Pharmacokinetics and metabolism of NO-1886, a lipoprotein lipase-promoting agent, in cynomolgus monkey

1. The study was conducted to investigate the pharmacokinetics and metabolism of NO-1886 (diethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) in cynomolgus monkeys. 2. After single intravenous administration of NO-1886 at a dose of 3 mg kg(-1), the total clearance (CL(tot)), area under the plasma concentration-time curve (AUC(0-)(t)), half-life (t(1/2)), and volume of distribution (V(d)) in cynomolgus monkeys were 531 ml h(-1) kg(-1), 5.63 micro g h ml(-1), 0.96 h and 679 ml kg(-1), respectively. The AUC(0-)(t) for oral administration of NO-1886 (3 mg kg(-1)) was 4.23 micro g h ml(-1) and the bioavailability was 75%. 3. M-2 (ethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) and M-3 (4-[(diethoxy-phosphoryl) methyl)] benzoic acid) were present as metabolites in plasma and urine. In faeces, M-2 was present but M-3 was not. 4. The major metabolite of NO-1886 in liver S9 or microsomes was M-2 in the presence of NADPH. On the other hand, M-3 was formed in the absence of NADPH in liver S9 or microsomes and its formation was inhibited by bis-( p-nitrophenyl) phosphate (BNPP) in liver S9, suggesting that the formation of M-3 was catalysed by carboxylesterase. 5. The findings suggest that the main metabolic pathway of NO-1886 in cynomolgus monkeys is the O-deethylation of NO-1886 to M-2, as in rats and humans, and that the hydrolysis of the amide bond is a minor metabolic pathway.     

Deuterium isotope effect on the toxicokinetics of monomethylamine in the rat

The single-dose toxicokinetics of monomethylamine has been characterized in the rat by HPLC assay of serial blood samples. Biphasic first-order elimination was observed following an iv bolus dose of 19 mumol/kg with a terminal half-life of 19.1 +/- 1.3 min (mean +/- SE, N = 4). The apparent steady state volume of distribution, systemic blood clearance, and renal blood clearance were 1.21 +/- 0.09 liter/kg, 53.4 +/- 3.5 ml/min/kg, and 5.72 +/- 0.53 ml/min/kg, respectively. The administration of an intragastric dose permitted the calculation of the systemic bioavailability of monomethylamine as 69 +/- 3%. Duplicate experiments using the structural analogue with deuterium atoms substituted for hydrogens on the methyl group revealed a much slower elimination of the compound, although ultimately, 5 times as much was excreted unchanged in the urine. Isotope effects calculated as the ratios of terminal half-life, systemic blood clearance, and systemic bioavailability were 1.9, 2.2, and 1.8, respectively.     

Pharmacokinetics and metabolism of the reactive oxygen scavenger alpha-phenyl-N-tert-butylnitrone in the male Sprague-Dawley rat.

The pharmacokinetics of the spin-trap alpha-phenyl-N-tert-butylnitrone (PBN) was investigated in male Sprague-Dawley rats. Plasma concentrations after i.v. administration (10 mg/kg) declined monoexponentially with a terminal half-life of 2.01 +/- 0.35 h and total plasma clearance (CL(p)) and volume of distribution at steady state (Vd(ss)) averaged 12.37 +/- 3.82 ml/min/kg and 1.74 +/- 0.5 l/kg, respectively. The observed CL(p) was in close agreement with the blood clearance (CL(b)) value (11.5 ml/min/kg) predicted from in vitro liver microsomal incubations suggesting that PBN CL(p) in rats is predominantly due to hepatic metabolism. Peak plasma concentration (C(max)) following p.o. (20 mg/kg) and s.c. (30 mg/kg) PBN administration was 7.35 +/- 1.92 and 3.56 +/- 0.66 microg/ml, whereas the area under the concentration-time curve from 0 to infinity was 23.89 +/- 5.84 and 15.96 +/- 3.10 microg-h/ml, respectively. The mean oral bioavailability of PBN was 85.63 +/- 20.93%. Biotransformation studies indicated the P450 2C11-catalyzed hydroxylation of PBN to M1. Potential sites of hydroxylation included the benzylic carbon resulting in phenyl-N-tert-butylhydroxamic acid or the phenyl ring that would afford alpha-hydroxyphenyl-N-tert-butylnitrone (HOPBN). The structure of M1 was established as alpha-4-Hydroxyphenyl-N-tert-butylnitrone (4-HOPBN) on the basis of: 1) obvious LC R(t) differences between M1 and the authentic hydroxamate standard, 2) P450 catalyzed hydroxylation of [(2)H]PBN that contained a deuterium instead of a hydrogen atom on its benzylic position and which afforded [(2)H]M1, and 3) comparison of the liquid chromatography-tandem mass spectrometry properties with a synthetic 4-HOPBN standard. We speculate that 4-HOPBN is an "active" PBN metabolite that provides an additive effect to the pharmacological action of PBN in vivo.     

Enterohepatic recirculation and renal metabolism of morphine in the rat.

Morphine (2.5 mg/kg) was administered iv to intact (I), bile duct-cannulated (BC), and bile duct-cannulated--renal-ligated (BC-RL) rats (n = 4 per group) to investigate the extent of enterohepatic recirculation and renal metabolism of the drug. A decrease in the serum area under the concentration-time curve (AUC) was observed for the BC in comparison with I rats. From these AUC values, it was determined that approximately 16% of the administered dose was subject to enterohepatic recirculation. In addition, a statistically significant (p less than 0.05) decrease in the systemic clearance of morphine was observed in the BC-RL rats compared with the BC animals (55.2 +/- 17.2 versus 31.4 +/- 8.5 mL/min/kg). This decrement in systemic clearance appeared to be the result of a significant decrease in the formation clearance of morphine glucuronide after ligation of the renal pedicles (23.2 +/- 4.8 versus 10.9 +/- 5.0 mL/min/kg). Renal metabolic clearance was calculated as 15.7 mL/min/kg, accounting for 28.5% of the systemic clearance of morphine. Hepatic clearance (31.4 +/- 8.5 mL/min/kg) accounted for 56.8% of total systemic clearance.     

Metabolism of a new dihydropyridine calcium antagonist in rats and dogs

1. The metabolism of a new dihydropyridine calcium channel blocker was studied in rats and dogs. The drug was extensively metabolized by both species after oral dosing. Metabolites were detected by two-dimensional t.l.c. after dosing with the 14C-labelled drug. Urinary metabolite patterns were quantitatively different in rats and dogs. 2. Ten metabolites were isolated from urine, bile and liver homogenate of male or female rats, and identified. 3. The main metabolic pathway was oxidation of the dihydropyridine moiety to the pyridine form, followed by the hydrolysis of the ester, oxidation of the methyl group at the 6-position, and oxidation of the isopropyl group. Other pathways were hydrolysis of the 3-isopropyl ester or 5-methyl ester group to the dihydropyridine monocarboxylic acid (M-2 and M-10, respectively). 4. The drug was metabolized in rats stereoselectively. M-2 and M-10 isolated from rat female urine were analysed by chiral stationary-phase h.p.l.c. and were mainly the enantiomers derived from (-)- and (+)-drug, respectively.     

Metabolism of a new dihydropyridine calcium antagonist in rats and dogs

1. The metabolism of a new dihydropyridine calcium channel blocker was studied in rats and dogs. The drug was extensively metabolized by both species after oral dosing. Metabolites were detected by two-dimensional t.l.c. after dosing with the ¹⁴C-labelled drug. Urinary metabolite patterns were quantitatively different in rats and dogs.

2. Ten metabolites were isolated from urine, bile and liver homogenate of male or female rats, and identified.

3. The main metabolic pathway was oxidation of the dihydropyridine moiety to the pyridine form, followed by the hydrolysis of the ester, oxidation of the methyl group at the 6-position, and oxidation of the isopropyl group. Other pathways were hydrolysis of the 3-isopropyl ester or 5-methyl ester group to the dihydropyridine monocarboxylic acid (M-2 and M-10, respectively).

4. The drug was metabolized in rats stereoselectively. M-2 and M-10 isolated from rat female urine were analysed by chiral stationary-phase h.p.l.c. and were mainly the enantiomers derived from (-)- and (+)-drug, respectively.     

Altered oral absorption of alcohol by combined aqueous extracts of four herbal plants in rats

This study examined the effect of combined aqueous extracts (BHR) of Ginko biloba, Mentha arvensis var. piperascens, Citrus unshiu, and Pueraria lobata var. chinensis on oral absorption of alcohol in rats. The rats were pretreated with BHR, placebo solution identical to BHR without the herbal extract, and isotonic saline. Alcohol was administered orally at 1- and 3-g/kg doses and the absorption profiles were compared. After oral administration of 1-g/kg doses, mean area under the curve (AUC) and C(max) values were significantly reduced in BHR-treated rats (16.1 +/- 10.0 and 0.3 +/- 0.1 mg/ml, respectively) as compared with saline-treated (37.9 +/- 14.4 and 0.7 +/- 0.7 mg/ml, respectively) and placebo solution-treated (63.0 +/- 46.4 and 0.7 +/- 0.4 mg/ml, respectively) rats. Similarly, after administration of 3-g/kg doses, mean AUC and C(max) values in BHR-treated rats (188.1 +/- 119.7 mg(.)min/ml and 1.0 +/- 0.4 mg/ml) were significantly reduced over those in saline-treated rats (571.4 +/- 512.4 mg(.)min/ml and 1.8 +/- 0.9 mg/ml, respectively). The relative oral bioavailability of alcohol calculated as the ratio of AUC(BHR)/AUC(Saline) was 42.5% and 32.9% at 1- and 3-g/kg doses, respectively. The reduced serum alcohol levels as well as the reduced AUC and C(max) after pretreatment with BHR appear to be a result of a reduced systemic absorption not due to an increased metabolic clearance.     

Intravenous pharmacokinetics, oral bioavailability and dose proportionality of ragaglitazar, a novel PPAR-dual activator in rats

Pharmacokinetics of ragaglitazar (a novel phenoxazine derivative of aryl propanoic acid), a potent insulin sensitizing and lipid-lowering compound was studied in Wistar rats. A single dose of 1, 3 or 10 mg/kg of ragaglitazar was given orally to male rats (n=4 per dose level) to evaluate dose proportionality. In another study, a single intravenous bolus dose of ragaglitazar was given to rats (n=4) at 3 mg/kg dose following administration through the lateral tail vein in order to obtain the absolute oral bioavailability and clearance parameters. Blood samples were drawn at predetermined intervals and the concentration of ragaglitazar in plasma was determined by a validated HPLC method. Plasma concentration versus time data were generated following oral and intravenous dosing and pharmacokinetic analysis was performed using non-compartmental analysis. The results revealed that Cmax and AUC(0-infinity) increased more than proportionally to the administered oral doses. As dose increased in the ratio of 1:3:10, the mean Cmax and AUC(0-infinity) increased in the ratio of 1:3.2:13 and 1:3.2:16, respectively. After intravenous administration the systemic clearance and volume of distribution of ragaglitazar in rats were 139+/-30 ml/h/kg and 463+/-51 ml/kg, respectively (mean+/-SD). Plasma concentrations declined mono-exponentially following intravenous administration and elimination half-life (t1/2) was about 2.6 h and not significantly different (p > 0.05) from the value from oral administration. Mean residence time (MRT) values for ragaglitazar were found to be 4.15+/-0.52 h (3.5 to 4.6 h). Absolute oral bioavailability of ragaglitazar across the doses tested was in the range of 68%-93%. In conclusion, ragaglitazar exhibits promising pharmacokinetic properties in rats.     

Effect of experimental renal failure on the pharmacokinetics of losartan in rats

The purpose of this investigation was to determine whether the pharmacokinetics of the angiotensin II receptor antagonist losartan is altered in renal failure. Male Wistar rats were pretreated with uranyl nitrate or subjected to bilateral ureteral ligation to produce acute renal failure (ARF). Saline-injected and sham-operated rats, respectively, served as controls. Uranyl nitrate-treated rats showed significantly higher serum concentrations of losartan after oral administration and the area under the serum concentration-time curve (AUC(0-24)) of losartan increased about 3-fold compared to control rats. The systemic clearance of losartan significantly decreased from 410 +/- 254ml/h/kg in control to 177 +/- 112ml/h/kg in uranyl nitrate-treated rats. In order to investigate the mechanisms of reduced clearance of losartan associated with ARF, a hepatic microsome fraction was prepared from normal and ARF rats. No significant difference was found in the metabolism of losartan by hepatic microsomes prepared from ARF and control rats. In addition, the metabolic activity of microsomes was examined in the presence of uremic rat serum. The unbound clearance of losartan and the unbound clearance associated with the formation of EXP3174 in the presence of uremic serum were significantly lower than those in the presence of control serum. Furthermore, the metabolism of losartan was inhibited by indoxyl sulfate, a uremic toxin, in an uncompetitive manner. These results suggest that ARF is associated with reduced clearance of losartan due to the inhibition of hepatic metabolism by accumulated uremic toxin(s).     

Role of NK1 receptors on cisplatin-induced nephrotoxicity in the rat

The role of NK1 receptors on the nephrotoxicity associated with cisplatin treatment was evaluated. Adult Sprague-Dawley male rats (300-400 g) were treated with saline (0.1 ml/100 g, i.p., every 8 h for 72 h) or the selective NK1 receptor antagonist (GR205171; 2 mg/kg, i.p., every 8 h for 72 h). Treatments were started 5 min before cisplatin (7.5 mg/kg, i.p., single dose). All evaluations were made from 72 h to 96 h after cisplatin. An oral load of 10 ml/kg of water was given at time 0 (72 h after cisplatin). Cisplatin reduced the urinary volume (-45%), creatinine clearance (>90%), lithium clearance (-76%) and urinary potassium excretion (-54%). Protein and sodium excretion was not affected by cisplatin. GR205171 prevented the reduction in urine volume induced by cisplatin. In addition, the decreases in creatinine and lithium clearances induced by cisplatin were also attenuated by the NK1 receptor antagonist. The clearance of creatinine averaged 0.57+/-0.2 ml/min in controls, 0.004+/-0.01 ml/min after cisplatin, and 0.09+/-0.02 ml/min after cisplatin + GR205171. The lithium clearance was 0.09+/-0.04 ml/min in controls, 0.02+/-0.01 ml/min after cisplatin and 0.06+/-0.01 ml/min after cisplatin + GR205171. Cisplatin induced marked necrosis, vacuolation and edema of proximal renal tubules; these changes were considerably reduced in GR205171-treated animals. These results indicate that treatment with a selective NK1 receptor antagonist ameliorated cisplatin-induced renal toxicity in rats, as evidenced by improvements in renal function and histology.     

Preclinical pharmacokinetics and metabolism of 6-(4-(2,5-difluorophenyl)oxazol-5-yl)-3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine, a novel and selective p38alpha inhibitor: identification of an active metabolite in preclinical species and human liver microsomes

The disposition of 6-(4-(2,5-difluorophenyl)oxazol-5-yl)-3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine (1), a potent and selective inhibitor of mitogen activated protein (MAP) kinase p38alpha, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 1 demonstrated generally favorable pharmacokinetic properties in all species examined. Following intravenous (i.v.) administration, 1 exhibited low volumes of distribution at steady state (Vd(ss)) ranging from 0.4-1.3 l/kg (2.4-26 l/m(2)) in the rat, dog and monkey. Systemic plasma clearance was low in cynomolgus monkeys (6.00 ml/min/kg, 72.0 ml/min/m(2)) and Sprague-Dawley rats (7.65+/-1.08 ml/min/kg, 45.9+/-6.48 ml/min/m(2) in male rats and 3.15+/-0.27 ml/min/kg, 18.9+/-1.62 ml/min/m(2) in female rats) and moderate in beagle dogs (12.3+/-5.1 ml/min/kg, 246+/-102 ml/min/m(2)) resulting in plasma half-lives ranging from 1 to 5 h in preclinical species. Moderate to high bioavailability of 1 was observed in rats (30-65%), dogs (87%) and monkeys (40%) after oral (p.o.) dosing consistent with the in vitro absorption profile of 1 in the Caco-2 permeability assay. In rats, the oral pharmacokinetics were dose dependent over the dose range studied (5, 50 and 100 mg/kg). The principal route of clearance of 1 in rat, dog, monkey and human liver microsomes and in vivo in preclinical species involved oxidative metabolism mediated by cytochrome P450 enzymes. The major metabolic fate of 1 in preclinical species and humans involved hydroxylation on the isopropyl group to yield the tertiary alcohol metabolite 2. In human liver microsomes, this transformation was catalysed by CYP3A4 as judged from reaction phenotyping analysis using isozyme-specific inhibitors and recombinant CYP enzymes. Metabolite 2 was also shown to possess inhibitory potency against p38alpha in a variety of in vitro assays. 1 as well as the active metabolite 2 were moderately to highly bound to plasma proteins (f(u) approximately 0.1-0.33) in rat, mouse, dog, monkey and human. 1 as well as the active metabolite 2 did not exhibit competitive inhibition of the five major cytochrome P450 enzymes namely CYP1A2, 2C9, 2C19, 2D6 and 3A4 (IC(50)>50 microM). Overall, these results indicate that the absorption, distribution, metabolism and excretion (ADME) profile of 1 is relatively consistent across preclinical species and predict potentially favorable pharmacokinetic properties in humans, supporting its selection for toxicity/safety assessment studies and possible investigations in humans as an anti-inflammatory agent.     

Prediction of metabolic clearance of bisphenol A (4,4 '-dihydroxy-2,2-diphenylpropane) using cryopreserved human hepatocytes.

This study investigated the kinetics of glucuronidation of bisphenol A (BPA; 4,4'-dihydroxy-2,2-diphenylpropane) in cryopreserved human hepatocytes (HCs). Incubation conditions were developed using Sprague-Dawley rat HCs. For determination of the kinetic constants of BPA glucuronidation rates with human HCs, viable HCs (0.125 x 10(6)) were incubated with [(14)C]BPA (1.3-52 microM) for 10 min. The glucuronidation reaction demonstrated Michaelis-Menten kinetics and yielded a mean K(m) for males and females of 9 +/- 3 and 8 +/- 2 microM, respectively. The V(max) values of these reactions were 438 +/- 129 pmol/min/10(6) for male HCs and 480 +/- 208 pmol/min/10(6) for female HCs. The scaled intrinsic clearance (CL(int)) for male human HCs was 149 +/- 67 ml/min/kg (range 53-246) and for female HCs was 165 +/- 89 ml/min/kg (range 73-336). Overall, there are no apparent gender differences in the glucuronidation of BPA. These CL(int) values were then extrapolated to estimate total hepatic metabolic clearance (CL(met)) using a nonrestrictive well stirred model. The estimated CL(met) value for both male and female HCs was 6 ml/min/kg, which represents 30% of hepatic blood flow. Thus, in vivo clearance seems to depend highly on plasma protein binding. These in vitro results correlate well with in vivo studies in humans, which report extensive glucuronidation of BPA.     

Differential pharmacokinetics of acetohexamide in male Wistar-Imamichi and Sprague-Dawley rats: role of microsomal carbonyl reductase

Acetohexamide (AH) is reduced to its alcohol metabolite by carbonyl reductase. We have previously shown that carbonyl reductase present in the liver microsomes of rats is a male-specific and androgen-dependent enzyme. In the present study, the role of microsomal carbonyl reductase in the pharmacokinetics of AH was examined in male Wistar-Imamichi (WI) and Sprague-Dawley (SD) rats after its intravenous administration. AH was eliminated more slowly from plasma in the WI strain, which lacks most of the microsomal carbonyl reductase, than in the SD strain. Furthermore, several pharmacokinetic parameters were derived from the data for the plasma concentrations of AH. The plasma clearance (CL(p)) of AH (72.8+/-11.2 ml/h/kg) in male WI rats was significantly smaller than that (105.5+/-11.1 ml/h/kg) in male SD rats. Testectomy caused a marked decrease, from 105.5+/-11.1 to 44.3+/-11.8 ml/h/kg, in the CL(p) of AH in male SD rats. These results indicate that microsomal carbonyl reductase plays a critical role in the differential pharmacokinetics of AH in male WI and SD rats.     

No effect of phenobarbital pretreatment of rats on methotrexate pharmacokinetics in the isolated liver perfused in a single-pass way

Pretreatment of the rat with phenobarbital (PB) is known to increase gene expression of the canalicular multispecific organic anion transporter (cMOAT) and hepatobiliary transport of its substrates (glutathione, sulfobromophthalein). To determine the effect of PB on the hepatobiliary transport of methotrexate (MTX, another substrate of cMOAT) and its metabolism to 7-hydroxymethotrexate (7-OHMTX) in the rat, we compared the steady-state pharmacokinetics of MTX in the isolated liver of either PB-pretreated (80 mg/day/kg bw for 4 days, i.p.) or nonpretreated rats. The livers were perfused in a single-pass way at a flow rate of 15 ml/min using a perfusate which consisted of Krebs-Henseleit buffer containing glucose, taurocholate, bovine albumin and erythrocytes. During the perfusion with 50 micromol/l MTX, the steady-state biliary clearance (1.26 +/- 0.24 ml/min) in 7 nonpretreated rats accounted for a major proportion of the hepatic clearance (1.30 +/- 0.33 ml/min), metabolism of MTX to 7- OHMTX was minor (partial metabolic clearance = 0.041 +/- 0.023 ml/min). MTX concentrations in bile surpassed those in the input perfusate by approximately 100-fold. Pretreatment of rats (n = 7) with PB did not change significantly the steady-state hepatic, biliary and partial metabolic clearances of 50 micromol/l MTX. An interesting result is a 38% increase in the hepatic vascular resistance of non-pretreated livers caused by MTX. The results suggest that in rats, pretreatment with PB has no effect on the hepatobiliary transport and hydroxylation of MTX.     

Impairment of lidocaine clearance in elderly male subjects

Six elderly male (65-75 years), seven elderly female (64-88 years), 15 young male (22-38 years), and nine young female (25-37 years) volunteers, all of normal body weight and clinically without cardiac or renal dysfunction, received a single 25-mg intravenous dose of lidocaine. Plasma concentrations of lidocaine were determined from blood samples drawn during 8 h following the lidocaine dose. Elimination half-life (t1/2) was markedly prolonged in elderly male subjects as compared with that in young male subjects (mean +/- SE: 2.70 +/- 0.21 versus 1.66 +/- 0.09 h; p less than 0.001). No difference in t1/2 was noted among female subjects (2.27 +/- 0.21 versus 2.07 +/- 0.07 h). Volume of distribution was greater in women than in men but was not influenced by age. Instead, prolongation in t1/2 in elderly men was the result of a highly significant decrease in total metabolic clearance (12.9 +/- 2.0 versus 19.8 +/- 1.5 ml/min/kg; p less than 0.05). No significant change in total metabolic clearance of lidocaine was noted between elderly and young women (18.3 +/- 2.0 versus 21.1 +/- 1.6 ml/min/kg). The findings suggest that in the elderly male patient without evidence of congestive heart failure or other coexisting chronic disease, the initial loading dose of lidocaine should be the same as for a young patient. However, to achieve comparable plasma concentrations and therapeutic effect during continuous infusion therapy, the elderly male patient should have the continuous infusion rate decreased by an average of at least 35%.     

Pharmacokinetics of triflusal and its main metabolite in rats and dogs.

The methods for determining plasma concentrations of triflusal (2-acetoxy-4-trifluoromethyl benzoic acid) that have been described, do not distinguish between the drug and its main metabolite HTB (2-hydroxy-4-trifluoromethyl benzoic acid). In the present study, we have developed a new analytical technique based on HPLC that enabled us to carry out a pharmacokinetic study of the drug and its metabolite in animals. An intravenous or oral dose of 50 mg/kg was administered to male Sprague-Dawley rats, and 15 mg/kg was administered to beagle dogs. Plasma levels of triflusal and HTB were determined. In rats, triflusal was quickly eliminated from plasma with a biological half-life (t1/2) of 2.7 min and a clearance (Cl) of 73.4 (ml/kg)/min. The elimination of HTB was much slower with a t1/2 of 21.5 h and a Cl of 5.1 (mg/kg)/h. The maximum concentration (Cmax) of triflusal in rats after an oral administration was 8.1 +/- 2.0 micrograms/ml reached between 2.5 and 10 min. The Cmax of HTB was 237.7 micrograms/ml and was achieved at 0.7 h. The bioavailability of triflusal in rats was only 10.6% while the bioavailability of HTB was more than 100% indicating an important first pass effect. In dogs the t1/2 of triflusal was 14.4 +/- 5.9 min and the Cl was 25.1 +/- 4.7 (ml/kg)/min. HTB was also eliminated very slowly with a t1/2 of 71.1 +/- 12.5 h and a Cl of 2.4 +/- 0.3 (ml/kg)/h. The Cmax of triflusal in dogs was 13.3 +/- 2.9 micrograms/ml and was reached after 19.2 +/- 6.1 min (tmax).(ABSTRACT TRUNCATED AT 250 WORDS)     

Bioavailability and mammary excretion of bisphenol a in Sprague-Dawley rats.

This study reports the absolute oral bioavailability and mammary excretion of bisphenol A in rats. The oral bioavailability was determined after administration of relatively low iv (0.1 mg/kg) and oral (10 mg/kg) doses of bisphenol A to rats. After iv injection, serum levels of bisphenol A declined biexponentially, with the mean initial distribution and terminal elimination half-lives being 6.1 +/- 1.3 min and 52.5 +/- 2.4 min, respectively. The systemic clearance (Cls) and the steady-state volume of distribution (Vss) averaged 107.9 +/- 28.7 m/min/kg and 5.6 +/- 2.4 L/kg, respectively. Upon oral administration, the maximum serum concentration (Cmax) and the time to reach the maximum concentration (Tmax) were 14.7 +/- 10.9 ng/ml and 0.2 +/- 0.2 h, respectively. The apparent terminal elimination half-life of bisphenol A (21.3 +/- 7.4 h) after oral administration was significantly longer than that after iv injection, indicating the flip-flop of the absorption and elimination rates. The absolute oral bioavailability of bisphenol A was low (5.3 +/- 2.1%). To determine the extent of mammary excretion, bisphenol A was given by simultaneous iv bolus injection plus infusion to steady state at low, medium, and high doses. The steady-state serum levels of bisphenol A were linearly increased with higher dosing rates. The systemic clearance (mean range, 119.2-154.1 ml/min/kg) remained unaltered over the dosing rate studied. The levels of bisphenol A in milk exceeded those in serum, with the steady-state milk to serum concentration ratio being 2.4-2.7.     

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: dose-dependent pharmacokinetics in rats

The dose-dependency in the pharmacokinetics of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednisolone succinate (DMP), was investigated in rats. Single doses (MP equivalent) of 2.5, 5.0, 10, 20, and 30 mg/kg of DMP were administered intravenously to rats (n=5/group), and serial blood samples (0-96 h) and spleen and liver tissues (96 h) were collected. The concentrations of DMP in plasma and spleen were analyzed using a size-exclusion chromatographic method. The concentrations of DMP in the liver samples were determined by an indirect method after sequential hydrolysis by dextranase and esterase enzymes, followed by HPLC analysis of MP. The kinetics of DMP were analyzed by non-compartmental methods. The systemic clearance of DMP decreased approximately 5-fold (from 42.1+/-11.0 to 7.72+/-1.84 ml/h per kg) when the dose was increased from 2.5 to 30 mg/kg. The nonlinearity in the clearance of DMP could be adequately described by a Michaelis-Menten type elimination with a maximum velocity of elimination of 1.72 mg/h per kg and a constant of 24.9 microg/ml. Additionally, the percent of the dose of DMP found at 96 h in the liver and spleen, where the prodrug is sequestered and gradually eliminated, significantly decreased with an increase in the dose. It is concluded that the clearance of DMP in rats is modestly dose-dependent in the dosage range of 2.5-30 mg/kg.     

Intraindividual variability in male hepatic CYP3A4 activity assessed by alfentanil and midazolam clearance.

Clinical investigations using isoform-selective probes to phenotype cytochrome P450 activity and interaction studies using isoform-selective inhibitors to determine P450 involvement in drug metabolism assume minimal interday variability in P450 activity. CYP3A4 is the most abundant human P450 isoform and metabolizes approximately half of all therapeutic agents. This investigation evaluated interday variability in hepatic CYP3A4 activity in males, using the clearances of midazolam and alfentanil as metabolic probes. Midazolam (1 mg) followed 1 hour later by alfentanil (20 micrograms/kg) were administered by intravenous bolus to 9 nonsmoking male volunteers (ages 30 +/- 8 years). Drug administration was repeated 12 and 20 days later. Venous plasma midazolam and alfentanil concentrations were determined by gas chromatography/mass spectrometery. Drug clearances were determined by noncompartmental and multiexponential analysis. There were no significant interday differences in plasma drug concentrations or clearances (3.9 +/- 1.4, 3.9 +/- 1.7, and 4.2 +/- 1.7 ml/kg/min for alfentanil, respectively, and 6.6 +/- 2.0, 7.9 +/- 2.4, and 7.9 +/- 2.5 ml/kg/min for midazolam, respectively, on days 1, 13, and 21 [mean +/- SD]). Interday variability in clearance was 13% +/- 6% and 19% +/- 12% for alfentanil and midazolam, respectively. Interday variability in the clearance of these probes, and presumably hepatic CYP3A4 activity, was small compared with interindividual variability. Consideration of interday variability in the hepatic metabolism of CYP3A4 substrates does not appear significant in the design of clinical trials.     

High-performance liquid chromatographic determination of oxatomide and its metabolite and its application to pharmacokinetic study in rat plasma

Oxatomide (CAS 60607-34-3) is an antiallergic agent effective against allergic rhinitis, urticaria, pruritus dermatitis, eczema dermatitis and bronchial asthma. The aim of this study was to establish the method for simultaneously determining oxatomide and its major metabolite M-11 in human serum, human plasma and rat plasma by high-performance liquid chromatography (HPLC). The method was applied to study the influences of alimentation on pharmacokinetics of oxatomide in rats. After extracting oxatomide and its metabolite M-11 from human serum, human plasma or rat plasma with diethyl ether under alkaline condition, sulfuric acid was added to the organic layer and oxatomide and M-11 were back-extracted. The aqueous layers were analysed by HPLC equipped with a fluorimetric detector. The method was highly sensitive and precise for quantitation of oxatomide and M-11 in human serum, human plasma and rat plasma in the concentration range of 1 to 125 ng/ml. Plasma concentration of oxatomide decreased biphasically with an elimination half-life (T1/2) of 1.59 h after intravenous administration of oxatomide (1 mg/kg) to non-fasting male rats. After oral administration of oxatomide (30 mg/kg) to fasting male rats, plasma concentration of oxatomide increased rapidly, and reached the maximum concentration of 188 ng/ml (Cmax) at 1.0 h. Plasma concentration of oxatomide decreased monophasically. The T1/2 was 2.58 h. The bioavailability was 6.74%. Plasma concentration of M-11 increased rapidly, and reached Cmax of 64.3 ng/ml at 0.7 h, and decreased monophasically with T1/2 of 3.79 h. After oral administration of oxatomide to non-fasting male rats, plasma concentration of oxatomide reached Cmax of 378 ng/ml at 3.3 h. The T1/2 was 3.27 h and the bioavailability was 17.5%. The Cmax and AUC0-infinity of M-11 were larger than those after oral administration of oxatomide to fasting male rats. These results demonstrated the usefulness of this method for monitoring and basic examination of biological samples and the influence of alimentation on absorption of oxatomide. Determination of plasma oxatomide concentrations would provide a useful indication of therapeutic efficacy.