Biotransformation of 2-chloroaniline in the Fischer 344 rat: identification of urinary metabolites

1. The biotransformation of a single i.p. dose of [14C]2-chloroaniline (1.0 mmol/kg, approximately 60 microCi/rat) was investigated in the urine and faeces of the male Fischer 344 rat. 2. During 24 h, 53.1% of the administered radioactivity was eliminated into the urine, while < 1% of the radioactivity appeared in the faeces. 3. The major biotransformation pathways were para-hydroxylation and sulphate conjugation. 4-Amino-3-chlorophenyl sulphate was the major urinary metabolite comprising 31.6% of total urinary radioactivity. The para-hydroxylated metabolite, 4-amino-3-chlorophenol (10.8%), and its O-glucuronide conjugate (3.7%) were also urinary metabolites. The formation of direct conjugates of 2-chloroaniline, the N-sulphate and N-glucuronide, was significant with as much as 18.6 and 8.6%, respectively, of these metabolites excreted in the urine. The parent compound, 2-chloroaniline, accounted for 16.9% of urinary radioactivity. 4. N-Acetylated products were minor metabolites present in urine as 2-chloro-4-hydroxyacetanilide and its sulphate or glucuronide conjugate. Neither 2-chloroacetanilide nor its oxidation products, 2-chloroglycolanilide and 2-chlorooxanilic acid, were urinary metabolites.     

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.     

Pharmacokinetics, disposition and metabolism of 546C88 (L-NG-methylarginine hydrochloride) in rat and dog

1. 14C-546C88 (14C-L-NG-methylarginine hydrochloride) was administered to rat and dog as a single 5-min intravenous infusion at 1.7 mg/kg (20 mg/kg/h) to aid in the preclinical safety evaluation of the compound. 2. The distribution and elimination of parent compound from plasma was rapid in both species. 3. Drug-derived radioactivity was eliminated slowly. There was up to 39% of the dose retained in the carcasses at the end of the 7-day collection periods. The main route of elimination was as 14CO2 in the expired air. Less than 8% of the dose was excreted in the urine, and < 5% in the faeces. 4. Drug derived radioactivity was widely distributed throughout the body with highest concentrations in tissues with a high protein turnover, such as glandular tissue and liver. 5. 14C-546C88 appeared to be eliminated primarily by metabolism and subsequent putative amino acid catabolism, resulting in retention of drug-derived radioactivity in tissues, and ultimate elimination as 14CO2 in the expired air. Potential routes of metabolism of 546C88 have been identified.     

Metabolism and disposition of 14C-granisetron in rat, dog and man after intravenous and oral dosing

1. The disposition and metabolic fate of 14C-granisetron, a novel 5-HT3 antagonist, was studied in rat, dog, and male human volunteers after intravenous and oral administration. 2. Complete absorption occurred from the gastrointestinal tract following oral dosing, but bioavailability was reduced by first-pass metabolism in all three species. 3. There were no sex-specific differences observed in radiometabolite patterns in rat or dog and there was no appreciable change in disposition with dose between 0.25 and 5 mg/kg in rat and 0.25 and 10 mg/kg in dog. Additionally, there were no large differences in disposition associated with route of administration in rat, dog and man. 4. In rat and dog, 35-41% of the dose was excreted in urine and 52-62% in faeces, via the bile. Metabolites were largely present as glucuronide and sulphate conjugates, together with numerous minor polar metabolites. In man, about 60% of dosed radioactivity was excreted in urine and 36% in faeces after both intravenous and oral dosing. Unchanged granisetron was only excreted in urine (5-25% of dose). 5. The major metabolites were isolated and identified by MS spectroscopy and nmr. In rat, the dominant routes of biotransformation after both intravenous and oral dosing were 5-hydroxylation and N1-demethylation, followed by the formation of conjugates which were the major metabolites in urine, bile and plasma. In dog and man the major metabolite was 7-hydroxy-granisetron, with lesser quantities of the 6,7-dihydrodiol and/or their conjugates.     

Orally active inhibitors of human leukocyte elastase. II. Disposition of L-694,458 in rats and rhesus monkeys

The disposition of L-694,458, a potent monocyclic beta-lactam inhibitor of human leukocyte elastase, was studied in male Sprague-Dawley rats and rhesus monkeys. After iv dosing, L-694,458 exhibited similar pharmacokinetic parameters in rats and rhesus monkeys. The mean values for its plasma clearance, terminal half-life, and volume of distribution at steady state were 27 ml/min/kg, 1.8 hr, and 4.0 liters/kg in rats and 34 ml/min/kg, 2.3 hr, and 5 liters/kg in rhesus monkeys. The bioavailability of a 10 mg/kg oral dose was higher in rats (65%) than in rhesus monkeys (39%). In both species, concentrations of L-694,458 in plasma increased more than proportionally when the oral dose was increased from 10 mg/kg to 40 mg/kg. In monkeys a protracted plasma concentration-time profile was observed at 40 mg/kg, characterized by a delayed T(max) (8-24 hr) and a long terminal half-life (6 hr). [3H]L-694,458 was well absorbed after oral dosing to rats at 10 mg/kg, as indicated by the high recovery of radioactivity in bile (83%) and urine (6%) of bile duct-cannulated rats. Only approximately 5% or less of the radioactivity in bile, urine, and feces was a result of intact L-694,458, indicating that the compound was being eliminated by metabolism, followed by excretion of the metabolites in feces, via bile. Demethylenation of the methylenedioxyphenyl group resulting in the catechol was the primary metabolic pathway in human and rhesus monkey liver microsomes. In rat liver microsomes, the major metabolite was the N-oxide of the methyl-substituted piperazine nitrogen. In rats dosed iv and orally with [3H]L-694,458, concentrations of radioactivity were highest in the lung (the primary target tissue), adrenals, and liver. L-694,458 was unstable in rat blood and plasma, degrading via a pathway believed to be catalyzed by B-esterases and to involve cleavage of the beta-lactam ring and loss of the methylpiperazine phenoxy group. In vitro studies indicated that in human liver, L-694,458 was metabolized by CYP3A and 2C isozymes, and in both monkey and human liver microsomes the compound acted as an inhibitor of testosterone 6beta-hydroxylation.     

In vivo proliferation of oligodendrocyte progenitors expressing PDGFalphaR during early remyelination

2,4-Pentanedione (2,4-PD; CAS No. 123-54-6), an industrial chemical, was investigated for its comparative pharmacokinetics in male Fischer 344 rats by a single intravenous (i.v.) injection of (4.3, 43, 148.5, and 430 mg/kg), or a 6-hr nose-only inhalation exposure (400 ppm) to 14C-2,4-PD. For the i.v. route, the plasma concentration of 14C-2,4-PD-derived radioactivity declined in a biexponential fashion. The overall form of the 14C plasma concentration-time curves and derived pharmacokinetic parameters indicated that dose-linear kinetics occurred in the i.v. dose range 4.3-148.5 mg/kg, but not with 430 mg/kg. Metabolism of 2,4-PD was quite rapid as the concentration of unmetabolized 2,4-PD declined steadily to undetectable after 8 hr. 14C-2,4-PD derived radioactivity was eliminated mainly as 14CO2 and in urine. For the 4.3, 43 and 148.5 mg/kg doses 14CO2 elimination was relatively constant (36.8, 38.8 and 42.3% in 48 hr samples respectively) and greater than urinary excretion (17.9, 14.3 and 29.6%; 48 hr specimens). At 430 mg/kg i.v. there was a reversal of the excretion pattern, with urine 14C excretion (54.7%) becoming greater than that for 14CO2 (27.3%). Excretion in expired volatiles and feces was small. Radiochromatograms of urine showed free 2,4-PD in the 12 hr sample, together with 7 other metabolites. Free 2,4-PD and 6 of the metabolites decreased or were not detectable in a 24 or 48 hr urine sample, but one peak (retention 7.9 min) increased progressively to become the major fraction (97%). Nose-only exposure to 400 ppm 14C-2, 4-PD produced a mean decrease in breathing rate of 20.1%, which was constant and sustained throughout exposure, due to a lengthening of the expiratory phase of the respiratory cycle. 14C-2,4-PD was rapidly absorbed during the first 3 hr of exposure, then began to plateau, but did not reach a steady state. Postexposure elimination of 14C from plasma followed a biexponential form with a t1/2 for the terminal disposition phase of 30.72 hr. Plasma unmetabolized 2,4-PD was present throughout the whole of the exposure phase, but was significantly less than total 14C. Postexposure, plasma unmetabolized 2,4-PD declined rapidly to undetectable concentrations by 12 hr. Radiolabel excretion was approximately equivalent in urine (37.6%) and expired 14CO2 (36.3%). Urine radiochromatograms showed a minor 2,4-PD contaminant (0.6-5.9% over 48 hr), along with 7 other peaks probably representing metabolites. As with the 148.5 mg/kg i.v. dose, the major metabolite peak was at 7.8 min retention, increasing from 41.1% (12 hr) to 62.8% (48 hr). Immediately postexposure, radioactivity was present in all tissues examined, but on a concentration basis (microgram equiv/g) there was no preferential accumulation of 14C in any tissue or organ. On a total organ basis, highest contents were in liver and kidney, presumably related to the metabolism and excretion of 2,4-PD. By 48 hr postexposure, concentrations had decreased in all tissues except fat, presumably due to the lipophilicity of 14C residues. The profile of the plasma-time radioactivity curves, and the presence of residual radioactivity in tissues at 48 hr postexposure, suggests that a cumulative process could occur with frequent repeated exposures.     

Pharmacology and toxicology of artelinic acid: preclinical investigations on pharmacokinetics, metabolism, protein and red blood cell binding, and acute and anorectic toxicities

The pharmacokinetics, metabolism, protein binding, red blood cell (RBC) binding, stability in vitro, and acute and anorectic toxicity of artelinic acid (ARTL) were investigated in various animal species and human blood samples. Absorption and distribution following 10 mg/kg intramuscular or oral administration in dogs and rats were very rapid with t1/2 0.12-0.54; there were also a high AUC (11,262 ng/h/mL) and Vss (9.5 L/kg), low CL (15 mL/min/kg) and long elimination time (t1/2 = 2.6 h), compared with rat data. Oral bioavailability of ARTL was 79.7% in dogs and 30.1% in rats. The conversion of ARTL to dihydroartemisinin (DART) in dogs (0.1-0.5% of total dose) after 3 routes of administration (intravenous, intramuscular and oral) was 10-fold lower than that in rats. In rats dosed with [14C]ARTL, unchanged ARTL accounted for less than 13% of the total radioactivity after all 3 administration routes, suggesting that ARTL was extensively biotransformed. The half-lives of total radioactivity (21-49 h) in urine were much longer than that of unchanged ARTL in plasma (1.4-3.7 h), indicating that some long-lasting metabolites of ARTL were formed in rats. The mass balance data showed that 77-83% of total radioactivity was recovered in urine and faeces. High binding capacity (79-95%) and low binding affinity (1.1-9.3 x 10-7 M) of ARTL were measured in rat, rabbit, dog, monkey and human plasma. The RBC/plasma ratios of [14C]ARTL were 0.35 and 0.44 for dog and human plasma, respectively. ARTL was much more stable than artesunic acid (ARTS) in rat and dog plasma, and both ARTL and ARTS were more stable in dog plasma than in rat plasma in vitro. The 50% lethal dose (LD50) of ARTL in rats was about 535 mg/kg. Multiple intramuscular dosing for 7 d of 50 mg/kg/d of ARTL caused mild anorectic toxicity compared to ARTS in rats. In contrast to 4 other artemisinin derivatives, ARTL seems to be a good antimalarial candidate as it has the highest plasma concentration, the highest binding capacities in RBC, the highest oral bioavailability, the longest elimination half-life, the lowest metabolism rate and the lowest toxicity at equivalent dose levels.     

The biodegradation of the surfactant undecyl sulphate

1. The metabolism of the odd-numbered carbon chain surfactant, potassium undecyl [35S]sulphate in the rat was investigated. 2. The major route for elimination of radioactivity was the urine, regardless of the route of administration. 3. The surfactant was extensively degraded in vivo to yield propionic acid 3-[35S]sulphate, the major radioactive component in urine. A second urinary metabolite was identified tentatively as pentanoic acid 5-[35S]sulphate. 4. Whole-body autoradiography revealed the liver as the major site of metabolism. 5. The nature of the metabolic products of undecyl sulphate suggest that it is bio-degraded by initial omega-oxidation followed by beta-oxidation.     

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.     

Immediate implantation into the posterior maxilla after antroplasty: the Cranin-Russell Operation

KW-2149 is a new derivative of mitomycin C (MMC). The plasma concentrations, distribution, metabolism, and excretion of [3H]-KW-2149 in normal and tumor-bearing mice after i.v. administration of 16.6 mg/kg were investigated. The plasma radioactivity decreased biexponentially after i.v. administration in normal mice. However, the unchanged drug disappeared rapidly, showing a half-life (t1/2) of 9.7 min, which was shorter than MMC's (18 min). The radioactivity was excreted in mouse urine (33%) and feces (58%) within 144 h. High radioactivity was distributed in the gallbladder, liver, kidney, pancreas, and lung at 1 h after i.v. administration to normal mice. The tumor concentration was lower than the plasma or blood concentration. The lowest radioactivity was observed in the brain. The metabolic rate of KW-2149 was very rapid. The methyl sulfide form (M-16), the symmetrical disulfide dimer (M-18), and the albumin conjugate were detected in plasma, which possessed anticellular activity. The specific anticellular activity of these compounds against uterine carcinoma (HeLa S3) was 1/100, 1, and 1/20 respectively, as compared with that of KW-2149.     

Chemopreventive efficacies of aspirin and sulindac against lung tumorigenesis in A/J mice

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs. In this study, we demonstrated the efficacy of aspirin to inhibit lung tumorigenesis in A/J mice. Lung tumors (9.9 tumors/mouse) were induced by the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), administered in drinking water between week 0 and week +7. Groups of mice were fed sulindac (123 mg/kg diet), acetylsalicylic acid (ASA; 294 mg/kg), non-buffered Aspirin (294 mg/kg) or buffered Aspirin (294 mg/kg) in AIN-76A diet from week -2 to the end of the bioassay (week +23). These doses are comparable to the maximal doses recommended for humans. ASA and non-buffered Aspirin were the most effective inhibitors and reduced lung multiplicities by 60 and 62%, respectively. Sulindac inhibited lung tumor multiplicity by 52%. Inhibition by buffered Aspirin was not statistically significant. We evaluated the efficacies of NSAIDs to inhibit NNK activation by h1A2 v2 cells expressing human P-450 1A2. Salicylates, at doses of 500 microM and 1 mM, had no effect on NNK activation. Sulindac and its sulfide and sulfone metabolites (1 mM) inhibited NNK metabolism by 90, 92 and 65%, respectively. We observed a 76% inhibition with SKF 525A, a P-450 inhibitor. Taken together, these results indicate that salicylates and sulindac could be equally effective as chemopreventive agents, but they could differ in their mode of action.     

Road traffic mortality in Victoria: an exploratory investigation into successful strategies

The recovery of radioactivity from plasma, urine and feces was determined in rats after administration of oral and intravenous doses (200 mg/kg) of 14C-labeled sodium gamma-hydroxybutyric acid. Very small portions of the radioactive dose were recovered in the urine (5.5%, oral; 7.1%, intravenous) and feces (1.5% oral; 0.6%, intravenous) collected between 0-48 hours after drug administration. Considerable levels of radioactivity were found in the plasma after oral dosing. The area under the plasma radioactivity time curve after an oral dose was found to be 65% of that observed after an equivalent intravenous dose. This value is much larger than the relative area value (8%) calculated on the basis of free gamma-hydroxybutyric acid. Results of this study strongly indicate that first-pass metabolism, rather than lack of absorption, is responsible for the apparently poor oral bioavailability of gamma-hydroxybutyric acid.     

Studies on the toxicology of hexachlorobenzene. II. Identification and determination of metabolites

Female rats were dosed intraperitoneally with 14C-hexaxhlorobenzene. The drug was administered on 2 or 3 occasions. The total doses amounted to 260 and 390 mg/kg 14C-hexachlorobenzene, respectively. Urine and feces from the animals were collected over a period of 4 weeks after the first injection. Both excreta and some tissues of the animals were examined for their content of radioactivity and for hexachlorobenzene and its metabolites. Gas chromatography, isotope dilution analysis, and combined gas chromatography-mass spectrometry were used to identify the metabolites of hexachlorobenzene. In urine pentachlorophenol, tetrachlorohydroquinone, and pentachlorothiophenol were present as major metabolites. One of the isomers of tetrachlorothiophenol was present as a minor metabolite. In the feces pentachlorophenol and pentachlorothiophenol only were identified. At the end of the experiment, carbon-14 excreted with urine and feces amounted to 7% and 27%, respectively, of the radioactivity administered. More than 90% of carbon-14 excreted in urine was contained in the major metabolites. In the feces about 30% of the excreted radioactivity was bound to metabolites and about 70% was contained in the unchanged drug, while in the tissues of the animals only pentachlorophenol was detected in measurable amounts, accounting for 10% of label in blood and less than 0.1% of carbon-14 determined in body fat. Total radioactivity contained in the metabolites detected in the animal body and in the excreta at the end of the experiment accounted for about 16% of the administered radioactivity.     

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.     

Pharmacokinetics, oral bioavailability, and metabolism in mice and cynomolgus monkeys of (2'R,5'S-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl] cytosine, an agent active against human immunodeficiency virus and human hepatitis B virus

(2'R,5'S-)-cis-5-Fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl] cytosine (524W91) is a nucleoside analog with potent anti-human immunodeficiency virus and anti-human hepatitis B virus activities in vitro. The pharmacokinetics and bioavailability of 524W91 after oral dosing were studied in mice dosed with 10, 100, and 600 mg of 524W91 per kg of body weight by the oral and intravenous routes. Cynomolgus monkeys were dosed with 10 and 80 mg of 524W91 per kg. In both species, the clearance of 524W91 was rapid, via the kidney, and was independent of dose. In monkeys, the total body clearance of 10 mg of 524W91 per kg was 0.7 +/- 0.1 liter/h/kg, and the volume of distribution at steady state was 0.8 +/- 0.02 liter/kg. The terminal elimination half-life was 1.0 +/- 0.2 h. The absolute bioavailability after oral dosing was 63% +/- 4% at 10 mg/kg. Concentrations of 524W91 in the cerebrospinal fluid were 4% +/- 0.7% of the corresponding levels in plasma. In mice, the total clearance of 10 mg of 524W91 per kg was 2.3 liters/kg/h, and the volume of distribution at steady state was 0.9 liter/kg. Absolute bioavailability in mice after oral dosing was 96% at a dose of 10 mg/kg. The metabolism of orally administered [6-3H]524W91 was studied in cynomolgus monkeys at a dose of 80 mg/kg and in mice at a dose of 120 mg/kg. Monkeys excreted 41% +/- 6% of the radioactive dose in the 0- to 72-h urine, 33% +/- 10% in the feces, and 10% +/- 7% in the cage wash. Unchanged 524W91 was 64% of the total radiolabeled drug recovered in the urine. The glucuronide was a minor urinary metabolite. 5-Fluorouracil was not detected (less than 0.02% of the dose). Mice dosed orally with 120 mg of [6-3H]524W91 per kg excreted 67% +/- 7% of the radiolable in the )- to 48-h urine. Small amounts of the 3' -sulfoxide and glucuronide metabolites were observed in the urine, but 5-fluorouracil was not detected. Good bioavailability after oral dosing and resistance to metabolism recommend 524W91 for further preclinical evaluation.     

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.     

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.     

Oligosaccharide release from frozen and paraffin-wax-embedded archival tissues

Rats (Sprague-Dawley), submitted to a mechanical noxious stimulus (paw pressure), were tested to determine 1) the antinociceptive effects of p.o. (200, 400 and 800 mg/kg), i.v. (50, 100, 200 and 300 mg/kg) and intrathecal (i.t.) (100 and 200 micrograms/rat) administrations of paracetamol; 2) the influence of i.t. administered tropisetron, a 5-hydroxytryptamine3 (5-HT3) receptor antagonist (0.5, 1 or 10 micrograms/rat) on paracetamol-induced antinociception; 3) the influence of indomethacin (25 mg/kg s.c.), naloxone (10 micrograms/rat i.t.) and yohimbine (1 mg/kg i.v.) on the effect of paracetamol (200 mg/kg i.v.) to determine the involvement of prostaglandins, opioids and alpha-2 adrenoceptors. The displacement by paracetamol of radioligand binding to various receptors was also investigated. Paracetamol induced a significant antinociceptive effect after p.o., i.v. and i.t. administration. A total inhibition of the effect of paracetamol, administered p.o. or i.t., occurred at the dose of 0.5 microgram/rat of tropisetron, whereas 10 micrograms/rat of this antagonist was needed to totally inhibit the action of i.v. administered paracetamol. Indomethacin, naloxone and yohimbine failed to modify paracetamol antinociceptive action. In vitro studies failed to show any binding of paracetamol to 5-HT3 and several other receptors and to 5-HT uptake sites. It is concluded that paracetamol has a central antinociceptive effect, based on an indirect involvement of spinal 5-HT3 receptors.     

Synthesis and excretion profile of 1,4-[14C]phenylenebis(methylene)selenocyanate in the rat

1,4-Phenylenebis(methylene)selenocyanate (p-XSC) inhibits chemically induced tumors in several laboratory animal models. To understand its mode of action, we synthesized p-[14C]XSC, examined its excretion pattern in female CD rats and also the nature of its metabolites. p-[14C]XSC was synthesized from alpha,alpha-dibromo-p-[ring-14C]xylene in 80% yield. The excretion profile of p-[14C]XSC (15.8 mg/kg body wt, 200 microCi/rat, oral administration, in 1 ml corn oil) in vivo was monitored by measuring radioactivity and selenium content. On the basis of radioactivity, approximately 20% of the dose was excreted in the urine and 68% in the feces over 3 days. The cumulative percentages of the dose excreted over 7 days were 24% in urine and 75% in feces, similar to excretion rates of selenium. According to selenium measurement, <1% of the dose was detected in exhaled air; radioactivity was not detected. Only 15% of the dose was extractable from the feces with EtOAc and was identified as tetraselenocyclophane (TSC). Most of the radioactivity remained tightly bound to the feces. Approximately 10% of this bound material converted to TSC on reduction with NaBH4. Organic soluble metabolites in urine did not exceed 2% of the dose; sulfate (9 % of urinary metabolites) and glucuronic acid (19.5% of urinary metabolites) conjugates were observed but their structural identification is still underway. Co-chromatography with a synthetic standard led to the detection of terephthalic acid (1,4-benzenedicarboxylic acid) as a minor metabolite. The major urinary conjugates contained selenium. Despite the low levels of selenium in the exhaled air, the reductive metabolism of p-XSC to H2Se cannot be ruled out. Identification of TSC in vivo indicates that a selenol may be a key intermediate responsible for the chemopreventive action of p-XSC.