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Trandolapril is the prodrug of an angiotensin-converting enzyme (ACE) inhibitor. It has been proposed that its active metabolite, trandolaprilat, is mainly excreted in bile, but this has not been clearly demonstrated. Recently it has been reported that temocaprilat, an active metabolite of the ACE inhibitor temocapril, is effectively excreted in bile via an ATP-dependent active transporter (canalicular multispecific organic anion transporter: cMOAT). To investigate whether trandolaprilat has the pharmacological ability to affect the cMOAT system in a manner similar to temocaprilat. The lipophilicity of trandolaprilat and temocaprilat was measured to determine the n-octanol-water partition coefficients. The dose-dependent inhibition of the uptake of [3H]-estradiol-17β-D-glucuronide and [3H]-2, 4-dinitrophenyl-S-glutathione, which are good substrates for cMOAT, in canalicular membrane vesicles (CMVs) prepared from Sprague-Dawley rats was determined in the presence of trandolaprilat and temocaprilat. The partition coefficient of trandolaprilat (log Po/w−1.1) was about 30 times higher than that of temocaprilat (log Po/w−2.5). The uptake of [3H]-estradiol-17β-D-glucuronide and [3H]-2, 4-dinitrophenyl-S-glutathione was dose-dependently inhibited by the presence of temocaprilat, but trandolaprilat had no effect on the transport of [3H]-estradiol-17β-D-glucuronide or [3H]-2, 4-dinitrophenyl-S-glutathione into CMVs even at concentrations as high as 200μM. It could be concluded that trandolaprilat has a higher lipophilicity than temocaprilat. But the hepatobiliary excretion system via cMOAT may not contribute to the excretion of trandolaprilat in bile. (Hypertens Res 2001; 24: 235-240)

A new method for the determination of pravastatin, a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and its main metabolite (R-416) in human plasma using high-performance liquid chromatography/atmospheric pressure (negative ion) chemical ionization mass spectrometry (LC/APCI-MS) is described. Pravastatin and R-416 in human plasma were isolated using solid phase extraction technique and analyzed by LC/APCI-MS. Selected ion monitoring was employed for selectivity and sensitivity, which enabled the quantification over a range of 0.625-80 mg/mL with acceptable precision and accuracy. No derivatization was required for these polar molecules. The retention times of the pravastatin, R-416 and the internal standard (R-1437) were 2.1, 2.5 and 3.9 min, respectively, with a total analysis time of 5 min. This method was validated and compared with the automated gas chromatography/negative ion chemical ionization mass spectrometry procedure.

RS-8359 is very rapidly absorbed, metabolized and distributed following oral dosing, with significant concentrations of both parent drug and its principal metabolite appearing in plasma within 15 min. Plasma levels were linearly related to doses of up to 300 mg, beyond which absorption was diminished, perhaps due to a saturation effect. Clearance of RS-8359 is mainly through the renal system as the metabolite, and is virtually complete within 24 h. The kinetic profile of the drug best fits a two-compartment model, and mean residence time and half-life (beta) of the drug support a twice a day regimen for extended use. During multiple dosing twice a day for up to 6 weeks, steady state plasma drug levels were achieved within 48 h and there was no evidence of significant accumulation.

Determination of the protein binding of troglitazone is difficult because of its high adsorption to filters and membranes and the instability of the stereoisomers. We attempted to assess the protein binding of four stereoisomers of troglitazone in the plasma and albumin from several species by the method using fluorescent probes. The inhibition constants (Ki) for the stereoisomers of troglitazone were obtained from the decreases in fluorescence intensity of dansylsarcosine caused by competitive inhibition. Each stereoisomer of troglitazone displaced dansylsarcosine, a typical specific fluorescent probe for the diazepam binding site on human serum albumin (HSA). The highest binding affinity for dansylsarcosine was observed with HSA (dissociation constant, Kd,1 = 0.5 microM), while it was lowest in the mouse (Kd,1 = 18 microM). The Ki values for KK and ddY mouse plasma and mouse and rat albumin were in the range 2-15 microM, and there were no large variations among stereoisomers, the maximum differences being twofold. For human plasma and albumin, the displacement could not be accounted for by a simple competitive inhibition. Comparison between unbound fraction (fu) values calculated from thus obtained Ki values and those of a mixture of the four stereoisomers determined by high-performance frontal analysis showed that the fu values obtained by fluorometric titration were higher, while the relative differences among the stereoisomers in terms of animal species and strain were comparable for the two methods. Small differences in protein binding among stereoisomers of troglitazone may not be the major reason for their stereoselective pharmacokinetics.

The dialysis clearance of active metabolites and the effective doses of temocapril and enalapril were studied in haemodialysis patients. Enalapril reduced blood pressure at dosages of 2.5 or 5 mg/day, and these dosages were lower than in patients with normal renal function (5 to 10 mg/day). In contrast, temocapril showed hypotensive effects at dosages of 2 or 4 mg/day, almost the same as in patients with normal renal function. The reason for this may be attributed to the different major excretory pathways of these drugs, i.e. enalapril via the kidneys and temocapril preferentially via both the liver and kidney. Dialysis clearance was determined after multiple oral doses. Enalaprilat showed a high clearance during dialysis (69.3 ± 24.2 ml/min), and this increased as the plasma drug concentration became high. On the other hand, temocaprilat clearance was rather low (7.7 ± 15.4 ml/min) and not dependent on the plasma drug concentration. These results indicate that temocapril can be used in haemodialysis patients without risk of significant accumulation, but its low haemodialysis clearance may require minimum dose adjustment.

Troglitazone, an oral antidiabetic agent, is an equal mixture of four stereoisomers involving two asymmetric centres. In the present study, the stereoselectivity of in vitro epimerization in plasma and organ homogenate and in vivo plasma disposition in the KK mouse, an animal model of non-insulin-dependent diabetes, was examined. In the incubation experiments at 37 °C, there was a fivefold to eightfold acceleration of epimerization at the 5 position of the thiazolidine ring in KK mouse plasma compared with that in buffer. However, no inversion at the 2 position of the chroman ring was observed. In addition, there was an approximately 1·3-fold difference in the epimerization rates among stereoisomers at the 2 position of the chroman ring. However, there were no differences in the values of the equilibrium constants of epimerization, and the ratio of epimerization among stereoisomers at the 5 position of thiazolidine ring was almost unity. The acceleration of epimerization is thought to be due to the high degree of protein binding because of the relationship between the initial epimerization rate and the dilution ratio of the plasma. Although acceleration of epimerization was also observed in the 20% homogenates of liver, kidney, and intestine of the KK mouse, the degree of stereoselectivity was lower than in plasma. The analysis of the plasma disposition after intravenous administration of troglitazone stereoisomers, using a kinetic model, indicated that the metabolic clearance in the liver showed a 2·5-fold maximum difference among stereoisomers and that the stereoselectivity of epimerization was low. ©1997 by John Wiley & Sons, Ltd.

Sites of the muscle relaxant action of CS-722 were investigated in rats. Doses injected intra-4th ventricularly (i.c.v.) or intrathecally (i.t.) were determined according to measurements of CS-722 concentration in the brain stem and the spinal cord after systemic administration. When administered i.c.v. (50 and 100 micrograms) or i.t. (200 and 400 micrograms), CS-722 reduced the radio frequency decerebrate rigidity, although the effect after i.c.v. injection was transient. These results indicate that CS-722 exerts its muscle relaxant action by affecting both the supraspinal structure and the spinal cord. Spinal reflexes were not affected by CS-722 injected i.c.v. It seems that muscle relaxation is not always accompanied by impairment of the spinal reflex.

Plasma concentration-time profiles of nimustine hydrochloride, 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosour ea hydrochloride (ACNU), in the mouse, rat, rabbit, and dog were determined by high-performance liquid chromatographic analysis. The pharmacokinetic parameters for these four animal species and previously reported clinical data were analyzed for investigation of interspecies correlation. Log-log plots of body weight (W; kg) vs total plasma clearance (CLtot,p; ml/min) and steady-state distribution volume (Vd,ss; l) for the four animal species were linear, with high correlation coefficients (r 0.996 for both parameters), despite the fact that the nonrenal clearance was greater than 97% in these species. Linear regression on the plots excluding human data yielded allometric equations (CLtot,p = 50.6 W0.957; Vd, ss = 1.29 W1.03) that were extrapolated to predict ACNU pharmacokinetic parameters in humans. For both parameters, however, there were 3-fold differences between the predicted and observed parametric values. To investigate these discrepancies, we measured serum protein binding of ACNU in these animal species and in humans. The values of CLtot,p and Vd,ss were converted into those of CLutot,p and Vd,uss, which correspond to the parameters for unbound ACNU. In this case, correlation coefficients of the log-log plots excluding human data (CLutot,p = 71.7 W0.891; Vd,uss = 1.82 W0.966) were also high (r greater than or equal to 0.991). The extrapolated values vs those observed in a 70-kg human were the following: CLutot,p, 3,160 vs 2,290 ml/min; Vd,uss, 110 vs 106 l. Thus, the animal data were successfully extrapolated to yield better predictions of human pharmacokinetic parameters if the analysis was based on the unbound plasma concentration of ACNU. In addition, the predicted plasma concentration-time profile for humans also showed good agreement with the observed ones. These results suggest the importance of measuring unbound fractions of drugs for more accurate prediction of human pharmacokinetic parameters by extrapolation of animal data to the human situation.

The glucuronide of a new oral antidiabetic agent, (+/-)-5-[4-(6-hydroxy-2,5,7,8-tetramethylchroman-2-yl- methoxy)benzyl]thiazolidine-2,4-dione (CS-045) (1), was synthesized to confirm the structure of a metabolite in monkeys (Macaca fascicularis) and to examine its antidiabetic activity. The glucuronide also had antidiabetic activity in KK-mice.

Plasma levels of levodopa, total dopamine, and residual amounts of levodopa and its metabolites at the administered site were analyzed following administration of single 100-mg doses of levodopa in solution into isolated segments of the duodenum, jejunum, and ileum of the dog. The largest area under the plasma concentration-time curve (AUC) of levodopa during the 1.0-hr study was obtained following administration in the duodenum, followed by the jejunum and ileum. In addition, the residual amounts of levodopa and its metabolites detected at the administration sites were: ileum, 23%; jejunum, 7% and duodenum, less than 1%. The largest AUC of total dopamine was obtained following administration in the jejunum, followed by the ileum and duodenum. This order was consistent with the order of levodopa decarboxylase enzyme activity reported previously. Therefore, it can be concluded that the major absorption site of levodopa in the intestine resides in the upper small intestine. Levodopa in 10-, 50-, and 100-mg doses was administered into isolated duodenal segments. The AUC of levodopa increased nonlinearly with increasing dose. Negligible amounts of both levodopa and its metabolites were observed in the segment at 1.0 hr after administration, indicating that the duodenal absorption of levodopa was not saturable within the dose range tested.

✓ The water-soluble nitrosourea compound ACNU is also lipid-soluble at normal physiological pH levels. It lacks toxic effects on vision that nitrosoureas occasionally produce following intra-arterial administration. In 28 cases of both primary and secondary malignant brain tumors, ACNU was administered at surgery or angiography by three different modes: intravenous injection in Group I (10 cases), intra-arterial injection via the carotid artery in Group II (11 cases), and intra-arterial injection via the carotid artery after opening the blood-brain barrier (BBB) by means of mannitol in Group III (seven cases). Tumor tissue and blood samples were taken serially at various time intervals after ACNU injection, and ACNU was measured by high-performance liquid chromatography. The time-concentration curve for ACNU was calculated in each case by the two- and one-compartment open models for determination of ACNU levels in blood and tissue, respectively. Pharmacokinetic parameters including biological half-life, blood and tissue levels (0-t minutes and 0-∞ minutes), total plasma clearance, and distribution volume of the β phase were compared. Statistical analysis of tissue ACNU levels at 0-t minutes revealed higher concentrations in Group III patients than in Groups II and I: levels in Group II were significantly higher than in Group I. Mean biological half-life was 30.3, 23.0, and 38.5 minutes in Groups I, II, and III, respectively. Levels of ACNU were significantly increased in tumor tissue as well as in peritumoral tissue in one Group III patient with multiple metastatic anaplastic adenocarcinoma. In this series, treatment of malignant brain tumor by intra-arterial administration of ACNU produced significantly higher tissue levels of ACNU than did the systemic intravenous route.

The relationship between the dose of levodopa and its pharmacokinetic behavior following intravenous and oral administration was investigated in dogs and parkinsonian patients. Six beagle dogs received single doses of 2.4, 4.8, and 9.6 mg of levodopa/kg iv and single doses of 4.8, 9.6, and 19.2 mg of levodopa/kg po in a crossover fashion on separate occasions. Three parkinsonian patients received single oral doses of approximately 3.8, 7.7, and 15.4 mg of levodopa/kg in a crossover test. Plasma samples were analyzed for intact levodopa and total dopamine. The relationship between the area under the plasma concentration-time curve (AUC) of levodopa and the intravenous dose to dogs was linear. However, in both dogs and patients, the relationship after oral dosing was nonlinear, with the relative AUC increasing with increasing dose. Therefore, the pharmacokinetic behavior of levodopa after oral administration to dogs and patients was dose dependent.

The degradation kinetics of pivaloyloxymethyl (POM) esters of cephalosporins in phosphate buffer solution (pH 6-8) were investigated. The degradation of the starting delta 3 cephalosporin ester proceeded mainly via isomerization to the delta 2 ester and subsequent hydrolysis to the delta 2 acid. Hydrolysis to the delta 3 acid (the parent acid) was very slow. Analysis of the rate constants indicated that the isomerization rate k12 was approximately equal to the apparent degradation rate of the delta 3 ester kdeg, and slower than the hydrolysis rate of the delta 2 ester k24. The isomerization process to the delta 2 ester was found to be the rate-determining step in the degradation of cephalosporin esters. The substituent at the C-3 position of the cephalosporins affected the degradation kinetics. The degradation was accelerated by increase of pH, buffer concentration and added protein.

Oral acute toxicity of medium chain glyceride (MCG) was studied in mice and rats. In mice and rats, clinical signs such as irregular respiration, laxity of movement, staggering gait and loss of righting reflex appeared after single oral administration of MCG at a relatively large dose. The LD50 values determined in male and female mice were 26.9 and 28.5 ml/kg, and in male and female rats were 27.4 and 26.7 ml/kg, respectively. In order to evaluate the biological safety of MCG suppository of cefmetazole sodium (CMZ), its local irritation on the mucous membrane was studied. Primary eye irritation of MCG suppository of CMZ was studied in rabbits. Although mild irritation was seen in conjunctivae, no remarkable changes were observed in cornea and iris. Furthermore, primary effect of MCG suppository of CMZ on the rectal mucous membrane was studied macro- and micro-scopically. It was observed that remarkable histological changes of rectal mucous membrane by MCG suppository of CMZ were not observed in all animals used.

The distribution of orally and intravenously administered 14C-oxazolam was studied in mice by means of whole-body autoradiography and in rats by scintillation counting of the organs and tissues. The radioactivity was found to be widely distributed in various tissues including the brain at 30 min after oral administration, reached the maximum levels within 1 hr and thereafter declined rather rapidly. The distribution patterns were similar for mice and rats, except that the brain uptake of the drug was appreciably higher in mice than in rats. A high affinity of oxazolam to the brain tissue was demonstrated by an extremely high and rapid uptake of radioactivity by the brain after intravenous injection in mice. The brain level reached its maximum at about 1 min after the injection and thereafter fell off rapidly, some retention of radioactivity being observed in the white matter of the brain-stem and in the trigeminal nerve. Autoradiographic studies in pregnant mice demonstrated that there is a slow and only a slight penetration of radioactivity through the placenta. A comparison of the excretion patterns of oxazolam after oral administration in mice, rats, dogs and man revealed that in mice and rats the excretion in the feces, mostly derived from the biliary excretion, was more important than that in the urine, while in dogs a larger part was excreted in the urine and in man the most part (ca. 80% of the dose) in the urine.

Various classes of transient derivatives of L-Dopa have been synthesized, systematically protecting one or more of the main sites of metabolism in the molecule: the carboxy function, the amino, and/or the catechol system. The derivatives studied include carboxy esters, phenol esters, amides, peptides, and various combinations of these functions. A number of these derivatives effectively prevent the metabolism of L-Dopa prior to and/or during the absorption process, resulting in a significantly better bioavailability of the drug. In vivo studies using dogs showed up to 2.5-fold increase in L-Dopa blood levels. The metabolism as well as toxicity aspects of the prodrugs is also discussed.

To estimate the absolute bioavailability of oral levodopa, plasma concentrations and urinary excretion of levodopa and its metabolites were determined in beagle dogs and in parkinsonian patients after intravenous and oral drug administration. The absolute bioavailability of orally administered levodopa was estimated to be about 35% in both dogs and patients; however, the total amount absorbed of intact drug and levodopa metabolites was estimated to be 80--90% of the administered dose. Due to the similarities of the pharmacokinetic characteristics of levodopa found in beagle dogs and in humans, beagle dogs can serve as a model to study bioavailability, absorption, and metabolic mechanisms.

A new dosage form of levodopa, which has the characteristics of loading high concentrations of levodopa at the upper part of the intestine, has been developed to improve its bioavailability. It is shown that an effervescent tablet formulation, coated with hydroxypropyl methylcellulose phthalate (carboxybenzoyl radical content: 20–24%) as the enteric material, is suitable for the purpose of dissolution. This was confirmed from animal experiments, which showed that tablets of this composition disintegrate instantly on reaching the upper part of the intestine. This tablet was considered appropriate for the bioavailability tests described in this paper.

The promoting effects of medium chain glyceride (MCG) on the rectal absorption of β-lactam antibiotics were compared among various experimental animals (such as rats, rabbits and dogs). The plasma levels of cefmetazole (CMZ) after rectal administration, when MCG was used as the vehicle, significantly increased in all animals, but the bioavailability of CMZ was greatly varied among the animal species ; the bioavailability of CMZ in dogs was apparently less than those in other animals (rats=rabbits > dogs). However, in dogs, the promoting effect of MCG on the rectal absorption of CMZ increased by addition of nonionic surfactants such as ether-type (Brij 30[○!R] and Brij 35[○!R]) and ester type (Nikkol MYL-10[○!R]). And the promoting effect of surfactants in the MCG vehicle is not always correlated with blood hemolysis, suggesting contribution of other physicochemical or biological factors.

The effect of medium chain glyceride (MCG) on the intestinal absorption of cefmetazole sodium (CMZ) was investigated in rats and dogs. In rats, MCG containing glyceryl mono-, di- and tri-caprylate enhanced the intestinal absorption of CMZ after intraduodenal administration, though the promoting effect of MCG was less than that after rectal administration. The promoting effect of MCG was found to be mainly due to glycerylmonocaprylate and dependent on the dosage of MCG. The plasma CMZ levels after intraduodenal administration as MCG solution tended to be slightly higher than those observed after administration as MCG emulsion, though the differences were found to be statistically insignificant. Moreover, the intestinal absorption of CMZ after intraduodenal administration as MCG emulsion was decreased significantly by increasing the amount of water in the emulsion. The promoting effect of MCG in dogs was more clearly demonstrated in the lower intestine than in the upper intestine. Furthermore, the oral bioavailability of pharmaceutical formulations of CMZ was also investigated in dogs. When enteric coated capsules filled with MCG solution were administered to dogs, the bioavailability of CMZ was enhanced significantly.

Various classes of transient derivatives of L-Dopa have been synthesized, systematically protecting one or more of the main sites of metabolism in the molecule: the carboxy function, the amino, and/or the catechol system. The derivatives studied include carboxy esters, phenol esters, amides, peptides, and various combinations of these functions. A number of these derivatives effectively prevent the metabolism of L-Dopa prior to and/or during the absorption process, resulting in a significantly better bioavailability of the drug. In vivo studies using dogs showed up to 2.5-fold increase in L-Dopa blood levels. The metabolism as well as toxicity aspects of the prodrugs is also discussed.

The mechanisms of the promoting effect of medium chain glyceride (MCG) containing glyceryl mono-, di- and tri-caprylate on rectal absorption of water soluble drugs were investigated. It was found that the solubility behavior of the drugs in mucosal fluids on the surface of the membrane are critical factor for the enhanced rectal absorption. Moreover, the drugs to be readily absorbed from MCG base may be ones of low partition coefficients to MCG phase as well as high solubility in water. And it was found that MCG can't be absorbed from the rectum, different from oral administration, suggesting an interaction of MCG with absorption membrane, rather than the carrier effect of MCG itself. Furthermore, from the results in the pretreatment experiments and additional administration of MCG alone, it was suggested that the interactions of MCG with the membrane components, as well as the induction of biological or physiological changes, may be at least partly responsible for the promoting effect of MCG.

The effect of medium chain glyceride on the rectal absorption of cefmetazole sodium is investigated using an in situ experiment in rats. Each glyceride component of medium chain glyceride was separated using a high-performance liquid chromatographic method. The promoting effect of medium chain glyceride was found to be mainly due to glycerylmonocaprylate and dependent on the concentration of glycerylmonocaprylate. When cefmetazole sodium in medium chain glyceride solution was administered into the rectal lumen of rats, rapid absorption of the drug was observed leading to a residual amount of about 45% at 15 min after administration. The promoting effect of medium chain glyceride was found to be more effective in the rectum than in the small intestine.