The metabolism of 14C-tazadolene succinate in the dog.

1. Beagle dogs dosed orally with 14C-tazadolene succinate excreted much of the dose in the urine (mean 63.1% in 5 days with most excreted in the first 24 h). A lesser proportion of the dose was excreted in the faeces (mean 20.7%) and again most of this was voided in the first 24 h. 2. Four metabolites were identified and quantified in the urine, namely 3-hydroxy-(M1), 4-hydroxy- (M2a), and 3-methoxy-4-hydroxy-tazadolene (M2b) and N-[2-(phenylmethylene)cyclohexyl]-beta-alanine (M3). 3. In the 24 h urine, M2a and b glucuronides accounted for 17.7% dose, unconjugated M2a and b for 11.3%, and M3 for 18.3%. Insufficient M1 was present to be quantified. The same metabolites were seen in the 24 h faeces, but at lower concn. Thus M2a and b glucuronides, M2a and b, and M3 were 3.2%, 4.9% and 3.5% dose respectively. 4. All three phenols were present in plasma as their glucuronides as well as the beta-alanine derivative. They all had the same tmax of 2 h and t1/2 lambda 1 of the order of 1 h.     

The Fate of [14C]Saccharin in Man,Rat and Rabbit and of 2-Sulphamoyl[14C]benzoic Acid in the Rat

1. [¹⁴C]Saccharin administered orally was excreted entirely unchanged by rats on a normal diet and by rats on a 1% and 5% saccharin diet for up to 12 months. Some 90% dose was excreted in 24?h, about 70–80% in urine and 10–20% in faeces. No metabolite was detected in the excreta by chromatography or reverse isotope dilution. No ¹⁴CO₂ was found in the expired air and no ¹⁴CO₃^2- or 2-sulphamoylbenzoic acid in the urine.

2. When [¹⁴C]saccharin was injected into bile-duct cannulated rats kept on a normal diet or on a 1% saccharin diet for 19 and 23 months, 0.1–0.3% dose appeared in the bile in 3?h and no more at 24?h after dosing. Most of the saccharin was excreted in the urine, 0.6% appearing in the faeces.

3. [¹⁴C]Saccharin given orally to rabbits kept on untreated water and on water containing 1% saccharin for 6 months was excreted unchanged, 60–80% in 24?h, with 70% in urine and 3–11% in faeces.

4. [3-¹⁴C]Saccharin taken orally was excreted unchanged mainly in urine (85–92% in 24?h) by 3 adult humans both before and after taking 1 g of saccharin daily for 21 days. No metabolite of saccharin was found.

5. When [¹⁴C]saccharin was administered orally to pregnant rats on the 21st day of gestation only at most 0.6% of dose entered the foetuses. The ¹⁴C cleared more slowly from the urinary bladder than from other maternal or foetal tissues.

6. Saccharin was not metabolized in vitro by liver microsomal preparations or faecal homogenates from rats kept on a normal diet or on a 1% saccharin diet for two years.

7. 2-Sulphamoyl[¹⁴C]benzoic acid given orally to rats was excreted unchanged more slowly than saccharin. It was not cyclized to saccharin in vivo.     

Absorption,metabolism and excretion of darexaban (YM150), a new direct factor Xa inhibitor in humans

1.?The absorption, metabolism and excretion of darexaban (YM150), a novel oral direct factor Xa inhibitor, were investigated after a single oral administration of [¹⁴C]darexaban maleate at a dose of 60?mg in healthy male human subjects.

2.?[¹⁴C]Darexaban was rapidly absorbed, with both blood and plasma concentrations peaking at approximately 0.75?h post-dose. Plasma concentrations of darexaban glucuronide (M1), the pharmacological activity of which is equipotent to darexaban in vitro, also peaked at approximately 0.75?h.

3.?Similar amounts of dosed radioactivity were excreted via faeces (51.9%) and urine (46.4%) by 168?h post-dose, suggesting that at least approximately half of the administered dose is absorbed from the gastrointestinal tract.

4.?M1 was the major drug-related component in plasma and urine, accounting for up to 95.8% of radioactivity in plasma. The N-oxides of M1, a mixture of two diastereomers designated as M2 and M3, were also present in plasma and urine, accounting for up to 13.2% of radioactivity in plasma. In faeces, darexaban was the major drug-related component, and N-demethyl darexaban (M5) was detected as a minor metabolite.

5.?These findings suggested that, following oral administration of darexaban in humans, M1 is quickly formed during first-pass metabolism via UDP-glucuronosyltransferases, exerting its pharmacological activity in blood before being excreted into urine and faeces.     

Sex differences in the metabolism and excretion of nilvadipine,a new dihydropyridine calcium antagonist,in rats

1. The metabolic profiles of nilvadipine in the urine and bile of male and female rats were studied after i.v. dosing with 1?mg/kg of the ¹⁴C-labelled compound.

2. Excretion rates of the dosed radioactivity in male and female rats, respectively, in the first 48?h were 8.41% and 59.1% in bile, 12.0% and 36.9% in urine, and 2.5% and 3.6% in faeces.

3. Comparison of biliary and urinary excretion for each radioactive metabolite after dosing with ¹⁴C-nilvadipine, showed marked sex-related differences in the excretion routes of several metabolites. In male rats, metabolite M3, having a free 3-carboxyl group on the pyridine ring, was not excreted in urine, but in female rats urinary excretion of M3 accounted for 4.7% of the dose. One reason for the lower urinary excretion of radioactivity by males than by females was that the main metabolite, M3, was not excreted in the urine of the male rats.

4. To clarify the sex difference in the route of excretion of M3, this metabolite (M3) was given i.v. to rats. No excretion of the metabolite was observed in urine of male rats within 24?h but, in marked contrast, 41.5% of the dose was excreted in urine of females in the same period.     

The Disposition and Metabolism of 3',4',7-Tri-O-(β-hydroxyethyl) rutoside and 7-Mono-O-(β-hydroxyethyl)rutoside in the Mouse

1. Following intravenous administration of 3',4',7-tri-O-(β-hydroxy[¹⁴C₂]ethyl)rutoside or 7-mono-O-(β-hydroxy[¹⁴C₂]ethyl)rutoside to male mice, 68% of the dose of each is excreted in faeces as the corresponding hydroxyethyl-quercetin within 72?h of dosage. Mean urinary excretions of mono- and tri-hydroxyethylrutosides in 72?h were 27 and 21% respectively. Unchanged rutosides and their glucuronides were detected in urine.

2. In biliary-cannulated animals, the mean biliary excretion of both tri- and mono-hydroxyethylrutosides was 71%, in 24?h of dosage. In both cases most ¹⁴C was excreted in 3?h, as unchanged rutosides and glucuronide conjugates.

3. Fall of blood ¹⁴C concn. was rapid for both compounds. Neither compound was detected in brain but there was short-term accumulation in liver and kidney, and 2-3?h after dosage, most ¹⁴C for both compounds was associated with the gastro-intestinal contents.

4. Animals killed 72?h after dosage of either compound contained <7% of dose, mostly in the color and caecal contents.

5. Foetuses removed 3?h after dosage of either compound to the dams did not contain ¹⁴C; foetuses removed 5 min after dosage contained low levels of ¹⁴C, substantially below the maternal blood level and equiv. to <0·1% of dose in each case. No ¹⁴C was detected in amniotic fluid.     

Metabolism of o-[methyl-14C]toluidine in the F344 rat

1. Following a single dose (400?mg/kg s.c.) of o-[methyl-¹⁴C]toluidine to male F344 rats, 56% of the ¹⁴C was recovered in the 24?h urine, 2–3% in the faeces and 1% as exhaled ¹⁴CO₂. After 48h, 83.9% of the ¹⁴C appeared in the urine, 3.3% in the faeces and 1.4% was exhaled.

2. Ether-extractable urinary metabolites were separated by?h.p.l.c. and identified as: o-toluidine (5.1% dose); azoxytoluene (0.2%); o-nitrosotoluene (≤0.1%); N-acetyl-o-toluidine (0.2%); N-acetyl-o-aminobenzyl alcohol (0.3%); 4-amino-m-cresol (0.6%); N-acetyl-4-amino-m-cresol (0.3%); anthranilic acid (0.3%) and N-acetylanthranilic acid (0.3%).

3. Acid-conjugated urinary metabolites (51% of dose), separated by paper electrophoresis and by Sephadex LH-20 chromatography, were identified as sulphates of 4-amino-m-cresol (27.8% dose), N-acetyl-4-amino-m-cresol (8.5%), and 2-amino-m-cresol (2.1%), and glucuronides of 4-amino-m-cresol (2.6%), N-acetyl-4-amino-m-cresol (2.1%), and N-acetyl-o-aminobenzyl alcohol. Evidence for a double acid conjugate of 4-amino-m-cresol was also found.

4. These results show that N-acetylation and hydroxylation at the 4 position of o-toluidine are major metabolic pathways in the rat. Minor pathways include hydroxylation at the 6 position, oxidation of the methyl group and oxidation of the amino group. Sulphate conjugates predominate over glucuronides by a ratio of 6:1.     

Metabolism and disposition of the dipeptidyl peptidase IV inhibitor teneligliptin in humans

Abstract

1. The absorption, metabolism and excretion of teneligliptin were investigated in healthy male subjects after a single oral dose of 20?mg [¹⁴C]teneligliptin.

2. Total plasma radioactivity reached the peak concentration at 1.33?h after administration and thereafter disappeared in a biphasic manner. By 216?h after administration, ≥90% of the administered radioactivity was excreted, and the cumulative excretion in the urine and faeces was 45.4% and 46.5%, respectively.

3. The most abundant metabolite in plasma was a thiazolidine-1-oxide derivative (designated as M1), which accounted for 14.7% of the plasma AUC (area under the plasma concentration versus time curve) of the total radioactivity. The major components excreted in urine were teneligliptin and M1, accounting for 14.8% and 17.7% of the dose, respectively, by 120?h, whereas in faeces, teneligliptin was the major component (26.1% of the dose), followed by M1 (4.0%).

4. CYP3A4 and FMO3 are the major enzymes responsible for the metabolism of teneligliptin in humans.

5. This study indicates the involvement of renal excretion and multiple metabolic pathways in the elimination of teneligliptin from the human body. Teneligliptin is unlikely to cause conspicuous drug interactions or changes in its pharmacokinetics patients with renal or hepatic impairment, due to a balance in the elimination pathways.     

The Effect of Route of Administration on the Metabolic Fate of Terbutaline in the Rat

Abstract

1. The metabolic fate of [³H]terbutaline has been investigated in rats after oral, subcutaneous, intraperitoneal and intraportal administration (5 mg per kg).

2. About half the administered radioactivity was excreted in the urine and the remainder in faeces regardless of route of administration. Urinary excretion was essentially complete in 24 h, but an additional 10% of the dose was excreted in the 24–48 h faeces.

3. Only one metabolite, a glucuronide conjugate of terbutaline, was excreted in the urine along with unchanged drug. About 3% of the dose was excreted unchanged in urine following oral administration. Ratios of terbutaline glucuronide to free drug were 1 : 1, 2 : 1 and 13 : 1 after subcutaneous, intraperitoneal or intraportal, and oral administration respectively, suggesting that the orally administered drug is extensively conjugated in the intestinal mucosa.

4. Measurement of the mobility-pH profile by high-voltage paper electrophoresis was utilized to characterize the conjugate.     

Meeting of the Drug Metabolism Group: Significance of Drug Metabolism and Disposition in Patient Therapy

1. ¹⁴C-Labelled benzoic acid, salicylic acid and 2-naphthylacetic acid were administered orally to horses, and urinary metabolites investigated by chromatographic and mass spectral techniques.

2. [¹⁴C] Benzoic acid (5?mg/kg) was eliminated rapidly in the urine, and quantitatively recovered in 24?h. The major urinary metabolite was hippuric acid (95% of dose) with much smaller amounts of benzoic acid, benzoyl glucuronide and 3-hydroxy-3-phenylpropionic acid. Administration of [ring-D₅]benzoic acid together with [¹⁴C]benzoic acid to a pony permitted the mass spectral determination of metabolites of the exogenous benzoic acid metabolites in the presence of the same endogenous compounds.

3. [¹⁴C]Salicylic acid (35?mg/kg) was eliminated rapidly in the urine, 98% of the ¹⁴C dose being excreted in 24?h. The major excretion product was unchanged salicylate (94% of dose). Gentisic acid, salicyluric acid and the ester and ether glucuronides of salicylic acid were very minor metabolites.

4. 2-Naphthyl[¹⁴C]acetic acid (2?mg/kg) was excreted very slowly in the urine, with 53 and 77% of the ¹⁴C dose being recovered in six days. 2-Naphthylacetylglycine was the major metabolite (26 and 38% dose) and in addition, the glucuronic acid and taurine conjugates were excreted together with unchanged 2-naphthylacetic acid.

5. This study has shown that the horse can utilize glycine, taurine and glucuronic acid for conjugation of xenobiotic carboxylic acids, and that the relative extents of these pathways are governed by the structure of the carboxylic acid.     

The Disposition and Metabolism of Amodiaquine in Small Mammals

1. 7-Chloro-4-(3′-diethylamino-4′-hydroxyanilino)quinoline (amodiaquine) labelled with ¹⁴C has been synthesized and administered in single doses to rats including bile-duct-cannulated rats, to guinea-pigs and to mice, by oral or parenteral routes.

2. Amodiaquine was extensively and rapidly absorbed from the rat intestinal tract. Excretion of total radioactivity from rats and guinea pigs was slow and prolonged and was <50% dose in 9 days. Excretion of ¹⁴C was predominantly in faeces of rats after oral and i.p. dosage, and guinea-pigs after i.p. dosage. Radioactivity in rat and guinea-pig urine was <11% dose.

3. Biliary excretion of ¹⁴C following oral or i.v. dosage to rats was 21% dose in 24?h.

4. Amodiaquine was extensively metabolized and conjugated with <10% dose excreted unchanged in urine or bile. Two major basic metabolites in rat urine were tentatively identified as the mono- and bis-desethyl amines.

5. 7-Chloro-4-(4′-diethyl-1′-methylbutylamino)quinoline (chloroquine) was excreted largely unchanged in urine of rats after oral or parenteral administration of single doses, with <5% dose excreted in rat bile in 24?h.     

Absorption,distribution, metabolism and excretion (ADME) of the ALK inhibitor alectinib: results from an absolute bioavailability and mass balance study in healthy subjects

1.?Alectinib is a highly selective, central nervous system-active small molecule anaplastic lymphoma kinase inhibitor.

2.?The absolute bioavailability, metabolism, excretion and pharmacokinetics of alectinib were studied in a two-period single-sequence crossover study. A 50?μg radiolabelled intravenous microdose of alectinib was co-administered with a single 600?mg oral dose of alectinib in the first period, and a single 600?mg/67?μCi oral dose of radiolabelled alectinib was administered in the second period to six healthy male subjects.

3.?The absolute bioavailability of alectinib was moderate at 36.9%. Geometric mean clearance was 34.5?L/h, volume of distribution was 475?L and the hepatic extraction ratio was low (0.14).

4.?Near-complete recovery of administered radioactivity was achieved within 168?h post-dose (98.2%) with excretion predominantly in faeces (97.8%) and negligible excretion in urine (0.456%). Alectinib and its major active metabolite, M4, were the main components in plasma, accounting for 76% of total plasma radioactivity. In faeces, 84% of dose was excreted as unchanged alectinib with metabolites M4, M1a/b and M6 contributing to 5.8%, 7.2% and 0.2% of dose, respectively.

5.?This novel study design characterised the full absorption, distribution, metabolism and excretion properties in each subject, providing insight into alectinib absorption and disposition in humans.     

Disposition of bemitradine,a Renal Vasodilator and Diuretic,in Man

1. ¹⁴C-Bemitradine (50 mg) was rapidly and efficiently absorbed (β89%) in man following a single oral dose, as a solution in gelatine capsules. Peak ¹⁴Clevels of 895 ± 154 ng equiv./ml (mean ± S.E.M.) were reached within 2h, and declined with half-lives of 1·07 ± 0·25 and 13·0± 5·6h.

2. No bemitradine was detected in plasma, but peak concn. (124±29ng/ml) of its desethyl metabolite were reached at 1·05±0·28h, and declined with a half-life of 1·32±0·08h.

3. Desethylbemitradine was rapidly metabolized to its ether glucuronide, a phenol and a dihydrodiol which were also present as glucuronide conjugates. The glucuronides were the major compounds in plasma from 2h after drug administration.

4. Excretion in 5 days amounted to 88·8±2·3% and 10·4±2·1% dose in urine and faeces respectively. No bemitradine or desethylbemitradine were excreted unchanged. 8-(2-Hydroxyethyl)-7-(3,4-dihydroxycyclohexa-l,5-dienyl)-l,2,4-triazolo-l,5c-pyrimidine-5-amine (E; 17% dose); 8-(2-hydroxyethyl)-7-(4-hydroxyphenyl)-l,2,4-triazolo-1.5c-pyrimidine-5-amine (F; 4% dose), their glucuronides (A, 19% dose and B, 6% dose respectively), desethylbemitradine glucuronide (D, 25% dose) and an unidentified metabolite (C, 12% dose) were excreted in urine. Compound F was the major faecal metabolite.     

The Metabolism of Terbutaline in Dog and Rat

Abstract

1. The metabolic fate of [³H]terbutaline has been studied in dog after oral, intravenous and subcutaneous administration and in rat after oral and intravenous administration. In 3–4 days the dog excreted 75% of the dose in the urine after oral administration and more than 90% after intravenous or subcutaneous administration; the remainder was in the faeces. The rat in 24 h excreted about 13% in the urine and 61% in the faeces after oral administration and 48% in the urine and 35% in the faeces after intravenous administration.

2. After oral administration of [³H]terbutaline, the time course of radioactivity concentration was the same in lung, heart and serum; low levels of unchanged drug were found in all tissues. After intravenous administration, the concentration of unchanged drug was higher in lung and heart than in serum.

3. In dog, 1·7% of an intravenous dose was excreted into bile in 6 h. In rat, about 37% of the dose was recovered in the bile during 12 h.

4. Enzymic hydrolysis of urine showed that terbutaline is metabolized by conjugation, forming a glucuronide in rat but probably a sulphate in dog.     

Metabolism of flumecinol in humans

1. The metabolism of ¹⁴C-flumecinol (3-trifluoromethyl-α-ethyl-benzhydrol) was studied in volunteers after a single oral dose of 100mg (11.1 MBq; 300μCi). Radioactivity excreted in urine was 78.8 ± 6.0% of dose and in faeces was 12.0 ± 5.3% dose in 120h.

2. Unchanged flumecinol was not excreted in urine, but was present in faeces unconjugated (1.2% dose) and as conjugates of glucuronic and sulphuric acids (10.8% dose).

3. Enzymic hydrolysis showed that all urinary metabolites were conjugated with glucuronic and/or sulphuric acids (77.8% dose). Unconjugated urinary metabolites were not found.

4. The major route of flumecinol metabolism was hydroxylation of the alkyl side chain and/or the phenyl group followed by conjugation.

5. Both the CF₃-group and the skeleton of the original compound remained intact during metabolism.     

Disposition,metabolism and mass balance of delafloxacin in healthy human volunteers following intravenous administration

Abstract

1. The pharmacokinetics and disposition of delafloxacin was investigated following a single intravenous (300?mg, 100?µCi) dose to healthy male subjects.

2. Mean C_max, AUC_0–∞, T_max and t_1/2 values for delafloxacin were 8.98?µg/mL, 21.31?µg?h/mL, 1?h and 2.35?h, respectively, after intravenous dosing.

3. Radioactivity was predominantly excreted via the kidney with 66% of the radioactive dose recovered in the urine. Approximately 29% of the radioactivity was recovered in the faeces, giving an overall mean recovery of 94% administered radioactivity.

4. The predominant circulating components were identified as delafloxacin and a direct glucuronide conjugate of delafloxacin.     

Pharmacokinetics,metabolism and excretion of an inhibitor of inducible nitric oxide synthase,L-NIL-TA,in dog

1.?The pharmacokinetics, metabolism and excretion of L-NIL-TA, an inducible nitric oxide synthase inhibitor, were investigated in dog.

2.?The dose of [¹⁴C]L-NIL-TA was rapidly absorbed and distributed after oral and intravenous administration (5?mg?kg^?1), with C_max of radioactivity of 6.45–7.07?μg equivalents?g^?1 occurring at 0.33–0.39-h after dosing. After oral and intravenous administration, radioactivity levels in plasma then declined with a half-life of 63.1 and 80.6-h, respectively.

3.?Seven days after oral and intravenous administrations, 46.4 and 51.5% of the radioactive dose were recovered in urine, 4.59 and 2.75% were recovered in faeces, and 22.4 and 22.4% were recovered in expired air, respectively. The large percentages of radioactive dose recovered in urine and expired air indicate that [¹⁴C]L-NIL-TA was well absorbed in dogs and the radioactive dose was cleared mainly through renal elimination. The mean total recovery of radioactivity over 7 days was approximately 80%.

4.?Biotransformation of L-NIL-TA occurred primarily by hydrolysis of the 5-aminotetrazole group to form the active drug L-N6-(1-iminoethyl)lysine (NIL or M3), which was further oxidized to the 2-keto acid (M5), the 2-hydroxyl acid (M1), an unidentified metabolite (M2) and carbon dioxide. The major excreted products in urine were M1 and M2, representing 22.2 and 21.2% of the dose, respectively.     

Biliary excretion and enterohepatic circulation of paracetamol in the rat

1. Within 8?h after i.v. administration of paracetamol (100?mg/kg) to rats, 28.7% was excreted into bile; 1.2% dose as unchanged drug, 14.3% as the glucuronide, 8.2% as the sulphate, 4.7% as the glutathione conjugate, 0.32% as the mercapturate.

2. Rats with cannulated bile-ducts excreted 62.8% dose in the urine in 8?h compared with 83.5% in sham-operated rats. Metabolites in urine were paracetamol sulphate (63.2%), the glucuronide (12.1%), unchanged paracetamol (7%), and the mercapturate (1.2%).

3. Bile containing paracetamol and its conjugates was infused into the duodenum and within 8?h 45.3% was excreted (5.6% in bile and 39.7% in urine).

4. In rats not subjected to surgery, 91.3% dose (100?mg/kg, i.v.) was excreted in urine in 24?h. However, in rats treated twice with activated charcoal or cholestyramine (2 × 1?g/kg orally), urine excretion was decreased to 72.8 and 59.3% dose, respectively.

5. These results indicate the enterohepatic circulation of paracetamol and its metabolites in the rat.     

Identification of the metabolites of irinotecan,a new derivative of camptothecin,in rat bile and its biliary excretion

1. To investigate the metabolites and biliary excretion of new camptothecin analogue, irinotecan, the drug was administered i.v. to rats (10?mg/kg) and bile, urine and faeces were collected.

2. In rat bile, unchanged irinotecan, the metabolite 7-ethyl-10-hydroxycamptothecin (EHCPT) and unknown metabolite M-1 were found by t.l.c. and?h.p.l.c. From β-glucuronidase hydrolysis, n.m.r. spectrometry and mass spectrometry, M-1 was identified as EHCPT-glucuronide (EHCPT Glu). Other metabolites in the bile were negligible.

3. The cumulative biliary and urinary excretion of radioactivity after dosage of rats with irinotecan were 62.2% and 33.3% dose, respectively, and 9.0% of the radioactivity was excreted in the faeces.

4. Approx. 55% of the biliary radioactivity excreted in 24?h was unchanged irinotecan, 22% was EHCPT Glu, and 9% was EHCPT.

5. Approx. 18% of the biliary radioactivity was reabsorbed from the intestine.     

Studies on the different metabolic pathways of antipyrine in man: I. Oral administration of 250, 500 and 1000 mg to healthy volunteers

1 The plasma elimination rate of antipyrine, as measured by the salivary concentration decay, and the urinary excretion of antipyrine and its primary metabolites 4-hydroxy-antipyrine, norantipyrine, 3-hydroxymethyl-antipyrine and 3-carboxy-antipyrine was studied in five healthy volunteers, who received 250, 500 and 1000 mg antipyrine orally in a cross-over design.

2 The mean antipyrine half-life and metabolic clearance were 11.5 ± 2.5 h (range 10.2-16.9 h) and 3.4 ± 0.9 l/h (range 1.7-4.2 l/h) respectively after 500 mg. These values were not significantly different after 250 or 1000 mg (P > 0.1; paired t-test).

3 In 52 h urine 3.3 ± 1.2% of the dose of 500 mg antipyrine was excreted unchanged as antipyrine, 28.5 ± 2.2% as 4-hydroxy-antipyrine, 16.5 ± 6.0% as norantipyrine, 35.1 ± 7.2% as 3-hydroxymethyl-antipyrine and 3.3 ± 0.8% as 3-carboxy-antipyrine. The values obtained at the other dose levels were not significantly different (P > 0.1; paired t-test).

4 At all dose levels 4-hydroxy-antipyrine and norantipyrine were excreted in urine entirely as glucuronides. After 500 mg antipyrine, 3-hydroxymethyl-antipyrine was excreted as glucuronide to the extent of 58 ± 9% of the total excreted amount. This percentage was not significantly different at the other dose levels. 3-Carboxy-antipyrine was excreted in the free form at all three dose levels.

5 From 12 h of drug intake onwards, the urinary excretion rate curves of antipyrine and all its metabolites declined mono-exponentially with about the same half-life as the parent compound in saliva. The half-lives calculated from the excretion rate curves of 4-hydroxy-antipyrine, norantipyrine and 3-hydroxymethyl-antipyrine correlated significantly with the half-life of antipyrine in plasma. At all dose levels a relative delay in urinary excretion of 3-hydroxymethyl-antipyrine was observed compared to the urinary excretion of antipyrine and the other metabolites.

6 The ratios of the cumulative amounts of metabolites excreted in 24 h, were essentially the same as those measured in the 52 h samples.

     

The hepatic reductase null mouse as a model for exploring hepatic conjugation of xenobiotics: application to the metabolism of diclofenac

The distribution, metabolism, excretion and hepatic effects of diclofenac were investigated following a single oral dose of 10?mg/kg to wild type and hepatic reductase null (HRN) mice. For the HRN strain the bulk of the [(14)C]-diclofenac-related material was excreted in the urine/aqueous cagewash within 12?h of administration (~82%) with only small amounts eliminated via the faeces (~2% in 24?h). Wild type mice excreted the radiolabel more slowly with ca. 52 and 15% of the dose recovered excreted in urine and faeces, respectively, by 24?h post dose. The metabolic profiles of the HRN mice were dominated by acyl conjugation to either taurine or glucuronic acid. Wild type mice produced relatively small amounts of the acyl glucuronide. Whole Body Autoradiography (WBA) of mice sacrificed at 24?h post dose indicated increased retention of radioactivity in the livers of HRN mice compared to wild type mice. Covalent binding studies showed no differences between the two strains. Metabolism of diclofenac in HRN mice involved mainly acyl glucuronide formation and taurine amide conjugation. This mouse model may find utility in understanding the impact of reactive metabolite formation via routes that involve the production of acyl-CoA or acyl glucuronides of acidic drugs.