotide (9.3-14.3 ml/min/kg) was predominantly the result of distribution to tissue and, to a lesser extent, metabolism. Appearance and pattern of chain-shortened metabolites seen in plasma and tissue were consistent with predominantly exonuclease-mediated base deletion. No measurable accumulation of oligonucleotide was observed in plasma following multiple-dose administration, but both the liver and the kidney exhibited 2-3-fold accumulations. In general, the tissues exhibited half-lives for the elimination of parent oligonucleotide of 16-60 hr compared with plasma half-lives of 30-45 min. After repeated administrations, significant decreases in plasma clearance and volume of distribution at steady state (Vss) were observed following dose 15 at the dose of 20 mg/kg but not at the dose of 4 mg/kg. Changes in tissue accumulation and evidence for saturation of tissue distribution at the high doses may explain the plasma disposition changes observed in the absence of alteration of metabolism or plasma accumulation. Urinary excretion was a minor pathway for elimination of oligonucleotide over the 24-hr period immediately following iv administration. However, the amount of oligonucleotide excreted in the urine increased as a function of dose from less than 1% to approximately 13% of the administered dose over a dose range of 0.8 mg/kg to 100 mg/kg.     

Biotransformation of irbesartan in man

The metabolism of irbesartan, a highly selective and potent nonpeptide angiotensin II receptor antagonist, has been investigated in humans. An aliquot of pooled urine from healthy subjects given a 50-mg oral dose of [14C]irbesartan was added as a tracer to urine from healthy subjects that received multiple, 900-mg nonradiolabeled doses of irbesartan. Urinary metabolites were isolated, and structures were elucidated by mass spectroscopy, proton NMR, and high-performance liquid chromatography (HPLC) retention times. Irbesartan and the following eight metabolites were identified in human urine: (1) a tetrazole N2-beta-glucuronide conjugate of irbesartan, (2) a monohydroxylated metabolite resulting from omega-1 oxidation of the butyl side chain, (3, 4) two different monohydroxylated metabolites resulting from oxidation of the spirocyclopentane ring, (5) a diol resulting from omega-1 oxidation of the butyl side chain and oxidation of the spirocyclopentane ring, (6) a keto metabolite resulting from further oxidation of the omega-1 monohydroxy metabolite, (7) a keto-alcohol resulting from further oxidation of the omega-1 hydroxyl of the diol, and (8) a carboxylic acid metabolite resulting from oxidation of the terminal methyl group of the butyl side chain. Biotransformation profiles of pooled urine, feces, and plasma samples from healthy male volunteers given doses of [14C]irbesartan were determined by HPLC. The predominant drug-related component in plasma was irbesartan (76-88% of the plasma radioactivity). None of the metabolites exceeded 9% of the plasma radioactivity. Radioactivity in urine accounted for about 20% of the radiolabeled dose. In urine, irbesartan and its glucuronide each accounted for about 5 to 10% of the urinary radioactivity. The predominant metabolite in urine was the omega-1 hydroxylated metabolite, which constituted about 25% of the urinary radioactivity. In feces, irbesartan was the predominant drug-related component (about 30% of the radioactivity), and the primary metabolites were monohydroxylated metabolites and the carboxylic acid metabolite. Irbesartan and these identified metabolites constituted 90% of the recovered urinary and fecal radioactivity from human subjects given oral doses of [14C]irbesartan.     

Metabolism of 4-methylaminorex ("EU4EA") in the rat

Metabolism studies were conducted on 4-methylaminorex (4,5-dihydro-4-methyl-5-phenyl-2-oxazolamine [4-MAX]), a potent central nervous system stimulant that has emerged as a drug of abuse under the name "EU4EA", "EU4Euh", and "Ice". Tritiated norephedrine was cyclized with cyanogen bromide to form 3H-4-MAX, which was administered to rats at a dose of 10 mg/kg orally and intravenously. Radioactivity was excreted almost entirely in urine (40% of the dose was excreted by 24 h), primarily as the parent drug (60% of the total excretions were as the parent compound). Three metabolites were identified by high-performance liquid chromatography-tandem mass spectrometry with thermospray ionization: norephedrine, 5-phenyl-4-methyl-2-oxazolidinone, and 2-amino-5-(p-hydroxyphenyl)-4-methyl-2-oxazoline. Stability studies showed that 4-MAX in aqueous solution degraded very slightly to norephedrine upon standing. There was no evidence for glucuronide or sulfate conjugation. These results suggest that the metabolic fate of 4-MAX is similar to that of the amphetamines in that it is eliminated primarily unchanged but undergoes some slight oxidative deamination and aromatic hydroxylation. Hydrolytic degradation back to the synthetic precursor can also occur. There was no evidence for the hydrolysis of the oxazolamine ring to form a urea that has been reported for the demethylated congener aminorex. This suggests that 4-methyl substitution of the oxazoline ring may inhibit metabolism similar to the alpha-methyl substitution of beta-phenylethylamines.     

Disposition of methyl ethyl ketoxime in the rat after oral, intravenous and dermal administration

1. The disposition of 14C-methyl ethyl ketoxime (MEKO) was determined in the male F344 rat following oral, intravenous (i.v.) and dermal administration. 2. Oral doses of 2.7, 27 and 270 mg/kg were primarily excreted as CO2 (71-49%) in decreasing percentage as the dose increased. Excretion in urine (13-26%) and as volatiles (5-18%) increased as the dose increased. Five to 6% of the dose remained in the major tissues after 72 h. 3. An i.v. dose of 2.7 mg/kg was also principally excreted as CO2 (48.8%) with excretion in urine and as expired volatiles accounting for 21.4 and 11.4%, respectively. About 7% of the administered radioactivity remained in the tissues after 72 h. 4. Following dermal administration, 13 and 26% of a 2.7 and 270 mg/kg dose, respectively, were absorbed. Volatilization from the dose site prior to placement in the metabolism cage may account for the low absorption. 5. MEKO was biotransformed to at least five polar metabolites that could only be partially resolved by anion exchange chromatography. Incubation with glucuronidase, but not sulphatase, changed the urinary metabolic profile. Methyl ethyl ketone was a major component in the volatiles.     

Excretion kinetics of ifosfamide side-chain metabolites in children on continuous and short-term infusion

Ifosfamide (IFO) requires metabolic activation by hydroxylation of the ring system to exert cytotoxic activity. A second metabolic pathway produces the cytostatically inactive metabolites 2-dechloroethyl-ifosfamide (2-D-IFO) and 3-dechloroethyl-ifosfamide (3-D-IFO) under release of chloroacetaldehyde. This side-chain metabolism has been suggested to be involved in CNS- and renal toxicity. The total urinary excretion of ifosfamide and its metabolites was investigated during 23 cycles in 22 children at doses ranging from 400 mg/m2 to 3 g/m2. The kinetics of the excretion were compared following short-term and continuous ifosfamide infusion at a dosage of 3 g/m2. IFO and side-chain metabolites were analyzed by gas chromatography, the active metabolites by indirect determination of acrolein (ACR) and IFO mustard (IFO-M) with the NBP test. 59+/-15% of the applied dose could be recovered in the urine, 23+/-9% as unmetabolized IFO. The main metabolite was 3-D-IFO (14+/-4%) followed by isophosphoramide mustard (IFO-M) (13+/-4%) and 2-D-IFO (8+/-3%). Neither the total amount recovered nor the excretion kinetics of ifosfamide and side-chain metabolites showed obvious schedule dependency. The excretion kinetics of side-chain metabolites as well as unmetabolized IFO were nearly superimposable on short-term and continuous infusion. Even after 1-hour infusion there was a lag of 3 - 6 hours until dechloroethylation became relevant. Therefore, differences in toxicity and efficacy cannot be explained by an influence of the application time on the metabolic profile of ifosfamide.     

Metabolism of [14C]paracetamol and its interactions with aspitin in hamsters

1. The metabolism of [14C]paracetamol (150 mg/kg) and its interactions with aspirin (200 mg/kg) were studied in male hamsters. 2. Aspirin was found to slow the rate of paracetamol absorption from the gastro-intestinal tract, but did not affect the rate of elimination. 3. Metabolism studies showed that greater than 80% of the radioactivity was excreted in the urine in 24 h. Paper chromatography of the urine separated the radioactivity into five peaks, four of which were identified as paracetamol and its glucuronide, sulphate and mercapturate conjugates. 4. The other peak, comprising of less than 10% of the total radioactivity, was a mixture of two or more other metabolites. A major component was isolated and characterized as methyl 2-hydroxy-5-acetamidophenyl sulphone. 5. Aspirin inhibited the metabolism of paracetamol by the sulphate conjugation pathway.     

Biotransformation of an antihypertensive arylalkylamine analogue in the rat

1. The excretion and metabolism of N-[2-(3,4-dimethoxyphenyl)ethyl]-5-methoxy-N,alpha-dimethyl-2-(phenyl ethynyl) benzenepropanamine (RWJ-26240) in the Wistar rat has been investigated after a single oral dose of 14C-RWJ-26240 (50 mg/kg free base). 2. Plasma samples were obtained for 24 h after dosing and urine and faecal samples were collected over 8 days, and they accounted for 0.9 and 96% of the dose, respectively. 3. Representative samples of plasma, urine and faecal samples were purified for metabolite isolation and identification using HPLC, tlc, mass spectra (CI and EI), 1H-NMR and derivatization. 4. Unchanged RWJ-26240 plus 11 metabolites were identified and accounted for > 80% of the sample radioactivity. 5. Four metabolic pathways for RWJ-26240 are proposed; namely (1) N-demethylation, (2) O-demethylation, (3) phenyl hydroxylation and (4) N-dealkylation. Pathways 1-3 appeared to be quantitatively more important.     

Dose proportionality and comparison of single and multiple dose pharmacokinetics of fexofenadine (MDL 16455) and its enantiomers in healthy male volunteers

The pharmacokinetics and dose proportionality of fexofenadine, a new non-sedating antihistamine, and its enantiomers were characterized after single and multiple-dose administration of its hydrochloride salt. A total of 24 healthy male volunteers (31 +/- 8 years) received oral doses of 20, 60, 120 and 240 mg fexofenadine HCl in a randomized, complete four-period cross-over design. Subjects received a single oral dose on day 1, and multiple oral doses every 12 h on day 3 through the morning on day 7. Treatments were separated by a 14-day washout period. Serial blood and urine samples were collected for up to 48 h following the first and last doses of fexofenadine HCl. Fexofenadine and its R(+) and S(-) enantiomers were analysed in plasma and urine by validated HPLC methods. Fexofenadine pharmacokinetics were linear across the 20-120 mg dose range, but a small disproportionate increase in area under the plasma concentration-time curve (AUC) (< 25%) was observed following the 240 mg dose. Single-dose pharmacokinetics of fexofenadine were predictive of steady-state pharmacokinetics. Urinary elimination of fexofenadine played a minor role (10%) in the disposition of this drug. A 63:37 steady-state ratio of R(+) and S(-) fexofenadine was observed in plasma. This ratio was essentially constant across time and dose. R(+) and S(-) fexofenadine were eliminated into urine in equal rates and quantities. All doses of fexofenadine HCl were well tolerated after single and multiple-dose administration.     

In vivo versus in vitro produced bovine ova: similarities and differences relevant for practical application

1. Ortho-phenylphenol (OPP) was well absorbed in the male B6C3F1 mouse, with 84 and 98% of the administered radioactivity recovered in the 0-48-h urine of animals administered a single oral dose of 15 or 800 mg/kg respectively. High absorption and rapid elimination were also seen in the female and male F344 rat with 86 and 89% respectively of a single oral dose (27-28 mg/kg) found in the urine in 24 h. OPP was also rapidly eliminated from human volunteers following dermal exposure for 8 h (0.006 mg/kg), with 99% of the absorbed dose in the urine in 48 h. 2. Sulphation of OPP was found to be the major metabolic pathway at low doses in all three species, accounting for 57, 82 and 69% of the urinary radioactivity in the male mouse (15 mg/kg, p.o.), male rat (28 mg/kg, p.o.) and male human volunteers (0.006 mg/kg, dermal). OPP-glucuronide was also present in all species, representing 29, 7 and 4% of the total urinary metabolites in the low dose groups of mouse, rat and human volunteers respectively. 3. Conjugates of 2-phenylhydroquinone (PHQ) in these single-dose studies accounted for 12, 5 and 15% of the dose in mouse, rat and human, respectively. Little or no free OPP was found in any species. No free PHQ or PBQ was found in the mouse, rat or human (LOD = 0.1-0.6%). 4. A novel metabolite, the sulphate conjugate of 2,4'-dihydroxybiphenyl, was identified in rat and man, comprising 3 and 13% of the low dose respectively. 5. Dose-dependent shifts in metabolism were seen in the mouse for conjugation of parent OPP, indicating saturation of the sulphation pathway. Dose-dependent increases in total PHQ were also observed in mouse. 6. This study was initiated to elucidate a mechanistic basis for the difference in carcinogenic potential for OPP between rat and mouse. However, the minor differences seen in the metabolism of OPP in these two species do not appear to account for the differences in urinary bladder toxicity and tumour response between mouse and rat.