Is the inversion from R- to S-ketoprofen concentration dependent? Investigations in rats in vivo and in vitro

The effects of dose on the pharmacokinetics of ketoprofen (KT) enantiomers were investigated in rats in vivo and in hepatoma cells in continuous culture in vitro following administration of the optically pure enantiomers and the racemate of KT. With the exception of AUC (area under the curve) no pharmacokinetic differences could be found following i.v. administration of various doses of KT enantiomers (2.5, 5 and 10 mg/kg) and of racemic KT (5, 10 and 20 mg/kg) and between single enantiomer and racemate administration in rats in vivo. Independent of the dose administered the fraction inverted was about 66%. In line with the findings in vivo good correlation between incubation concentration and AUC of R- and S-KT was found in the hepatoma cells in vitro. The ratios of AUC(S)/AUC(R) were not significantly affected by concentration after R-KT (2.5-20 micrograms/mL) and racemate incubation (5-40 micrograms/mL) in the concentration ranges investigated. However, unlike in rats in vivo enhanced inversion was observed following racemate as compared to single enantiomer incubation in vitro.     

In vitro ammonia utilization and urea synthesis by rat liver after portacaval shunt

AIMS: To investigate the transplacental distribution of salbutamol enantiomers after administration of racemate to women prior to Caesarian section. METHODS: Five women about to undergo elective Caesarian section were administered a single 0.25 mg bolus intravenous dose of (R,S)-salbutamol. The time from drug administration to delivery was different for each woman (27-105 min). Maternal and foetal umbilical cord venous blood samples were collected immediately after delivery and the plasma fraction analysed for salbutamol enantiomer concentrations by enantioselective high pressure liquid chromatography. RESULTS: The concentrations (mean +/- s.d.) of the active (R) enantiomer of salbutamol in cord and maternal plasma were 0.46 +/- 0.35 and 0.89 +/- 0.50 ng ml-1, respectively, and the difference was statistically significant (95% confidence interval (CI) of the difference: 0.12-0.74 ng ml-1). The corresponding concentrations of the (S) enantiomer of 0.92 +/- 0.45 and 1.11 +/- 0.67 ng ml-1, respectively, were not significantly different (95% CI of the difference -0.08-0.48 ng ml-1). The ratio of (R):(S) in cord plasma was significantly less than that in maternal plasma (P=0.016). CONCLUSIONS: Transplacental distribution of salbutamol enantiomers at Caesarian section after prior administration of racemate to mothers leads to concentrations in cord plasma that are significantly less for the active (R) enantiomer and not significantly different for the (S) enantiomer than in maternal plasma presumably due to enantioselective placental-foetal metabolism.     

Comparative repellency of commercial formulations of deet, permethrin and citronellal against the mosquito Aedes aegypti, using a collagen membrane technique compared with human arm tests

The plasma concentrations and urinary excretions of bisoprolol enantiomers in four Japanese male healthy volunteers after a single oral administration of 20 mg of racemic bisoprolol were evaluated. The AUC(infinity) and elimination half-life of (S)-(-)-bisoprolol were slightly larger than those of (R)-(+)-bisoprolol in all subjects. The metabolic clearance of (R)-(+)-bisoprolol was significantly (P < 0.05) larger than that of (S)-(-)-bisoprolol (S/R ratio: 0.79+/-0.03), although the difference was small. In contrast, no stereoselective in vitro protein binding of bisoprolol in human plasma was found. An in vitro metabolic study using recombinant human cytochrome P450 (CYP) isoforms indicated that oxidation of both bisoprolol enantiomers was catalyzed by the two isoforms, CYP2D6 and CYP3A4. CYP2D6 metabolized bisoprolol stereoselectively (R > S), whereas the metabolism of bisoprolol by CYP3A4 was not stereoselective. The S/R ratio of the mean clearance due to renal tubular secretion was 0.68, indicating a moderate degree of stereoselective renal tubular secretion. These findings taken together suggest that the small differences in the pharmacokinetics between (S)-(-)- and (R)-(+)-bisoprolol are mainly due to the stereoselectivity in the intrinsic metabolic clearance by CYP2D6 and renal tubular secretion.     

Integrated physical and transcript map of 5q31.3-qter

The disposition of S-2-[4-(3-methyl-2-thienyl)phenyl]propionic acid (CAS 155680-07-2, S-MTPPA, code: M-5011) was studied after oral administration to rats, dogs and monkeys using the 14C-labeled drug. After oral dosing, S-MTPPA was well absorbed from the gastrointestinal tract, to the extent of 97.7% in rats. The concentration of S-MTPPA in rat plasma reached a peak (Cmax: 13.07 micrograms/ml) at 15 min (tmax) after dosing and declined with a half-life (t1/2) of 2.5 h. The values of the parameters tmax, Cmax and t1/2 for dogs were 30 min, 26.2 micrograms/ml and 7.0 h, and those for monkeys were 15 min, 12.8 micrograms/ml and 3.0 h, respectively. The radioactivity was widely distributed in tissues and almost completely excreted in urine and feces within 48 h after oral administration to rats. The excretion of radioactivity in bile, urine and feces within 48 h after oral administration of 14C-S-MTPPA to bile duct-cannulated rats amounted to 75.0, 18.6 and 1.4% of the dose, respectively. The drug was metabolized mainly by oxidation of the thiophenyl moiety and by glucuronidation of the carboxyl group in rats and monkeys. The major urinary and fecal metabolite in dogs was identified as the taurine conjugate of MTPPA.     

Oral rehydration of infants with hypernatremic dehydration due to acute gastroenteritis

A stereoselective and sensitive method for the determination of the enantiomers of felodipine, a dihydropyridine calcium antagonist, has been developed and the pharmacokinetic profiles of the enantiomers comparatively studied after oral administration to dogs and humans. D6-Felodipine, the internal standard, was added to the plasma, extracted with a solvent and then optically resolved into S(-) and R(+) enantiomers on a high performance liquid chromatographic Chiralcel OJ column. Each enantiomer in the effluent was analysed by capillary column gas chromatography/positive ion electron impact mass spectrometry. After oral administration of the felodipine racemate, the Tmax and t1/2 values hardly differed between the two enantiomers in dogs and humans. The Cmax and AUC0-24 h values of the S(-) enantiomer were slightly higher than those of the R(+) enantiomer in humans but the difference between the enantiomers was not significant. These results suggested that there is no large difference in the absorption, distribution and elimination of felodipine enantiomers after oral administration of the racemate in either dog or human.     

Effects of phenobarbital on stereoselective metabolism of ifosfamide in rats

Plasma and urinary levels of ifosfamide (IF) enantiomers and their metabolites 2-dechloroethylifosfamide, 3-dechloroethylifosfamide, 4-hydroxyifosfamide, and isophosphoramide mustard were determined for control and phenobarbital-treated male Sprague-Dawley rats by using pseudoracemates and GC/MS and stable-isotope dilution analytical methods. For the control rats, the mean AUC for (S)-IF in plasma was greater than that for (R)-IF (R/S AUC ratio, 0.78) and the mean half-life of 41.8 min for (S)-IF was slightly longer than that of 34.3 min for (R)-IF. Phenobarbital pretreatment significantly decreased the AUC values for (R)-IF and (S)-IF, to 21 and 30% of the control values, respectively, and shortened plasma half-lives for both enantiomers [half-life for (R)-IF, 19.8 min; half-life for (S)-IF, 19.4 min]. The urinary excretion values for (R)-IF and (S)-IF were decreased to 41 and 30% of the control values, respectively. The overall amounts of the metabolites in urine were concomitantly increased. Additionally, there were significant reversals in both the R/S AUC ratio and the urinary excretion of 3-dechloroethylifosfamide. Moreover, the enantioselectivity for the generation of 4-hydroxyifosfamide and isophosphoramide mustard disappeared after phenobarbital treatment. These results strongly suggested that the 4-hydroxylation and dechloroethylation of IF enantiomers were mediated by different P450 isozymes or the same isozyme with different stereochemical selectivities.     

The enantiomers of phenprocoumon: pharmacodynamic and pharmacokinetic studies

The pharmacodynamics and pharmacokinetics of the optical enantiomers of phenprocoumon were studied in 5 normal subjects and compared to the racemic mixture. Each subject received a single oral dose of 0.6 mg/kg of racemic, S(-), and R(+) phenprocoumon. S(-) phenprocoumon was 1.6 to 2.6 times as a potent as R(+) phenprocoumon when the area under the effect/time curve was used to quantify the total anticoagulant effect per dose. Comparing the plasma concentrations that elicited the same anticoagulant effect, S(-) phenprocoumon was 1.5 to 2.5 times as potent as R(+) phenprocoumon. The anticoagulant activity of the racemic mixture was between that of the enantiomers. There was no distinct difference in the rate of elimination between the enantiomers. The apparent volume of distribution and the plasma clearance for S(-) phenprocoumon were less than those for R(+) phenprocoumon. When the binding of the enantiomers to human serum albumin was compared, S(-) phenprocoumon was more highly bound than R(+) phenprocoumon. The protein binding of racemic phenprocoumon was between that of the enantiomers. The results show that S(-) phenprocoumon is more potent anticoagulant than R(+) phenprocoumon and that the pharmacokinetic differences between the enantiomers are due mainly to differences in their distribution.     

Evidence of absorption rate dependency of ibuprofen inversion in the rat

Ibuprofen (IB) is a chiral 2-arylpropionic acid derivative used as a nonsteroidal antiinflammatory drug (NSAID). It undergoes substantial R to S chiral inversion in humans and rats. In addition to systemic inversion, presystemic chiral inversion has been suggested for IB in humans but only after administration of formulations with slow absorption rates. In search for a suitable animal model, the absorption rate dependency of the extent of inversion was examined in male Sprague-Dawley rats given 20 mg/kg of racemic IB in aqueous solution (Tmax, 0.6 h), suspension (Tmax, 1 h) or as sustained release granules (Tmax, 2.3 h). In addition, (R)-IB (5 mg/liter) was incubated in the presence of everted rat gut segments in an organ bath at 37 degrees. After sustained release granules, the S:R AUC ratios (7.3 +/- 1.5) were significantly higher than suspension (3.6 +/- 1.1) and solution (3.5 +/- 0.2). Accordingly, AUCS and AUCR, as percent of the total AUC (S+R), significantly increased and decreased, respectively, after administration of the sustained released granules as compared with the solution and suspension. A significant positive linear correlation was found between the S:R AUC ratios and the corresponding Tmax for (R)-IB (r = 0.82). In vitro, (R)-IB was inverted by everted jejunum (12.2 +/- 1.6%), ileum (14.2 +/- 2.0%), and colon (4.4 +/- 0.6%) segments. IB was also glucuronidated in the presence of the intestinal segments. Therefore, similar to earlier observations made in humans, in the rat, the S:R AUC ratio was positively and significantly correlated with the absorption rate from the dosage form.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stereoselective metabolism, pharmacokinetics and biliary elimination of phenylethylhydantoin (Nirvanol) in the dog

The influence of stereoisomerism on pharmacokinetics and rates of hepatic drug metabolism was investigated in four dogs using the enantiomers of phenylethylhydantoin (PEH) as model substances. After single i.v. administration of 98 micromoles of the pure enantiomers per kg b.wt., concentrations were measured by gas-liquid chromatography. The l-form exhibited a longer plasma half-life (23.3 +/- S.E. 1.0 hour) than the d-form (16.3 +/- 1.0 hour, P less than .005). Volumes of distribution and renal clearances were practically identical. The differences in plasma half-lives of PEH were explained by stereoselectivity of hepatic hydroxylation: an approximately 10-fold differences was found in urinary excretion of their major metabolities, d- and l-hydroxyphenylethylhydantoin (HPEH). Furthermore, in bile 7.3 +/- 1.6 mumol of of d-HPEH were eliminated within the first 6 hours, whereas l-HPEH could not be detected. The preference in biliary output of d- compared with l-PEH is consistent with the idea that both hepatic uptake and microsomal hydroxylation of PEH contribute to the high degree of stereoselectivity. In view of similar extrahepatic, but different metabolic behavior of these enantiomers, they represent an interesting research tool for in vivo studies of drug metabolism: in otherwise identical conditions, two different rates of PEH hydroxylation may be studied.     

Mechanism of biliary lipid secretion in the rat: a role for bile acid-independent bile flow?

Bile acid-induced lipid secretion was compared in unanesthetized normal control and Groningen Yellow Wistar rats during variations in endogenous bile acid output. Groningen Yellow rats express a genetic defect in the biliary secretion of various organic anions. During a 5-hr period after interruption of the enterohepatic circulation, bile acid secretion decreased from 36.4 +/- 1.8 to 1.9 +/- 0.3 mumol per 30 min in normal control rats and from 37.1 +/- 2.8 to 1.8 +/- 0.2 mumol per 30 min in Groningen Yellow rats, respectively (mean +/- S.E.M., n = 5). The relationship between bile acid secretion and bile flow showed similar slopes (normal control, 8.74 +/- 0.44 microliter/mumol and Groningen Yellow rats, 7.71 +/- 0.42 microliter/mumol) but different y-intercepts (normal control, 243 +/- 8 and Groningen Yellow, 127 +/- 4 microliters per 30 min; p < 0.001), corresponding to a 47% reduction of the bile acid-independent fraction of bile flow in Groningen Yellow rats. During the course of the experiment, the ratio of lipids (phospholipids plus cholesterol) to bile acids increased in both strains more than threefold but was permanently higher in Groningen Yellow than in normal control rats (p = 0.035), implying that Groningen Yellow rats continuously secreted more lipid per bile acid. No differences in bile acid pool composition or in bile canalicular membrane composition and fluidity between the two strains were detected. The results indicate that apart from previously demonstrated factors (bile acid concentration, bile acid composition and hydrophilic organic anion concentration in bile), another parameter affects the efficacy of bile acids to induce biliary lipid secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of the enantiomers of verapamil after intravenous and oral administration of racemic verapamil in a rat model

Verapamil is a chiral calcium channel blocking drug which is useful clinically as the racemate in treating hypertension and arrhythmia. The published pharmacokinetic data for verapamil enantiomers in the rat model are limited. Utilizing a stereospecific high-performance liquid chromatographic (HPLC) assay, the enantiomeric disposition of verapamil is reported after intravenous (1.0 mg kg-1) and oral (10 mg kg-1) administration of racemic verapamil to the rat model. After intravenous administration the systemic clearance of R-verapamil was significantly greater than that of S-verapamil; 34.9 +/- 7 against 23.7 +/- 3.7 mL min-1 kg-1 (mean +/- SD), respectively. After oral administration, the clearance of R-verapamil was significantly greater than that of S-verapamil, 889 +/- 294 against 351 +/- 109 mL min-1 kg-1, respectively. The apparent oral bioavailability of S-verapamil was greater than that of R-verapamil, 0.074 +/- 0.031 against 0.041 +/- 0.011, respectively. These data suggest that the disposition of verapamil in the rat is stereoselective; verapamil undergoes extensive stereoselective first-pass clearance after oral administration and the direction of stereoselectivity in plasma is opposite to that observed in the human.     

Moment analysis of stereoselective enterohepatic circulation and unidirectional chiral inversion of ketoprofen enantiomers in rat

The stereoselective enterohepatic circulation (EHC) and the synchronous chiral inversion of ketoprofen enantiomer in rat were evaluated by moment analysis based on the recirculatory concept. (R)-(-)- and (S)-(+)-ketoprofen were independently administered into rats, and the plasma and bile concentrations of both enantiomers were determined by a column-switching HPLC. (S)-Ketoprofen was generated by the chiral inversion from (R)-ketoprofen, whereas (R)-ketoprofen was not generated from (S)-ketoprofen. Within 30 min after intravenous administrations, the plasma time courses of R- and S-enantiomers were almost the same between rats with laparotomy and those with bile-duct cannula. After 30 min, the plasma concentrations in rats with laparotomy were significantly higher than those in rats with bile-duct cannula. The Laplace-transformed equations for stereoselective EHC and the synchronous chiral inversion were derived by means of the transfer function method on the basis of the recirculatory theory. The global moments (AUC and MRT) which were derived directly from the transformed equations were related to the local moments for the single EHC. The recirculation ratios of (R)- and (S)-ketoprofen for the single EHC were estimated to be 15.4% and 63.6%, respectively. The absorption ratios of (R)- and (S)-ketoprofen for the absorption process from the gastrointestinal tract into the systemic circulation were 87.0% and 83.8%, respectively. The biliary excretion rations of (R)- and (S)-ketoprofen for the disposition process through the systemic circulation into the bile were 17.7% and 75.8%, respectively. The chiral inversion ratio from (R)-ketoprofen into (S)-ketoprofen was 59.5%. The complicated disposition of ketoprofen, i.e., the simultaneous EHC and chiral inversion, was able to be analyzed by a moment method in a simple way.     

Tissue distribution and biotransformation of zopolrestat, an aldose reductase inhibitor, in rats

Zopolrestat (Alond) is a new drug that is being evaluated as an aldose reductase inhibitor for the treatment of diabetic complications. 14C-labeled zopolrestat was orally administered to rats for a tissue distribution study and a bile duct cannulation metabolism study. Tissue samples from the distribution study were analyzed by complete oxidation and liquid scintillation counting. Urine and bile samples from the bile duct cannulation study were analyzed by microbore HPLC, with simultaneous radioactivity monitoring and atmospheric pressure ionization tandem mass spectrometry. The mass balance in the distribution study demonstrated that the greatest exposure (AUC0-infinity) occurred in the liver, followed by the ileum and large intestine. The time of maximal plasma concentrations for nearly all tissues was 4 hr after the dose, and the half-life of radioactivity in most tissues (8-10 hr) was similar to the half-life in plasma. For the bile duct-cannulated rat study, most of the radioactivity was recovered in the bile, indicating that biliary excretion is a major route of elimination of zopolrestat and its metabolites in rats. Numerous oxidative metabolites, as well as phase II conjugates, were identified in the bile and urine samples. Acyl glucuronides of zopolrestat and unchanged drug accounted for >85% of biliary radioactivity, whereas unchanged drug and degradation products of glutathione conjugates were identified as the major urinary metabolites.     

Macromolecular intravenous contrast agent for MR lymphography: characterization and efficacy studies

PURPOSE: To determine the pharmacokinetic and magnetic resonance (MR) imaging properties of diethylenetriaminepentaacetic acid (DTPA) conjugated with a polyglucose-associated macrocomplex (PGM), which accumulates in lymph nodes. MATERIALS AND METHODS: In 124 normal and 20 tumor-bearing rats, Gd-DTPA PGM was administered intravenously in doses of 2, 10, 20 mumol gadolinium per kilogram of tissue. RESULTS: Mean blood half-life was 2 hours. Maximum accumulation in peripheral (33.0% injected dose [ID]/g +/- 16.2 [standard deviation]) and central lymph nodes (63.2% ID/g +/- 16.5) was observed within 24 hours after administration. The optimum dose range was 10-20 mumol Gd/kg in rats. At 24 hours after administration of 20 mumol Gd/kg, the signal-to-noise ratio increased from 30.9 +/- 0.4 to 83.2 +/- 5.2 in normal lymph nodes (P < .001). Differentiation between normal and metastatic lymph nodes was improved. CONCLUSION: When labeled with Gd-DTPA, the PGM-based graft copolymer significantly increases signal intensity at MR imaging of normal but not metastatic lymph nodes without causing distortion artifacts.     

Orally active inhibitors of human leukocyte elastase. II. Disposition of L-694,458 in rats and rhesus monkeys

The disposition of L-694,458, a potent monocyclic beta-lactam inhibitor of human leukocyte elastase, was studied in male Sprague-Dawley rats and rhesus monkeys. After iv dosing, L-694,458 exhibited similar pharmacokinetic parameters in rats and rhesus monkeys. The mean values for its plasma clearance, terminal half-life, and volume of distribution at steady state were 27 ml/min/kg, 1.8 hr, and 4.0 liters/kg in rats and 34 ml/min/kg, 2.3 hr, and 5 liters/kg in rhesus monkeys. The bioavailability of a 10 mg/kg oral dose was higher in rats (65%) than in rhesus monkeys (39%). In both species, concentrations of L-694,458 in plasma increased more than proportionally when the oral dose was increased from 10 mg/kg to 40 mg/kg. In monkeys a protracted plasma concentration-time profile was observed at 40 mg/kg, characterized by a delayed T(max) (8-24 hr) and a long terminal half-life (6 hr). [3H]L-694,458 was well absorbed after oral dosing to rats at 10 mg/kg, as indicated by the high recovery of radioactivity in bile (83%) and urine (6%) of bile duct-cannulated rats. Only approximately 5% or less of the radioactivity in bile, urine, and feces was a result of intact L-694,458, indicating that the compound was being eliminated by metabolism, followed by excretion of the metabolites in feces, via bile. Demethylenation of the methylenedioxyphenyl group resulting in the catechol was the primary metabolic pathway in human and rhesus monkey liver microsomes. In rat liver microsomes, the major metabolite was the N-oxide of the methyl-substituted piperazine nitrogen. In rats dosed iv and orally with [3H]L-694,458, concentrations of radioactivity were highest in the lung (the primary target tissue), adrenals, and liver. L-694,458 was unstable in rat blood and plasma, degrading via a pathway believed to be catalyzed by B-esterases and to involve cleavage of the beta-lactam ring and loss of the methylpiperazine phenoxy group. In vitro studies indicated that in human liver, L-694,458 was metabolized by CYP3A and 2C isozymes, and in both monkey and human liver microsomes the compound acted as an inhibitor of testosterone 6beta-hydroxylation.     

Effect of experimental diabetes mellitus and arthritis on the pharmacokinetics of hydroxychloroquine enantiomers in rats

PURPOSE: To study the effect of experimental diabetes and arthritis on the pharmacokinetics of hydroxychloroquine (HCQ) enantiomers in rats. METHODS: The pharmacokinetic studies were carried out following administration of 40 mg/kg of racemic HCQ to diabetic, insulin-treated diabetic, adjuvant arthritic and control rats. RESULTS: Renal (70% and 62% for R- and S-HCQ, respectively) and non-renal clearance (100% and 145% for R- and S-HCQ, respectively) of HCQ enantiomers were significantly increased in diabetic rats. Diabetes-induced alterations in the disposition of HCQ were reversed by insulin treatment. In arthritic rats, systemic clearance (CL) of HCQ enantiomers was significantly reduced (1.05 +/- 0.15 and 1.3 +/- 0.19 l/h/kg for R- and S-HCQ, respectively) compared to controls (1.69 +/- 0.32 and 1.93 +/- 0.34 l/h/kg for R- and S-HCQ, respectively). The fraction unbound of the R- and S-HCQ were 49.4% and 50.5% lower in platelet rich plasma of arthritic rats compared to healthy rats. Increased blood concentrations of HCQ enantiomers in arthritic rats were significantly related to the degree of inflammation. CONCLUSIONS: Diabetes significantly increased the CL of both R- and S-HCQ by increasing renal and non-renal clearance. Arthritis caused a significant decrease in CL of HCQ enantiomers through increased binding and a decreased intrinsic clearance. The effect of the diseases on the pharmacokinetics of HCQ, however, was not stereoselective.     

Effect of androgen administration during puberty on hepatic CYP2C11, CYP3A, and CYP2A1 expression in adult female rats

This biochemical and pharmacokinetic investigation was undertaken to evaluate the effects of androgen administration during puberty on sex-dependent cytochrome P450 (CYP or P450) enzyme expression in adult female rats. Hepatic testosterone 2alpha-hydroxylase activity and CYP2C11 and CYP3A protein levels were elevated in prepubertally ovariectomized rats injected subcutaneously with testosterone enanthate at 35-49 days of age and killed 41 days after discontinuation of treatment. In contrast, testosterone 6beta- and 7alpha-hydroxylase activities and CYP2A1 protein content were not affected. The increase in CYP2C11 and CYP3A was likely not due to circulating testosterone because plasma testosterone was undetectable. The calculated elimination half-life was 51 +/- 6 hr (mean +/- SE) after testosterone enanthate administration. By 80 days after treatment, CYP2C11 and CYP3A levels were no longer increased. To determine if CYP2C11 expression was responsive to a more periodic pattern of androgen release, ovariectomized rats were injected subcutaneously once or twice daily with unesterified testosterone (elimination half-life was 2.0 +/- 0.3 hr, mean +/- SE). Once- or twice-daily dosing (5 or 2.5 micromol/kg/injection, respectively) during days 35-49 of age did not increase the mean CYP2C11 expression in 90-day-old female rats, although testosterone 2alpha-hydroxylase activity and CYP2C11 protein content were elevated in three of the eight rats injected twice daily. Neither dosing regimen increased CYP3A or decreased CYP2A1 expression. In summary, the results indicate that treatment with testosterone enanthate during puberty resulted in a prolonged but reversible increase in hepatic expression of CYP2C11 and CYP3A.     

Characterization of Aspergillus nidulans peroxisomes by immunoelectron microscopy

We investigated the possible role of enterohepatic recirculation in prolongation of the half-life of elimination for Adriamycin, a commonly prescribed anticancer agent. We sought to determine whether enterohepatic recirculation of Adriamycin and its metabolites occurs using a linked-rat model. Two rats, a donor and a receiver, were linked via a catheter from the bile duct of the donor rat to the duodenum of the receiver. Control experiments were conducted with intact rats (without a bile duct cannula, control A) in order to estimate the half-life of elimination and with bile duct-cannulated rats (control B) to determine the amounts of Adriamycin and its metabolites in the bile. [14C-14]-Adriamycin was injected intravenously via the femoral vein to control A, control B and donor rats. The biological half-life of Adriamycin in the intact rats (control A, 10 h) was significantly higher than in the bile-duct-cannulated rats (control B, 4 h). The cumulative amount of Adriamycin and its metabolites excreted in the urine of the control A rats was also greater than from control B rats, indicating higher levels of the drug in their systemic circulation. Biological samples (bile, urine, plasma, blood cells and the major organs heart, liver and kidney) of the receivers contained significant amounts of Adriamycin and its metabolites. The total radioactivity recovered in the bile of the receivers accounted for 0.1% to 8% of the Adriamycin dose that was administered to the donors. Adriamycin and its metabolites appeared there only after a lag time that was consistent among all the receivers. Doxorubicinol aglycone was the major metabolite found in the bile and urine of the receivers. Low but constant levels of radioactivity were also detected in the plasma and blood cells of the receivers. The presence of unchanged Adriamycin in the bile and urine of the receivers suggested absorption of the parent drug from the intestine of the receivers. Overall, we estimated that about 22% of the dose injected to the donors was absorbed from the intestine of the receivers. Taken together, these findings clearly demonstrate a significant role for enterohepatic recirculation of Adriamycin and its metabolites, which may contribute to the ability of these compounds to induce cumulative cardiac damage and/or to increase the efficacy of Adriamycin.     

Stereoselective HPLC bioanalysis of atenolol enantiomers in plasma: application to a comparative human pharmacokinetic study

An enantioselective HPLC bioassay has been developed relying on extraction of (R)- and (S)-atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1-butanol followed by an achiral derivatization of the drug with phosgene leading to (R)- and (S)-oxazolidine-2-one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)-diaminocyclohexane-dinitrobenzoyl chiral stationary phase [(R,R)-DACH-DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0.5 ng for (R)- and 0.6 ng for (S)-atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross-over, double-blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)-, 50 mg (R)-, and 50 mg (S)-atenolol. AUC0-24 and Cmax values of (R)-atenolol were slightly but significant higher than those of (S)-atenolol. The R/S ratios were 1.09 for AUC(R)/AUC(S) and 1.03 for Cmax (R)/Cmax(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no difference between AUC, Cmax, and t1/2 values of each enantiomer, whether they were administered as single enantiomers or in the form of its racemic mixture.     

Antinociceptive actions of R(-)-flurbiprofen--a non-cyclooxygenase inhibiting 2-arylpropionic acid--in rats

Intraperitoneal administration of R(-)- and S(+)-flurbiprofen resulted in dose dependent antinociceptive behavior in the rat paw formalin test. S(+)-flurbiprofen was significantly more potent than the non-cyclooxygenase inhibiting R(-)-enantiomer with a potency ratio of about 3 to 1. Chiral inversion was very low and does not seem to account for the action of R(-)-flurbiprofen. In a modified Randall Selitto assay also both enantiomers were active in a dose dependent manner following systemic administration. Following local administration into the inflamed paw only S(+)-flurbiprofen showed significant dose related antinociceptive effects. R(-)-flurbiprofen was unable to block prostaglandin E2 induced hyperalgesia following local administration. Consequently, a central site of action independent of prostaglandin synthesis inhibition has to be discussed with respect to antinociceptive activity following systemic administration.