Pharmacokinetics of the M1-agonist talsaclidine in mouse, rat, rabbit and monkey, and extrapolation to man

1. Talsaclidine is an M1-agonist under development for the treatment of Alzheimer's disease. The aim of the study was to investigate the absorption, distribution, metabolism and excretion (ADME) of single intravenous and oral doses of [14C]-talsaclidine in mouse, rat, rabbit and monkey. Previous data in humans showed that the drug was mainly excreted into the urine as the unchanged parent drug. The hypothesis was tested if animal data of drugs, which are mainly excreted renally, could be extrapolated to human. 2. The apparent volume of distribution at steady-state (V(ss)) was comparable in all animal species (2-5 l x kg(-1)) indicating an extensive distribution of the drug into tissues. The plasma protein binding was low and comparable in all species including man (< or = 7%). Elimination in terms of clearance was rapid-to-moderate depending on the species. The total plasma clearance (Cl) decreased in the order: mouse (128 ml x min(-1) x kg(-1))> rat (73.9) > monkey (10.6). Urinary excretion is the dominant route of excretion (> or = 86%). 3. A good correlation was achieved with human and animal data in allometric scaling of CI and V(ss). This confirms the hypothesis that renal filtration is scalable over the species and, given a comparable protein binding, animal data is predictive for man.     

Comparative metabolism of the designer drug 4-methylthioamphetamine by hepatocytes from man,monkey, dog,rabbit, rat and mouse

Several cases of death associated with 4-methylthioamphetamine (4-MTA) have raised public concern about the abuse of this designer drug that is usually sold as Ecstasy or Flatliners. Since only very little is known about the metabolism of 4-MTA in humans we performed an in vitro study incubating racemic 4-MTA with primary hepatocytes isolated from three male human donors. Additionally, hepatocytes from male monkey (Cynomolgus), dog (Beagle), rabbit (Chinchilla), rat (Sprague-Dawley), and mouse (CD1) were examined for the metabolism of racemic 4-MTA. We observed that 4-MTA was not extensively metabolised by hepatocytes from all species examined. The main metabolite was identified as 4-methylthiobenzoic acid which, for the first time has been described as a human metabolite. In addition to metabolism we also examined 4-MTA-induced toxicity as evidenced by the ATP cellular content. Interestingly, one of the three human donors showed a dramatically increased sensitivity to the reduction in ATP content induced by 4-MTA. Comparing the species examined, the most extensive formation of 4-methylthiobenzoic acid was observed in the rabbit hepatocytes followed by human, monkey, dog and mouse hepatocytes, whereas no formation of 4-methylthiobenzoic acid was seen in the rat hepatocytes. Toxicity data suggest that rabbit hepatocytes are more resistant to 4-MTA than the other species, which may be due to the more extensive metabolism. In conclusion, we have shown that 4-methylthiobenzoic acid is the main metabolite formed from 4-MTA by human hepatocytes and also by the hepatocytes of the other tested species except the rat. Toxicity data suggest only moderate interspecies differences.     

Pharmacokinetics and metabolism of sildenafil in mouse, rat, rabbit, dog and man

1. Pharmacokinetics were studied in mouse, rat, rabbit, dog and man after single intravenous and/or oral doses of sildenafil or [14C]-sildenafil (Viagra). 2. In man, absorption from the gastrointestinal tract was essentially complete. With the exception of male rat, Tmax occurred at approximately 1 h or less. Bioavailability was attenuated by pre-systemic hepatic metabolism in all species. 3. The volume of distribution was similar in rodents and humans (1-2 l/kg) but was greater in dog (5.2 l/kg), due to lower plasma protein binding (84 versus 94-96% respectively). 4. High clearance was the principal determinant of short elimination half-lives in rodents (0.4-1.3 h), whereas moderate clearance in dog and man resulted in longer half-lives (6.1 and 3.7 h respectively). Clearances were in agreement with in vitro metabolism rates by liver microsomes from the various species. 5. After single oral or intravenous doses of [14C]-sildenafil, the majority of radioactivity was excreted in the faeces of all species. No unchanged drug was detected in the excreta of man. 6. Five principal pathways of metabolism in all species were piperazine N-demethylation, pyrazole N-demethylation, loss of a two-carbon fragment from the piperazine ring (N,N'-deethylation), oxidation of the piperazine ring and aliphatic hydroxylation. Additional metabolites arose through combinations of these pathways. 7. Sildenafil was the major component detected in human plasma. Following oral doses, AUC(infinity) for the piperazine N-desmethyl and piperazine N,N'-desethyl metabolites were 55 and 27% that of parent compound respectively.     

Metabolism of a 14C/3H-labeled GABAA receptor partial agonist in rat, dog and human liver microsomes: evaluation of a dual-radiolabel strategy

The metabolism of 2-{[2-(3-fluoropyrid-2-yl)-1H-imidazol-1-yl]methyl}-1-propyl-5-cyano-1H-benzimidazole (1), a potent subtype-selective GABA(A) receptor partial agonist, was investigated in rat, dog and human liver microsomes. Due to its significant metabolic cleavage at C(8) observed in preliminary biotransformation studies with non-radiolabeled 1, both [(14)C]1 and [(3)H]1 were synthesized with respective radioisotopes placed on either side of C(8) to determine if all microsomal metabolites formed after C(8)N-dealkylation of 1 (or its core-intact metabolites) could be detected and quantified adequately. Both radiolabeled forms of 1, used separately in mono-radiolabel studies in cross-species microsomes and concomitantly in dual-radiolabel studies in rat microsomes, permitted the detection and quantification of all metabolites of 1, and a combination of radioactive and mass spectral data allowed structural elucidation of its Phase I metabolites. As expected, the sum of (14)C-only metabolites equaled that of (3)H-only metabolites in all incubations. In-line radiometric analysis worked extremely well (and was very reproducible) for quantifying either (14)C- or (3)H-compounds within separate incubations when using mono-radiolabeled 1. However, although the in-line radiodetector provided a comprehensive qualitative metabolic profile using dual-radiolabled 1, its inability to exclude completely (14)C- from (3)H-generated counts caused a degree of ambiguity pertaining to metabolite quantification. Thus, off-line liquid scintillation counting of collected dual-radiolabeled incubation LC-fractions was employed to quantify both (14)C- and (3)H-metabolites simultaneously, while in-line radiodetection was only used for qualitative analyses accompanying MS and MS/MS experiments. These studies demonstrated the analytical feasibility of using a dual-radiolabel approach for subsequent in vivo ADME studies with 1.     

Pharmacokinetics,distribution, and disposition of esaxerenone,a novel,highly potent and selective non-steroidal mineralocorticoid receptor antagonist,in rats and monkeys

1.?Esaxerenone (CS-3150) is a novel non-steroidal mineralocorticoid receptor antagonist. The pharmacokinetics, tissue distribution, excretion, and metabolism of esaxerenone were evaluated in rats and monkeys.

2.?Following intravenous dosing of esaxerenone at 0.1–3?mg/kg, the total body clearance and the volume of distribution were 3.53–6.69?mL/min/kg and 1.47–2.49?L/kg, respectively, in rats, and 2.79–3.69?mL/min/kg and 1.34–1.54?L/kg, respectively, in monkeys. The absolute oral bioavailability was 61.0–127% in rats and 63.7–73.8% in monkeys.

3.?After oral administration of [¹⁴C]esaxerenone, the radioactivity was distributed widely to tissues, with the exception of a low distribution to the central nervous system. Both in rats and in monkeys, following oral administration of [¹⁴C]esaxerenone the main excretion route of the radioactivity was feces.

4.?Five initial metabolic pathways in rats and monkeys were proposed to be N-dealkylation, carboxylation, hydroxymethylation, O-glucuronidation, and O-sulfation. The oxidized metabolism was predominant in rats, while both oxidation and glucuronidation were predominant in monkeys.     

Pharmacokinetics of spironolactone in man

Summary Five healthy male volunteers received 500 mg Aldactone^® orally together with 100 Ci ³H-20-21-spironolactone; one elderly patient received 1 mCi ³H-spironolactone without additional cold drug. For 6 days the disposition kinetics of the drug were studied in plasma, urine and feces. The tritium concentrations in plasma reached a peak between 25–40 min after administration amounting to 2–3% of the dose/1. Up to the 12th h, they fell rapidly and showed a monoexponential decline (t _1/2 : 2.57±0.27 days) between the 36th and 96th h. Later, a striking increase in the speed of elimination of radioactivity from plasma (t _1/2 : 1.66±0.21 days) was observed. The biological half-life of labeled material in plasma was longer than that of fluorigenic compounds. 47–57% of the dose were excreted in urine and the remaining amount culd be detected in feces (total recovery 90%). The half-life of the urinary excretion rate was distinctly shorter (t _1/2 : 0.9±0.11 days) than that of total radioactivity in plasma. This, together with an observed increase of the polar fraction in urine from 35 up to 85%, which was accompanied by a decrease in plasma from 55 to 35%, suggests either tubular reabsorption or enterohepatic recirculation of lipophilic compounds. TLC-separation of the lipophilic fraction in urine revealed two previously unknown compounds of which the main congener was identified as 3-(3-oxo-7-methylsulfonyl-6, 17-dihydroxy-4-androsten-17-yl) propionic acid -lactone, as well as canrenone and the metabolites which have already been described (Karim and Brown, 1972; Karim et al., 1975). This metabolite represents the main lipophilic degradation product in urine within the first hours, whereas the 6-OH-7-methylsulfinylspirolactone leveled off and seemed to be an endexcretion product. For further characterisation, the polar fraction was subjected to acidic hydrolysis. The known metabolic pathways of spironolactone degradation are discussed.The paper includes parts of the thesis of G. Luszpinski     

Cytotoxicity of mebendazole against established cell lines from the human,rat, and mouse liver

The direct cytotoxicity of mebendazole (MBZ) was investigated by using cell lines derived from human, mouse and rat liver. It was demonstrated that Chang liver cells (derived from human liver) were more sensitive to the cytotoxic effects of MBZ than the other two cell lines. Longer incubation of the cells with MBZ resulted in stronger toxicity, and the cytotoxicity was dependent on the MBZ concentration above a certain threshold value (0.25–0.50 mg/l in a 42-h culture). Inhibition of the proliferation of Chang liver cells by MBZ was detected at a concentration of 0.008 mg/l, a lower concentration than that having a cytotoxic effect. The other two cell lines were less sensitive to the inhibitory effect of MBZ. Proliferation of human mononuclear cells following stimulation by phytohemagglutinin (PHA) was inhibited by MBZ, and this inhibition was more extensive than that of cells stimulated with whole formalin-treatedPseudomonas aeruginosa. It is suggested that dividing cells may be more sensitive to MBZ cytotoxicity. This anti-proliferative effect may be related to its clinically known side effects, such as hepatotoxicity and bone marrow suppression.     

Pharmacokinetics of fenbufen in man

Summary The pharmacokinetics of fenbufen (3.4-biphenylylcarbonyl propionic acid) a new antiinflammatory agent, and its metabolites, -hydroxy-4-biphenylbutyric acid and 4-biphenylacetic acid have been studied after oral administration to seven patients with rheumatoid arthritis. Fenbufen was administered as a single oral dose of 600 mg in hard gelatine capsules. A specific, sensitive gas chromatographic method was used to measure the concentration of the three compounds. A linear two-compartment open model appeared suitable to describe the course of the plasma level of fenbufen with time. This compound appeared in the blood after a lag time of 0.45 h and the peak plasma concentration of 5.97 µg/ml was observed after 1.19 h. The half-life of plasma disappearance was 10.26 h for fenbufen and 10.07 h and at 9.95 h for metabolites II and III, respectively.     

Evaluation of simple in vitro to in vivo extrapolation approaches for environmental compounds

As part of an effort to support in silico/in vitro based risk assessment, we evaluated the accuracy associated with conducting simple in vitro to in vivo extrapolation (IVIVE) for environmental compounds using available in vitro human metabolism data. The IVIVE approach was applied to a number of compounds with a wide range of properties spanning the diversity of characteristics of environmental compounds, and where possible the resulting estimates of the in vivo steady-state blood concentration were compared with estimates derived on the basis of human in vivo kinetic data. There appears to be a systematic bias in the estimation of intrinsic clearance (Clint) from in vitro versus in vivo data, with in vitro based estimates underestimating in vivo clearance for small values of Clint but with the opposite relationship at large values of Clint. Nevertheless, the resulting estimates of C_ss were in good agreement. The chief drawback of the simple approach used in this study, which performs the IVIVE prediction for the parent compound only, is that it is not applicable for toxicity associated with a metabolite.     

Pharmacokinetics and metabolism of dofetilide in mouse, rat, dog and man.

1. Pharmacokinetics of dofetilide were studied in man, dog, rat and mouse after single i.v. and oral doses of dofetilide or 14C-dofetilide. 2. Dofetilide was absorbed completely in all species. Low metabolic clearance in man resulted in complete bioavailability following oral administration. Higher metabolic clearance in rodents, and to a lesser extent dogs, resulted in decreased bioavailability because of first-pass metabolism. 3. Following i.v. administration, the volume of distribution showed only moderate variation in all species (2.8-6.3 l/kg). High plasma clearance in rodents resulted in short half-life values (mouse 0.32, male rat 0.5 and female rat 1.2 h), whilst lower clearance in dog and man gave longer terminal elimination half-lives (4.6 and 7.6 h respectively). 4. After single i.v. doses of 14C-dofetilide, unchanged drug was the major component excreted in urine of all species with several metabolites also present. 5. Metabolites identified in urine from all species were formed by N-oxidation or N-dealkylation of the tertiary nitrogen atom of dofetilide. 6. After oral and i.v. administration of 14C-dofetilide to man, parent compound was the only detectable component present in plasma and represented 75% of plasma radioactivity. No single metabolite accounted for greater than 5% of plasma radioactivity.     

Pharmacokinetics of the anxiolytic beta-carboline derivative abecarnil in the mouse, rat, rabbit, dog, cynomolgus monkey and baboon. Studies on species differences

The pharmacokinetics of abecarnil (isopropyl 6-(benzyloxy)-4-(methoxymethyl)-9H-pyrido [3,4-b] indole-3-carboxylate, ZK 112 119) were studied in the mouse, rat, rabbit, dog, cynomolgus monkey and baboon using 14C-labeled drug and HPLC with fluorescence detection for measurement of unchanged drug. Abecarnil was rapidly and completely absorbed after oral doses of 10 mg/kg. At higher doses, absorption was prolonged and incomplete in the cynomolgus monkey. The bioavailability of abecarnil was 20-30% in all the species investigated. The terminal half-life of the unchanged drug in plasma was relatively similar in all species (0.6-1.7 h). Abecarnil was able to pass the blood-brain barrier achieving concentrations in the brain similar to those in plasma. Tissue distribution of labeled compounds was rapid with highest concentrations in the liver, adrenals, kidneys and pancreas followed by the bone marrow, lungs, heart, fat, spleen, ovaries and thyroid gland. Excretion of radiolabeled compounds proceeded predominantly in the feces of the rat, the rabbit and the cynomolgus monkey.     

Pharmacokinetics of fentanyl in man and the rabbit

Summary Plasma levels and urinary excretion of³H-fentanyl were studied in 5 human subjects after intravenous injection of this drug. After an initial rapid decline, the plasma level of fentanyl decreased slowly and approximately exponentially. The plasma concentration of metabolites remained almost steady from 1–3 h after injection. More than 60% of the administered radioactivity was excreted through the kidneys within 4 days. Only a small proportion of it was unchanged fentanyl. The rates of fall of plasma concentration and of urinary excretion were slower in man than in rabbits. — The time courses of plasma concentrations and of urinary excretion were simulated on an analogue computer. The results support the assumption that the different time courses of concentrations in man and rabbits are caused by slower metabolism in man. It seems likely that redistribution plays a dominant part in the short duration of action of fentanyl in man.     

Pharmacokinetics of nisoldipine. III. Biotransformation of nisoldipine in rat, dog, monkey, and man

After intraduodenal administration of 14C-labelled (+/-) 3-isobutyl-5-methyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-pyridine-3,5-dicarboxylate (nisoldipine, Bay k 5552) to rats approx. 68% of the dose was excreted in the bile in the first 6 h. In an isolated perfused rat liver model the excretion with the bile was 56% of the total dose within 3 h. The recovery of radioactivity from orally administered [14C] nisoldipine was approx. 32% (rat), 23% (dog), 73% (monkey) and 74% (man), resp., in the urine. The unchanged drug was neither detected in the urine nor in the bile, but nisoldipine was present in plasma of the rat 30 min after dosing and up to 24 h in man. The drug was extensively metabolized: 18 biotransformation products were identified by comparison with synthetic reference compounds using combined GC-MS, 1 NMR-spectroscopy, mass spectrometry, gas chromatography/radio-gas chromatography and two-dimensional thin layer chromatography, 6 of them being quantitatively important (about 80% of the radioactivity excreted in urine). The metabolites identified accounted for approx. 82% (rat: bile and urine), 19% (dog, due to the low renal excretion), 58% (monkey: urine) and 64% (man: urine) of the excreted dose, resp. The following biotransformation steps occurred: hydroxylation of the isobutyl moiety, dehydrogenation of the 1,4-dihydropyridine system, oxidative ester cleavage, hydroxylation of one of the methyl groups in 2- or 6-position and subsequent oxidation to the carboxylic acid, oxidation of one of the methyl groups of the isobutyl moiety to the carboxyl group reduction of the aromatic nitro group (minor biotransformation reaction) and glucuronidation as phase II reaction.     

Metabolism and clearance of proxicromil--studies in rat, hamster, rabbit, dog, squirrel monkey, cynomolgus monkey, baboon and man

Proxicromil was extensively metabolized and eliminated as metabolites in urine and faeces by the rat, hamster, rabbit, squirrel monkey, cynomolgus monkey, baboon and man after oral administration. The pathway of metabolism in these species was by hydroxylation of the alicyclic ring principally to yield monohydroxylated metabolites with trace amounts of a dihydroxylated product. Elimination of proxicromil by the dog, however, was essentially as the unchanged drug. The lack of metabolism of the drug by the dog resulted in the dog having a dependence on biliary excretion of the unchanged drug for clearance. These differences in clearance routes between species were reflected in the plasma clearance of the drug. The value for rat, a species capable of metabolism, was approximately 20 fold (4.1 ml min-1 kg-1) greater than the corresponding value for dog (0.2 ml min-1 kg-1). Inhibiting the metabolism of proxicromil in the rat with SKF-525A lowered plasma clearance of proxicromil (0.6 ml min-1 kg-1) and elevated the proportion of unchanged drug cleared by biliary excretion.     

Biotransformation of zeranol: disposition and metabolism in the female rat, rabbit, dog, monkey and man

The disposition of [3H]zeranol has been studied in the female Wistar rat, New Zealand rabbit, beagle dog, rhesus monkey and man. The blood elimination half-life of total radioactivity in rabbit was 26 h, monkey 18 h and man 22 h. In all species studied the drug was absorbed, oxidized and/or conjugated, and was extensively excreted via the bile in all species except rabbit and man, in which urinary excretion predominated. Blood total radioactivity in man probably consisted entirely of conjugates of zeranol and/or its metabolites. Urinary metabolites in all species included conjugates (beta-glucuronides and/or sulphates) of zeranol and the major metabolite zearalanone. A more polar minor metabolite was isolated from human urine and was shown to be hydroxy-zeranol. Taleranol (7 beta-zearalanol, the lower-melting diastereoisomer), a probable metabolite of zeranol (7 alpha-zearalanol, the higher-melting diastereoisomer) in animals and in man, was shown to be a urinary metabolite in a female New Zealand white rabbit which had received [3H]zeranol (8 mg/kg per day) for seven days. A reverse isotope dilution method was developed for the quantification of both diastereoisomers of zearalanol, and also zearalanone, in urine.     

Metabolites of isocorynoxeine in rats after its oral administration

This work presents the metabolites of isocorynoxeine (ICOR), which is one of four bioactive tetracyclic oxindole alkaloids isolated from Uncaria hooks used commonly in the traditional Chinese medicines and Kampo medicines. After oral administration of 40 mg kg^? 1 ICOR to rats, bile was drained and analyzed by LC-MS. Two phase I metabolites, namely 11-hydroxyisocorynoxeine (M1) and 10-hydroxyisocorynoxeine (M2), and two phase II metabolites, namely 11-hydroxyisocorynoxeine 11-O-β-d-glucuronide (M3) and 10-hydroxyisocorynoxeine 10-O-β-d-glucuronide (M4), were isolated from rat excreta and bile, respectively, whose structures were elucidated on the basis of CD, NMR, and MS.     

Pharmacokinetics of iododoxorubicin in the rat, dog, and monkey.

The pharmacokinetics of iododoxorubicin (I-DOX) have been studied after single dose administration in the rat (iv and po), dog (iv and po), and monkey (iv). Plasma levels and amounts in urine were monitored by HPLC for both I-DOX and its biologically active metabolite, iododoxorubicinol (I-DOXOL). Plasma levels of I-DOX after iv administration could be described by a three-exponential curve with extremely fast initial phase. Terminal elimination half-lives of I-DOX were similar, 6-7 hr, in all three species. Body weight-normalized clearance (CL) and distribution volumes (Vd) of I-DOX were lower in the dog, but were similar in rat and monkey. The pharmacokinetic parameters also implied metabolic differences between species. Mean I-DOXOL/I-DOX AUC ratios were 0.02, 0.47, and 0.58, respectively, in rat, dog, and monkey, values considerably lower than reported in human studies. I-DOXOL remained slightly longer in the body than I-DOX, as seen both from terminal half-lives (9-11 hr) and mean residence times. In all species, renal excretion was virtually negligible: the amount of I-DOX + I-DOXOL in urine was less than 2% of dose. Mean bioavailabilities of I-DOX were 0.23 and 0.46 in rat and dog, respectively, and, in the latter, about half of I-DOXOL formation occurred during or before the first pass.     

Pharmacokinetics of a novel surface-active agent,purified poloxamer 188, in rat,rabbit, dog and man

Purified poloxamer 188 (PP188) is a non-ionic, block copolymer surfactant that is currently being evaluated clinically in sickle cell disease vaso-occlusive crisis and acute chest syndrome and preclinically in spinal cord injury and muscular dystrophy. This paper describes the pharmacokinetics of PP188 in rats, pregnant rats, pregnant rabbits, dogs and humans. Plasma protein binding interaction studies demonstrated no clinically significant effects on narcotic analgesics, hydroxyurea, warfarin, diazepam or digitoxin, but an increase in free fraction for propranolol. The plasma concentrations increased proportionate with increasing dose in all species tested. Renal clearance accounted for 90% of total plasma clearance in man. A single metabolite was detected and quantified in the plasma from dogs and humans that was cleared more slowly than parent drug. Allometric scaling of plasma clearance and volume of distribution at steady-state (Vss) across species provided good predictions of the pharmacokinetic parameters in humans. Based on the comparative pharmacokinetics of PP188 in rat, rabbit, dog and man, all three animal species were appropriate models for evaluating various aspects of PP188's toxicological profile.