Metabolic disposition of enciprazine,a non-benzodiazepine anxiolytic drug,in rat,dog and man

1. The excretion and metabolism of enciprazine, an anxiolytic drug, was examined in rat, dog and man.

2. In rats and dogs that received ¹⁴C-enciprazine dihydrochloride orally and by i.v. injection, the drug was well absorbed. Radioactivity was excreted predominantly in the faeces of rats, equally in urine and faeces of dogs, and to a major extent in human urine.

3. Metabolic profiles, which were evaluated in urine and in rat bile, were similar following oral and i.v. dosing to rats and dogs.

4. Unchanged drug was not detected in rat, dog or human excreta. Glucuronide conjugates of 4-hydroxyenciprazine, m-desmethylenciprazine, p-desmethylenciprazine and enciprazine were detected in the excreta of all three species. A glycol metabolite was present only in rat bile and human urine. A metabolite desmethylated in the phenyl ring of the phenylpiperazine moiety also appeared to be present only in human urine.

5. Structural confirmation of the major metabolites in human urine and rat bile was accomplished by?h.p.l.c.-mass spectrometry.     

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.     

Biotransformation of sultopride in man and several animal species

1. The biotransformation of sultopride has been investigated in rat, rabbit, dog and man.

2. In man sultopride was metabolically stable, and about 90% of an oral dose was excreted in urine unchanged and 4% as oxo-sultopride.

3. Rat, rabbit and dog metabolized sultopride more extensively and excreted less than 40% of an oral dose of ¹⁴C-sultopride in urine.

4. Four similar metabolites were excreted by the three animal species but the relative portions differed. The major radioactive component in rat urine was O-desmethyl sultopride, whereas oxo-sultopride and O-desmethyl sultopride were the major urinary metabolites in rabbit. Dog formed N-desethyl sultopride and oxo-sultopride as major urinary metabolites.

5. The male rat excreted smaller amounts of unchanged sultopride in urine than did the female rat.

6. The unchanged sultopride excreted in rat urine was increased slightly by repeated administration.     

Metabolism and disposition of 2,2',4,4',5-pentabromodiphenyl ether (BDE99) following a single or repeated administration to rats or mice

The metabolism and disposition of 14C-labelled 2,2',4,4',5-pentabromodiphenyl ether (BDE99) were studied in F344 rats and B6C3F1 mice. Approximately 85% of a 1 micromol kg-1 oral dose was absorbed by male rats and mice. Within 24 h following oral doses ranging from 0.1 to 1000 micromol kg-1 to rats, 39-47% of the dose was excreted in the faeces (including 16% unabsorbed), up to 2% was excreted in the urine, and 34-38% remained in the tissues, mostly in adipose tissue. Mice excreted more in the urine and less in the faeces than rats. Tissue accumulation was observed following repeated dosing to rats. Two dihydrohydroxy-S-glutathionyl and two S-glutathionyl conjugates of BDE99, 2,4,5-tribromophenol glucuronide, two mono-hydroxylated BDE99 glucuronides, and three mono-hydroxylated tetrabromodiphenyl ether glucuronides were identified in male rat bile. 2,4,5-Tribromophenol and its glucuronide and sulfate conjugates, were identified in male rat urine. 2,4,5-Tribromophenol, one mono-hydroxylated tetrabromodiphenyl ether, and two mono-hydroxylated BDE99 were characterized in male rat faeces. BDE99 undergoes more extensive metabolism than does BDE47. Half of the absorbed oral dose in male rats was excreted in 10 days mostly as metabolites derived from arene oxide intermediates.     

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.     

The biotransformation of [14C]minaprine in man and five animal species

1. [¹⁴C]Minaprine was administered as a single oral dose to five animal species and to a healthy and informed volunteer. Excretion of radioactivity was followed during 48?h in urine and faeces; biliary excretion was followed only in rat.

2. Urinary metabolites were isolated and identified by mass spectrometry.

3. A quantitative comparison of metabolites in different species was made. On the basis of these data it is concluded that the dog is not a suitable model for man for pharmacological or toxicological studies.

4. The major metabolic route is 4-hydroxylation of the aromatic ring. The only unexpected metabolic route found was the biotransformation of the morpholino ring, probably by reductive ring-cleavage.

5. About 50% of the ¹⁴C was excreted in 0-48?h urine. The other 50% was excreted in the 0-48?h faeces. In the rat, this was attributed entirely to biliary excretion. The drug is well absorbed after oral administration and is not accumulated in the body.     

Disposition and urinary metabolic pattern of cabergoline,a potent dopaminergic agonist,in rat,monkey and man

1. The disposition and urinary metabolic pattern of ¹⁴C-cabergoline was studied in rat, monkey and man after oral administration of the labelled drug.

2. In all species radioactivity was mainly excreted in faeces, with urinary excretion accounting for 11, 13 and 22% of the dose in rat, monkey and man, respectively.

3. After oral treatment, biliary excretion of radioactivity in rat accounted for 19% of the dose within 24?h.

4. Unchanged drug in 0-24-h urine samples of rat, monkey and man amounted to 20, 9 and 10% of urinary radioactivity, respectively. In the 24-72-h urine samples of all species the relative percentage of unchanged drug increased compared with that measured in the 0-24-h urine.

5. The main metabolite was the acid derivative (FCE21589), which in 0-24-h urine samples of rat, monkey and man accounted for 30, 21 and 41% of urinary radioactivity, respectively.

6. Other metabolites identified in urine of all species resulted from hydrolysis of the urea moiety, the loss of the 3-dimethylaminopropyl group and the deallylation of the piperidine nitrogen.     

The biotransformation of [14C]lormetazepam in dogs,rabbits, rats and rhesus monkeys

1. After oral or intravenous doses (0.25?mg/kg) of [¹⁴C]lormetazepam to rats, most of the urinary radioactivity was associated with polar components and < 1% dose was excreted as unconjugated lormetazepam. About 30% of an oral dose was excreted in rat bile as a conjugate of lormetazepam and about 50% dose as polar metabolites. Plasma also contained mainly polar metabolites, and unchanged lormetazepam represented at most 10% of total plasma radioactivity after an oral dose.

2. Almost all the radioactivity in dog, rhesus monkey and rabbit urine, after oral or intravenous doses (0.5–0.7?mg/kg) of [¹⁴C]lormetazepam, was associated with conjugated material. In the dog there were only two major components, conjugates of lormetazepam and lorazepam (N-desmethyl-lormetazepam) which accounted for about 24% and 14% respectively of the oral dose in the 0–24?h urine. The same two conjugated components were also present in dog bile. Conjugated lormetazepam was the only major component in monkey and rabbit urine and accounted for about 60% dose in the 0–24?h urine of each species, while conjugated lorazepam accounted for only about 0.5% and 4% respectively.

3. Dog and monkey plasma contained mostly conjugated material after oral and intravenous doses (0.05–0.07?mg/kg of [¹⁴C]lormetazepam. Dog plasma after an oral dose contained conjugates of both lormetazepam and lorazepam with peak concn. at 1?h of 130 and 47 ng/ml respectively. Concn. of these conjugates in plasma declined with apparent terminal half-lives of about 17 and 27?h respectively after oral doses, and 13?h in both cases after intravenous doses. Conjugated lormetazepam was the only major component in monkey plasma representing a peak concn. of 180 ng/ml at 1?h after an oral dose, and declined with an apparent terminal half-life of about 11?h after oral or intravenous doses.

4. Lormetazepam crosses the placental ‘barrier’ of rabbits: its concn. in the foetus were similar to those in maternal plasma after intravenous doses.     

The disposition of [14C]-labelled benazepril HC1 in normal adult volunteers after single and repeated oral dose

1. The disposition of [¹⁴C]-labelled benazepril HC1, an ACE-inhibitor, was studied in four normal adult volunteers after a single oral dose of 20 mg and after repeated doses of 20 mg once daily for 5 days. Radioactivity was measured in plasma, urine and faeces. The prodrug ester benazepril and the pharmacologically active metabolite benazeprilat were determined quantitatively in plasma and urine by a g.c.-m.s. method. The pattern of metabolites in urine was analysed semiquantitatively by h.p.l.c.-radiometry.

2. After a single oral dose at least 37% was absorbed, as indicated by urinary recovery. The peak plasma concentration of benazepril (0.58. 0.13 nmol/g (SD)) was observed at 0.5 h after dose, indicating rapid absorption. Peak concentrations of radioactivity (1.88.0.48 nmol/g) and of active benazeprilat (0.84. 0.25 nmol/g) were observed at 1 h after dose, demonstrating rapid bioactivation.

3. The area under the plasma curve (AUC_0-96h) of total radioactivity amounted to 9.7. 1.1 (nmol/g) h, 5% of which was accounted for by benazepril and about 50% by benazeprilat.

4. Over 9 days 96.8. 0.5% of the dose was excreted in urine and faeces. Urinary excretion accounted for 37.0. 6.0% of the dose, 80% of which was recovered in the first 8 h after dosing.

5. In urine, only 0.4% of the dose (1% of the radioactivity) was excreted as unchanged benazepril, indicating that the compound was extensively metabolized. Benazeprilat accounted for 17% of the dose (about half of the radioactivity; 0-96 h). Glucuronide conjugates of benazepril and benazeprilat constituting approximately 11% and 22% of the radioactivity (about 4% and 8% of the dose; 0-48 h) were tentatively identified.

6. Repeated oral treatment with benazepril HC1 did not influence the pharmacologically relevant kinetics and disposition parameters.     

Excretion and Biotransformation of Carboxymethyl-cysteine in Rat,Dog, Monkey and Man

1. Following an oral dose of S-carboxymethyl[³⁵S]cysteine, monkey (rhesus and African green), rat, dog, and man excreted 77, 88, 95, and 100% respectively of the ³⁵S radioactivity in urine and 7·0, 2·5, 0·7, and 0·3% in faeces during a 3 to 4 day period.

2. The principal drug-related components excreted were unchanged carboxymethylcysteine, dicarboxymethyl sulphide and inorganic sulphate.

3. Rat, dog, and man excreted primarily dicarboxymethyl sulphide and unchanged carboxymethylcysteine and no inorganic sulphate (rat, 7%).

4. Monkey excreted largely inorganic sulphate, moderate amounts of dicarboxymethyl sulphide and a trace of unchanged drug.     

Kinetics and disposition of picumeterol in animals

1. The pharmacokinetics and disposition of picumeterol, a novel β₂ receptor agonist agent, have been studied in the rat and dog following administration by inhalation, intravenous and oral routes at various dose levels.

2. Picumeterol was found to be transferred across the lung of the rat and dog following inhalation dosage. After i.v. dosage picumeterol was eliminated from plasma with a half-life of about 1?h in the rat and about 2?h in the dog. Plasma clearance in the rat was about twice liver blood flow and the plasma levels of picumeterol were low after oral administration.

3. Following instillation of ¹⁴C-picumeterol to the trachea of isolated respiring rat lung preparations radioactivity was transferred from the airways to perfusion media as unchanged drug within 2?min. After 2?h perfusion, no metabolites were detected in the recirculation perfusate or lung.

4. Picumeterol was extensively metabolized in vivo in the rat (about 95%) and dog (about 90%) and in vitro in microsomal preparations of rat, dog and human liver. O-dealkylation and β-oxidation are important as routes of metabolism.

5. Radioactivity was largely excreted in the urine of the rat and dog (> 50% of dose), as metabolites, following i.v. administration. There was some excretion of radioactivity in dog bile. Extensive first-pass metabolism was found after oral administration in the rat.     

Metabolic disposition of enciprazine, a non-benzodiazepine anxiolytic drug, in rat, dog and man.

1. The excretion and metabolism of enciprazine, an anxiolytic drug, was examined in rat, dog and man. 2. In rats and dogs that received 14C-enciprazine dihydrochloride orally and by i.v. injection, the drug was well absorbed. Radioactivity was excreted predominantly in the faeces of rats, equally in urine and faeces of dogs, and to a major extent in human urine. 3. Metabolic profiles, which were evaluated in urine and in rat bile, were similar following oral and i.v. dosing to rats and dogs. 4. Unchanged drug was not detected in rat, dog or human excreta. Glucuronide conjugates of 4-hydroxyenciprazine, m-desmethylenciprazine, p-desmethylenciprazine and enciprazine were detected in the excreta of all three species. A glycol metabolite was present only in rat bile and human urine. A metabolite desmethylated in the phenyl ring of the phenylpiperazine moiety also appeared to be present only in human urine. 5. Structural confirmation of the major metabolites in human urine and rat bile was accomplished by h.p.l.c.-mass spectrometry.     

Metabolism and kinetics of amlodipine in man

1. The disposition of amlodipine, R,S,2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-1,4-dihydropyridine has been studied in two human volunteers using single oral and intravenous doses of ¹⁴C-amlodipine. The drug was well absorbed by the oral route while the mean oral bioavailability for unchanged drug was 62˙5%.

2. Renal elimination was the major route of excretion with about 60% of the dosed radioactivity recovered in urine. Mean total recovered radioactivity in urine and faeces amounted to 84% for both the oral and intravenous routes.

3. Apart from a small amount of unchanged amlodipine (10% of urine ¹⁴C), only pyridine metabolites of amlodipine were excreted in urine. The majority (<95%) of the metabolites excreted in the 0-72h post-dose period were identified; the major metabolite was 2-([4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-pyridyl]methoxy) acetic acid and this represented 33% of urinary radioactivity. The data indicate that oxidation of amlodipine to its pyridine analogue is the principal route of metabolism with subsequent metabolism by oxidative deamination, de-esterification and aliphatic hydroxylation.

4. For the two volunteers, amlodipine concentrations in plasma declined with a mean half-life of 33 h, while slower elimination of total drug-related material from plasma was observed, consistent with prolonged excretion (up to 12 days) of metabolites in urine and faeces. Only amlodipine and pyridine metabolites were found in the circulation. As these pyridine derivatives have minimal calcium antagonist activity the efficacy of amlodipine in man can most probably be attributed to the parent drug.     

Absorption,distribution and excretion of lacidipine,a dihydropyridine calcium antagonist,in rat and dog

1. The absorption, distribution and excretion of lacidipine have been studied in rat and dog after i.v. (0.05 mg/kg for rat; 0.5 mg/kg for dog) and oral dosage (2.5 mg/kg for rat; 2.0 mg/kg for dog).

2. Lacidipine was rapidly and extensively absorbed after oral dosing, in both species. Oral bioavailability was up to 26% in rat and up to 32% in dog, due to extensive first-pass metabolism.

3. After oral administration, peak levels of radioactivity were reached at 4-8 h in rat and 1-2 h in dog. Unchanged lacidipine peaked at 1-2 h in both species. Plasma levels of radioactivity were higher in female rats than in males but there was no difference in levels of unchanged drug.

4. After i.v. dosing the terminal half-life of unchanged drug was 2.9 h in rat and 8.2 h in dog. The half-life of radioactivity in plasma was longer in both species.

5. After both routes of administration, radioactivity was rapidly distributed in rat tissues with the highest concentration in liver, fat and gastrointestinal tract. Only traces of radioactivity were detected in the CNS and in rat foetuses.

6. Extensive biliary elimination occurred, and most of the radioactivity (73-95%) was excreted in the faeces after i.v. or oral administration.

7. The compound was extensively metabolized, no significant amount of unchanged drug was excreted in bile or urine.     

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.     

Absorption,distribution, metabolism and excretion of telmesteine,amucolitic agent,in rat

1. The metabolism and disposition of telmesteine, a muco-active agent, have been investigated following single oral or intravenous administration of ¹⁴C-telmesteine in the Sprague–Dawley rat.

2. ¹⁴C-telmesteine was rapidly absorbed after oral dosing (20 and 50mg kg^-1) with an oral bioavailability of > 90% both in male and female rats. The C_max and area under the curve of the radioactivity in plasma increased proportionally to the administered dose and those values in female rats were 30% higher than in male rats.

3. Telmesteine was distributed over all organs except for brain and the tissue/plasma ratio of the radioactivity 30min after dosing was relatively low with a range of 0.1–0.8 except for excretory organs.

4. Excretion of the radioactivity was 86% of the dose in the urine and 0.6% in the faeces up to 7 days after oral administration. Biliary excretion of the radioactivity in bile duct-cannulated rats was about 3% for the first 24 h. The unchanged compound mainly accounted for the radioactivity in the urine and plasma.

5. Telmesteine was hardly metabolized in microsomal incubations. A glucuronide conjugate was detected in the urine and bile, but the amount of glucuronide was less than 6% of excreted radioactivity.     

Metabolism of 14C-thymoxamine in rat and man

1. After oral administration of ¹⁴C-thymoxamine to rat and man the total ¹⁴C excreted in urine and faeces was determined.

2. Six metabolites were isolated from the excreta of man and rat by chemical extraction and identified by g.l.c.-mass spectral analyses.

3. Two other metabolites, highly polar and resistant to enzymic hydrolysis, were isolated by extraction on XAD₂ resin and h.p.l.c. analysis. These two metabolites were identified by n.m.r. and by mass spectrometry in the fast atomic bombardment mode.

4. These two major metabolites of thymoxamine in man and rat have been identified and characterised as the sulphate conjugates of desacetyl-thymoxamine and N-monodesmethyl-desacetyl-thymoxamine.     

Biochemical studies on phthalic esters I. Elimination, distribution and metabolism of di-(2-ethylhexyl)phthalate in rats.

Elimination, distribution and metabolism of di-(2-ethylhexyl)phthalate (DEHP) were studied in the rat by the tracer technique. About 80% of the dose was excreted in the urine and faeces in 5 to 7 days following intravenous or oral administration. Excretion in the urine was generally slightly greater than that in the faeces. After intravenous administration of [14C] DEHP the radioactivity was preferentially localized in the liver for a short period. Delayed excretion of DEHP was observed in particular in adipose tissue. After oral dosing no significant retention was found in organs and tissues. Radioactivity measurements showed that affinity was lowest for testicles and brain regardless of whether [14C] DEHP was administered orally or intravenously. Orally ingested DEHP was excreted unchanged in the faeces and four major metabolites were detected in the urine.     

Absorption, distribution, metabolism and excretion of cizolirtine, a new analgesic compound, in rat and dog.

1. The pharmacokinetics of cizolirtine citrate, a new analgesic compound, were studied in the rat and dog following single oral and intravenous doses. 2. Absorption of radioactivity was fast and complete regardless of the species, and no dose and food-related differences were found. However, the elimination half-life of unchanged cizolirtine was shorter in rat than in dog. 3. Tissue distribution of total radioactivity in rat differed widely and a high affinity for liver, kidney, gastrointestinal and pigmented tissues was observed. In blood and almost all tissues the highest concentrations were reached at 20 min; beyond that time the decline of radioactivity in most tissues was parallel to that in blood. 4. The percentage of radioactivity excreted in the rat was 68% in urine and 21% in faeces, the latter being apparently due to drug enterohepatic circulation. In the dog, 92 and 4% of the radioactivity was found in urine and faeces respectively. The contribution of renal excretion to cizolirtine elimination was <5% in rat and 20% in dog. Twelve metabolites were detected in rat and six in the dog by radio-hplc analysis of urine.     

Some Applications of Mass Spectrometry in Drug Metabolism Studies

1. Bile secreted from rats given single oral doses of 2-chloro-N-isopropylacetanilide (propachlor) contained 58% dose as metabolites from the mercapturic acid pathway (glutathione, mercapturate, cysteine conjugates, and a sulphoxide of the mercapturate).

2. Bile secreted from rats given single oral doses of the cysteine conjugate of propachlor contained glucuronide conjugates of hydroxylated 2-methylsulphonyl-N-isopropylacetanilides.

3. In contrast, when the intestinal microflora were bypassed by intravenous administration of the cysteine conjugate of propachlor, the bile contained only the mercapturate and the sulphoxide of the mercapturate.

4. Rats fed an antibiotic-containing diet and given single oral doses of either propachlor or the cysteine conjugate of propachlor excreted only mercapturic acid pathway metabolites in the urine, bile, and faeces, and no methylsulphonyl-containing metabolites. Faecal ¹⁴C from the antibiotic-fed rats given either propachlor or the cysteine conjugate of propachlor was extractable, in contrast to previously reported unextractable faecal ¹⁴C residues from untreated rats given propachlor orally.

5. From these results, we conclude that metabolism by the microflora was necessary for production of the methylsulphonyl-containing metabolites excreted by the rat. Enterohepatic circulation of the xenobiotic moiety of these mercapturic acid pathway metabolites is influenced by the presence of a microbial C-S lyase.