Pharmacokinetics of the anticoagulant 14C-DX-9065a in the healthy male volunteer after a single intravenous dose.

1. The plasma pharmacokinetics, excretion and metabolism of DX-9065a were studied in the healthy male Caucasian volunteer after a single intravenous dose of 10 mg 14C-labelled DX-9065a. 2. At the end of a 1 h infusion, the mean plasma concentration of total radioactivity was 380 ng ml(-1) (equivalent to unchanged DX-9065). Thereafter, it decreased in a bi-exponential manner and was below the detection limit by 48 h after dosing. The half-life for the distribution phase was 6.93 h. 3. The total radioactivity recovered in urine and faeces by 336 h post-dose was 83.8% of the administered dose, with excretion ongoing at the end of the 14-day collection. The major route of excretion was via urine, accounting for a mean of 77.6% of the administered radioactivity. The urinary excretion profile was biphasic, consisting of rapid (0-24 h) and slow (24-336 h) phases. A large renal clearance suggested that renal tubular secretion might contribute to the excretion of DX-9065 via urine. 4. No metabolite peaks in the radio-HPLC chromatograms of urine samples were detected, indicating that biotransformation of DX-9065 does not play a significant role in the elimination of DX-9065 in man.

Pharmacokinetics and safety of ascending single doses of DZ-2640, a new oral carbapenem antibiotic, administered to healthy Japanese subjects.

DZ-2640 is the ester-type oral carbapenem prodrug of an active parent compound, DU-6681. The pharmacokinetics and safety of DU-6681 were investigated in six studies after oral administration of a single dose of DZ-2640 to healthy male Japanese volunteers at doses of 25, 50, 100, 200, and 400 mg (as the equivalents of DU-6681) in the fasted state. The same volunteers received the drug at a dose of 100 mg in the fasted and fed states to examine the effect of food intake on the bioavailability of DZ-2640. The concentrations of DU-6681 in plasma and urine were determined by a validated high-performance liquid chromatography method and a bioassay. A good correlation between both methods was seen, indicating an absence of major active metabolites. The mean maximum concentrations of DU-6681 in plasma (C(max)) ranged from 0.263 microgram/ml (25-mg dose) to 2.489 microgram/ml (400-mg dose) and were reached within 1.5 h following drug administration. After reaching the C(max), plasma DU-6681 concentrations declined in a monophasic manner, with a half-life of 0.47 to 0.89 h. The area under the concentration-time curve (AUC) and C(max) increased almost linearly with the dose up to the 200-mg dose. The AUC and C(max) increased less than proportionally after administration of the 400-mg dose, suggesting a reduction in drug absorption. The plasma protein binding of DU-6681 was in the range of 23.3 to 25.6%. The cumulative urinary recoveries (0 to 24 h) were in the range of 31.9 to 44.9%. The AUC was slightly but statistically significantly reduced by food intake. However, the C(max), half-life, and recovery in urine were not affected by food intake. The renal clearance (402 to 510 ml/min) was much greater than the mean glomerular filtration rate (ca. 120 ml/min), which indicated active tubular secretion of the drug. A mild transient and moderate diarrhea was observed in two of six volunteers in the study with a single dose of 25 mg. Mild soft stools were observed in two of six volunteers who received a 400-mg dose of the drug.

Pharmacokinetics of CPT-11 in rhesus monkeys.

PURPOSE: To examine the pharmacokinetic relationships between humans and monkeys, we studied the disposition of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), in rhesus monkeys. METHODS: CPT-11 was administered to a total of six monkeys at doses of 3, 7, 15 and 25 mg/kg by intravenous infusion for 10 min and plasma concentrations and pharmacokinetic parameters of CPT-11 determined. RESULTS: Maximum plasma concentrations at 25 mg/kg reached around 10000 ng/ml, and dropped to 500 ng/ml in 8 h. Plasma concentrations of SN-38 remained between 2 and 10 ng/ml. Mean values of systemic clearance, mean residence time and distribution volume at steady state, the major pharmacokinetic parameters for CPT-11, were 13.3 (ml/min per kg), 192 (min) and 2553 (ml/kg), respectively. The initial plasma concentration ratio of lactone to total CPT-11, 76%, declined to about 20% within 75 min, and the final ratio was about 40% at 8 h; the initial ratio of SN-38 was 72%, dropped to 34% within 70 min and finally recovered to 55% at 8 h. CONCLUSION: Comparison with human data revealed that systemic clearances of CPT-11 and the maximum AUC of SN-38 were not as different between humans and monkeys as between humans and mice, but the metabolic conversion of CPT-11 into SN-38 in monkeys was significantly lower than in humans.

Effects of pantoprazole on xenobiotic metabolizing enzymes in rat liver microsomes: a comparison with other proton pump inhibitors.

The effects of pantoprazole on xenobiotic metabolizing enzymes in rat liver microsomes were examined. Groups of female Sprague-Dawley rats were orally administered pantoprazole and other proton pump inhibitors, omeprazole and lansoprazole, at 5, 50, or 300 mg/kg/day for 7 days, followed by assays to detect changes in the levels of liver microsomal protein, cytochrome P450, cytochrome b5, NADPH cytochrome c reductase, and drug metabolizing enzyme activities. Increases in total cytochrome P450 contents were evident after a 7-day high-dose administration of all the proton pump inhibitors tested, and the increase by treatment with pantoprazole was less than that with lansoprazole. The three proton pump inhibitors increased the enzymatic activities and cytochrome P450 enzyme levels of CYP1A, CYP2B, and CYP3A. CYP1A was less induced with pantoprazole than with omeprazole or lansoprazole. In contrast, CYP2B was more strongly induced with pantoprazole than with other proton pump inhibitors. NADPH cytochrome c reductase was induced with omeprazole and pantoprazole. The present results suggest that enzyme induction differs among these proton pump inhibitors not only quantitatively but also qualitatively.

Multispecific organic anion transporter is responsible for the biliary excretion of the camptothecin derivative irinotecan and its metabolites in rats.

Irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin (CPT-11), is a potent anticancer drug that is increasingly used in chemotherapy. A frequent limiting side effect involves gastrointestinal toxicity (diarrhea), which is thought to be related to the biliary excretion of CPT-11 and its metabolites. Accordingly, the biliary excretion mechanisms for both the lactone and carboxylate forms of CPT-11 and its metabolites, SN-38 and its glucuronide (SN38-Glu), were investigated using Sprague-Dawley (SD) rats and Eisai hyperbilirubinemic rats (EHBR), with the latter being mutant rats with a genetic deficiency of the canalicular multispecific organic anion transporter. After i.v. administration of CPT-11, the biliary excretion clearance, defined as the biliary excretion rate normalized to the hepatic concentration, of both the lactone and carboxylate forms of SN38-Glu was much lower in EHBR. The biliary excretion clearance for the carboxylate form of both CPT-11 and SN-38 was also substantially smaller in EHBR and showed marked saturation with increasing dose only in SD rats. On the other hand, the biliary excretion clearance for the lactone forms of CPT-11 and SN-38 showed only a minimal difference in EHBR, compared with SD rats. These results suggest that, for the carboxylate form of CPT-11 and SN-38 and the carboxylate and lactone forms of SN38-Glu, there exists a specific transport system at the bile canalicular membrane that is deficient in EHBR. To confirm this hypothesis, the uptake of these substrates by isolated hepatic canalicular membrane vesicles (CMV) was examined. ATP-dependence was clearly observed for the uptake of these four compounds by CMV prepared from SD rats but not by CMV from EHBR. In addition, the compounds inhibited the ATP-dependent uptake of S-(2,4-dinitrophenyl) glutathione by CMV from SD rats, in a concentration-dependent manner. These results suggest that the biliary excretion of the carboxylate forms of CPT-11 and SN-38 and the carboxylate and lactone forms of SN38-Glu is mediated by the multispecific organic anion transporter, which is deficient in EHBR.

Differential stereoselective pharmacokinetics of pantoprazole, a proton pump inhibitor in extensive and poor metabolizers of pantoprazole--a preliminary study.

Pantoprazole (PAN) is a proton pump inhibitor that is administered as a racemic mixture. The pharmacokinetics of PAN enantiomers were investigated in extensive metabolizers (EMs) and apparent poor metabolizers (PMs) of PAN who received a single, 40, 60, or 80 mg oral dose of racemic PAN as enteric-coated formulation. In the EMs, the serum concentrations of (-)-PAN were slightly higher than those of (+)-PAN at each dose level. The (+)/(-) ratios for the area under the concentration-time curve (AUC) and the half-life were 0.58-0.89 and 0.62-0.88, respectively. In the PMs, the serum concentrations and both enantiomers were much higher than those in the EMs at each dose level and significant differences in pharmacokinetics of (+)- and (-)-PAN were observed. The half-lives for (+)-PAN were 2.67-3.77 times longer than those for (-)-PAN. The AUCs for (+)-PAN were 2.65-3.45 times greater than those for (-)-PAN. Therefore, the metabolism of (+)-PAN is impaired to a greater extent than (-)-PAN in the PMs, which resulted in the stereoselective disposition of PAN in the PMs. It has been suggested that the EMs and the PMs of PAN could be differentiated by determining the (+)/(-) enantiomer ratio in serum at one time point, possibly 2-6 h after oral dosing, because the (+)/(-) enantiomer ratios in the PMs were opposite those in the EM subjects.

Metabolic disposition of pantoprazole, a proton pump inhibitor, in relation to S-mephenytoin 4'-hydroxylation phenotype and genotype.

OBJECTIVES: To assess the possible relationship between the metabolic disposition of pantoprazole and genetically determined S-mephenytoin 4'-hydroxylation phenotype and genotype. METHODS: The pharmacokinetic disposition of pantoprazole was investigated in 14 Japanese male volunteers (seven extensive and seven poor metabolizers of S-mephenytoin). All subjects received a single 40 mg oral dose of pantoprazole as the enteric-coated formulation. RESULTS: An interphenotypic difference in the metabolic disposition of pantoprazole was observed: the mean values for area under the concentration-time curve (AUC), elimination half-life (t1/2), and apparent oral clearance were significantly (p < 0.01) greater, longer, and lower, respectively, in the poor metabolizers than in the extensive metabolizers. The mean AUC of pantoprazole sulfone was greater (p < 0.01) in the poor metabolizers than in the extensive metabolizers, whereas the mean AUC of the main demethylated metabolite (M2) was lower (p < 0.01) in the poor metabolizers than in the extensive metabolizers. A significant negative correlation was observed between the individual values for log10% urinary excretion of 4'-hydroxymephenytoin and AUC of pantoprazole (rs = -0.816; p < 0.005). The CYP2C19 genotyping test results were found to be in a complete accordance with the phenotypes. CONCLUSION: These data indicated that the metabolic disposition of pantoprazole is under the pharmacogenetic control of S-mephenytoin 4'-hydroxylase (CYP2C19).

Effects of proton pump inhibitors on thyroid hormone metabolism in rats: a comparison of UDP-glucuronyltransferase induction.

The effects of proton pump inhibitors on thyroid hormone metabolism in rats were examined. Pantoprazole, omeprazole, and lansoprazole were administered repeatedly to female SD rats at doses of 5, 50, and 300 mg/kg/day for 1 week, and changes in UDP-glucuronyltransferase activities were examined. Increases in o-aminophenol UDP-glucuronyltransferase activity, which was measured as that responsible for the glucuronidation of thyroxine, were evident following 7-day high-dose administration of all the proton pump inhibitors tested. Of the three proton pump inhibitors investigated, o-aminophenol UDP-glucuronyltransferase activity was greatest following the high-dose administration of omeprazole. Androsterone UDP-glucuronyltransferase activity in rats treated with the proton pump inhibitors increased significantly, but these increases were smaller than those of o-aminophenol UDP-glucuronyltransferase. Pantoprazole and omeprazole treatment did not affect plasma T4 or T3 significantly, whereas lansoprazole treatment produced marked reductions in plasma T4 but did not affect plasma T3 significantly. After administration of 125I-labeled thyroid hormone to rats treated with the proton pump inhibitors, biliary excretion of radioactivity increased significantly in omeprazole- and lansoprazole-treated rats; these increases were attributed to induction of liver thyroxine UDP-glucuronyltransferase activities. The order of biliary excretion of radioactivity, as well as the o-aminophenol UDP-glucuronyltransferase activity, in the treated animals was: omeprazole > lansoprazole > pantoprazole. Therefore, repeated administration of the proton pump inhibitors increased thyroxine-metabolizing activity via induction of UDP-glucuronyltransferase, and this induction by pantoprazole was less pronounced than that by omeprazole or lansoprazole.

Pharmacokinetics and tolerance of pantoprazole, a proton pump inhibitor after single and multiple oral doses in healthy Japanese volunteers.

The pharmacokinetics and tolerance of pantoprazole were investigated after single (20, 40, 80, and 120 mg) and multiple (80 mg once a day for 7 days) oral administration as enteric-coated tablet formulation to healthy male Japanese volunteers. Pantoprazole was well tolerated with no serious adverse events at all doses. Pantoprazole was rapidly absorbed in the fasted state. The mean maximum concentration in serum (Cmax) ranged from 1.77-9.25 micrograms/ml for the 20-120 mg dose and the mean time to reach Cmax (tmax) ranged from 1.92-2.42 h. The half-life (t1/2) ranged from 0.74-1.16 h. A good linear correlation was found between the administered doses (20-120 mg) and the resulting area under the concentration-time curve (AUC) and Cmax with the correlation coefficients of 0.9088 and 0.9263, respectively. Within 24 h, pantoprazole was excreted into urine as the unchanged drug to a negligible extent. In the multiple dose study, 2 apparent poor metabolizers (PMs) of pantoprazole were observed. The means of Cmax, AUC and t1/2 for these 2 PMs were 1.6, 6.7, and 6.8 times higher than those of the extensive metabolizers (EMs). The pharmacokinetic parameters such as Cmax, AUC, and t1/2 after the 7th oral dose were not significantly different from those after the 1st dose both in the PMs and the EMs, which indicated that there was virtually no drug accumulation.

Identification of major biliary and urinary metabolites of ecabapide in rats.

1. The structures of major biliary and urinary metabolites of ecabapide in rat were identified by comparison with authentic standards using lc-ms and 1H-nmr spectrometry. 2. A major metabolite was found in the bile obtained from rat after an oral dose of 14C-ecabapide and identified as the amidaldehyde derivative. In the urine, two polar metabolites were characterized as the phenolic sulphates. Further, two lipophilic metabolites were identified as alcohol derivatives, and two others as oxamic acids. 3. From these results, it was estimated that the first step in the metabolism of ecabapide in rat was oxidative N-dealkylation to produce the amidaldehyde. This amidaldehyde was further metabolized by two routes, one by reduction of the amidaldehyde into the corresponding alcohol followed by mono-demethylation and subsequent aromatic O-sulphation, the second by oxidation of the amidaldehyde into the oxamic acid followed by mono-demethylation and subsequent aromatic O-sulphation.

Nefiracetam hydroxylation by rat liver microsomes and expressed human cytochrome P450s.

1. The metabolism of nefiracetam, a novel cognition-enhancer, by rat liver microsomes has been studied. 2. Formation of 5-hydroxy (5-OH-NEF) and hydroxymethyl (HM-NEF) derivatives was the principal pathway of NEF oxidation in male rats, and followed Michaelis-Menten kinetics with Km values of 2.9 and 3.3 mM, and Vmax values of 7.8 and 4.5 nmol/min/mg protein, respectively. 3. Enzymes catalysing the formation of these two major metabolites were examined. 5-OH-NEF formation was inhibited by antibody to rat CYP3A2 by 60%, and antibodies to CYP2B1, CYP2C11 and CYP2E1 also showed 15-25% inhibition of the formation of 5-OH-NEF. The formation of HM-NEF was inhibited by antibodies to CYP2C11 and CYP2B1 by 80% and 35%, respectively. These findings indicate that CYP3A plays a major role in the formation of 5-OH-NEF, and CYP2B, CYP2C11 and CYP2E1 are also involved to some extent in the 5-hydroxylation, and that CYP2C11 is mainly responsible for HM-NEF formation, and CYP2B is also involved in that catalysis in male rats. The results from the studies of the effects of various chemical inducers, of selective substrates or inhibitors of P450s on the formation of these metabolites also supported these latter findings. 4. NEF metabolism in microsomes prepared from B-lymphoblastoid cells expressing human cytochrome P450s showed that 5-OH-NEF formation by CYP3A4 is the principal metabolic pathway in humans.

Simple and selective assay of 4-hydroxymephenytoin in human urine using solid-phase extraction and high-performance liquid chromatography with electrochemical detection and its preliminary application to phenotyping test.

A simple and selective HPLC method for the determination of 4-hydroxymephenytoin (4-OH-M) in human urine, using a controlled potential coulometric detector equipped with a dual working electrode cell of fully porous graphite, has been developed. After acid hydrolysis of urine, 4-OH-M and the internal standard (I.S.), 5-hydroxy-1-tetralone, were extracted from urine by means of a Bond Elut Certify LRC column. The extracts were chromatographed on a reversed-phase mu Bondapak C18 column using methanol-50 mM KH2PO4 (pH 4.0) (30:70, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. Electrochemical detection at applied potential of 800 mV resulted in a limit of quantitation of 0.76 micrograms/ml. The method showed a satisfactory sensitivity, precision, accuracy, recovery and selectivity. The present method was applied to the phenotyping test in thirteen Japanese healthy volunteers who received an oral 100-mg racemic mephenytoin. The phenotypes determined by the present method were found to be in agreement with those obtained with the reported customary assay based on gas chromatography.

Pharmacokinetics and stability of caldiamide sodium in rats.

Gadodiamide (CAS 122795-43-1) injection (Omniscan) is a formulation composed of gadolinium (III) complexed with diethylenetriaminepentaacetic acid bis-methylamide (Gd DTPA-BMA) and the sodium calcium complex of the same ligand, known as caldiamide sodium (CAS 122760-91-2, NaCa DTPA-BMA), in a molar ratio of 20:1. Following intravenous dosing of NaCa DTPA-BMA (0.015 mmol/kg) in a 14C-labeled form, plasma concentrations of the drug declined rapidly with an elimination half-live of 0.31 h, a distribution volume of 244 ml/kg and a plasma clearance of 9.2 ml/min/kg. These results demonstrate that NaCa DTPA-BMA distributes into the extracellular fluid compartment and is renally excreted via glomerular filtration. Of the dose of radioactivity given, 86.6% was excreted in urine by 4 h after injection, and 95.3% in urine and 3.3% in feces by 120 h. In addition, experiments were done to clarify the in vivo metabolism of NaCa DTPA-BMA. Results show small quantities of transchelatd forms of NaCa DTPA-BMA in urine. HPLC analysis demonstrated these metabolites were the Zn and Cu forms of the drug, resulting from displacement of the Ca ion in the NaCa DTPA-BMA molecule by endogeneous Zn or Cu. Further analyses by HPLC and ICP-AES demonstrate that the unchanged parent drug, the Zn and the Cu forms occur in relative quantities of approximately 92%, 7%, and 1%, respectively. This demonstrates that the Ca ion in caldiamide sodium can be replaced by Zn or Cu ions in vivo, but only to a small extent.

Placental transfer and milk secretion of gadodiamide injection in rats.

The disposition of gadodiamide (CAS 122795-43-1) injection (Omniscan), a nonionic paramagnetic contrast-enhancing medium developed for magnetic resonance imaging, was characterized in the pregnant and lactating rat. After a single intravenous dose of 0.3 mmol/kg 14C-labeled gadodiamide to rats on day 18 of gestation, the maximum levels of radioactivity in the fetus were attained at 5 min, and were approximately 170 times lower than those in the maternal plasma. The AUC ratio of fetal to maternal blood was less than 0.1. Moreover, the distribution percentage of radioactivity in the fetus were on the average 0.01% of the administered dose up to 4 h, and trace amounts of radioactivity were present in fetal tissues at 24 h after dosing. Whole body autoradiography showed that the smallest amounts of radioactivity were present in the fetus, whereas the highest concentrations of radioactivity were noted in the fetal membrane and the kidney at 24 h after dosing. These results indicate that exposure of the developing rat fetus to gadodiamide after maternal drug administration is quantitatively small. The radioactivity levels in the milk increased with time, reaching a maximum 1 h after dosing, and gradually decreased to levels below detection limits over 8 h. A comparison of the AUCs of milk and plasma showed the comparatively small amounts of the drug excreted into milk.

Pharmacokinetics and tolerance of a new fluoroquinolone antimicrobial drug after single oral doses in healthy volunteers.

1. The pharmacokinetics and tolerance of DV-7751a were investigated in healthy male Caucasian volunteers after single oral doses (100, 200, 400 and 800 mg). 2. DV-7751a was rapidly absorbed in the fasted state. The mean maximum concentration in plasma (Cmax) ranged from 0.27 to 1.98 micrograms/ml for the 100-800-mg dose and the mean time to reach Cmax (tmax) ranged from 1.1 to 1.9 h. The terminal half-life ranged from 8.75 to 10.0 h. A good linear correlation (r = 0.974) was found between doses from 100 to 800 mg and the resulting area under the concentration-time curve (AUC). The plasma protein binding of the drug was in the range of 57-65%. 3. Within 48 h, the cumulative urinary excretion of unchanged drug amounted to 22.0-26.8% of the dose administered. Faecal recovery of the drug up to 72 h after the 400-mg dose was about 12% of the dose given. 4. Adverse events thought to be possibly related to the drug included headache, rash, leg cramp, diarrhoea, abdominal pain, CNS depression and dizziness. DV-7751a, however, was well tolerated with no serious adverse events at any doses and all subjects completed the study. No drug crystals were observed in the urine.

Isolation and identification of seven metabolites of a water-soluble platelet aggregation inhibitor in rat urine.

1. Seven metabolites of 7-piperidino-1,2,3,4,5-tetrahydroimidazo[2,1- b]quinazolin-2-one dihydrochloride monohydrate (DN-9693) were isolated from rat urine by extraction with Amberlite XAD-2 and purification by silica gel and Sephadex LH-20 open-column chromatography and preparative high-performance liquid chromatography (hplc). The structure assignment of the metabolites was performed by field desorption mass spectrometry and 200-MHz Fourier transform nmr spectroscopic analysis and comparison with authentic standards when available. 2. DN-9693 underwent metabolism mainly at the piperidine ring to give the 4-hydroxypiperidine derivative (III) and 2-hydroxy-piperidine derivative, which is further metabolized to lactam (II) or delta-aminovaleric acid (V). The acyl side chain of V was shortened by beta-oxidation to form the 3-aminopropionic acid derivative (VII). V and/or VII underwent oxidative dealkylation to give the 7-amino derivative, which was conjugated with acetic acid to form the 7-acetylamino derivative (IV). DN-9693 also underwent hydrolysis of its lactam moiety to give VI. 3. The urinary excretion of III, V and VII was determined by liquid chromatography/electrochemistry (LC/EC) and V proved to be the major metabolite in rat urine. 4. A procedure is also presented for the identification of DN-9693 metabolites using LC/EC.

Pharmacokinetics of SN-38 [(+)-(4S)-4,11-diethyl-4,9-dihydroxy-1H- pyrano[3',4':6,7]-indolizino[1,2-b]quinoline-3,14(4H,12H)-dione], an active metabolite of irinotecan, after a single intravenous dosing of 14C-SN-38 to rats.

Irinotecan (CPT-11) is a camptothecin derivative used for the treatment of cancer. It is a prodrug that is metabolized to its active form, SN-38 [(+)-(4S)-4,11-diethyl-4,9-dihydroxy-1H-pyrano[3',4':6,7]- indolizino[1,2-b]quinoline-3,14(4H,12H)-dione]. To clarify the pharmacokinetic difference between CPT-11 and SN-38, the plasma levels, tissue distribution and excretion of SN-38 were investigated after dosing rats with 14C-labeled SN-38. The plasma radioactivity showed bi-exponential decay with a terminal half-life of 9.91 h. TLC separation revealed that the plasma radioactivity consisted mainly of SN-38 at 5 min after dosing; however, it was soon replaced with SN-38 glucuronide (SN-38 Glu) and an unknown metabolite (M-2). The half-life of unchanged SN-38 after dosing with SN-38 was about 7 min, which was much shorter than that after dosing with CPT-11 (2.8 h) as reported previously. Its radioactivity was excreted mainly in feces (70.0% within 168 h), and biliary excretion (64.1% within 48 h) could account for the fecal excretion. The major component of urinary and biliary radioactivity was found by TLC to be SN-38. Whole body autoradiograms revealed that the tissue distribution of the radioactivity was low except in the liver and kidney. The radioactivity decreased rapidly and little was found in the body 24 h after dosing. In conclusion, SN-38 was excreted rapidly from bile and showed poor tissue distribution. These characteristics lead to a shorter SN-38 half-life, more so than dosing with CPT-11.

Biliary metabolites of semotiadil fumarate in the rat.

After oral administration of 14C-semotiadil fumarate to rat, 81.3% of the dosed radioactivity was excreted into the bile. Five major biliary metabolites were detected and characterized as phenolic O-glucuronides by FAB mass spectrometry and 1H-nmr spectrometry. From these results it was concluded that the first step in the metabolism of semotiadil in rat was oxidations at various portions around the molecule to produce phenols. These oxidations implied the ring-opening of the methylenedioxy ring, O-demethylation of the methoxybenzene, hydroxylation of the ring, and aromatic N-demethylation. The next step was O-glucuronidation of the resulting intermediate phenolic metabolites.

Metabolism of irinotecan to SN-38 in a tissue-isolated tumor model.

The objective of this study is to investigate the metabolism of the antitumor drug, irinotecan (CPT-11), to its active metabolite, SN-38, in tumor tissue. Using Walker 256 carcinoma, we prepared a tissue-isolated tumor model: tumor preparation was continuously perfused with Krebs-Henseleit bicarbonate buffer containing 4% bovine serum albumin (BSA) and CPT-11 (10 micrograms/ml), and the concentration of SN-38 in the perfusate was monitored using HPLC. The concentration of SN-38 in the perfusate was gradually increased to a level of 9.69 ng/ml 60 min after the start of perfusion. As a control, an aliquot of the perfusate was separately incubated; however, no significant increase in SN-38 levels was observed. At the end of the perfusion, a part of the tumor tissue was homogenized and the level of SN-38 was determined; the levels in tumor tissue were 2.2-4.5 times higher than in the perfusate. From above results, CPT-11 was found to be metabolized to its active metabolite, SN-38, in tumor tissue--a desirable feature of an antitumor prodrug.

In vitro metabolism of nefiracetam by liver microsomes from rats, dogs and monkeys.

The in vitro metabolism of nefiracetam (CAS 77191-36-7, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, NEF, DM-9384), a novel cognition enhancer, has been investigated using liver microsomes from rats, dogs and monkeys. Microsomal metabolism of NEF showed qualitatively a similar profile in three species tested. Six metabolites were generated from incubation of NEF with liver microsomes. Their structures were identified using a thermospray LC/MS/MS (liquid chromatography/tandem mass spectrometry) method, as regioisomers of monhydroxylated derivatives of NEF: the 3-hydroxy (3-OH-NEF); 4-hydroxy (4-OH-NEF); 5-hydroxy (5-OH-NEF); 3'-hydroxy (3'-OH-NEF); 4'-hydroxy (4'-OH-NEF); hydroxymethyl (HM-NEF) metabolites. The heat lability, NADPH requirement and inhibition by prototype cytochrome P450 inhibitors (proadifen and metyrapone) implies that NEF oxidations are catalyzed by cytochromes P450. The major metabolic route was 5-OH-NEF formation in all species, corresponding well with the previous investigations in vivo. Inhibitory effects of alpha-naphthoflavone and quinidine on NEF hydroxylation suggest that several isoforms of cytochromes P450 are involved in the formation of these NEF metabolites.