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  • 1
    Electronic Resource
    Electronic Resource
    Enantioselective Kinetics of Verapamil and Norverapamil in Isolated Perfused Rat Livers (1994)
    Springer
    Pharmaceutical research 11 (1994), S. 1815-1819 
    Details
    ISSN: 1573-904X
    Keywords: verapamil ; noverapamil ; stereoselective metabolism ; isolated perfused rat liver ; metabolite kinetics, first-pass metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the individual enantiomers of verapamil (VER) and its metabolite, norverapamil (NOR), were studied in isolated perfused rat livers (IPRLs) after administration of racemic drug or the preformed metabolite. After constant infusion of 20 µg/min of racemic VER to single-pass IPRLs, the hepatic availabilities (F) of the enantiomers were low (S-VER, 0.069 ± 0.030; R-VER: 0.046 ± 0.025) and stereoselective (S:R ratio, 1.6 ± 0.2). After administration of similar doses, the F values of the preformed NOR enantiomers (S-NOR: 0.24 ± 0.04; R-NOR, 0.10 ± 0.02) were higher than those of the VER enantiomers. However, the stereoselectivity in F of NOR (S:R ratio, 2.2 ± 0.1), was in the same direction of that of VER. Further, the fractions of R enantiomers unbound to bovine serum albumin in the perfusate were higher than those of their antipodes for both VER (R:S ratio, 1.9 ± 0.1) and NOR (R:S ratio, 2.6 ± 0.2). Therefore, for unbound moieties, modest stereoselectivity in the metabolism of VER in favor of the S-isomer and no stereoselectivity in the metabolism of NOR were observed. Overall, our data suggest that the stereoselective protein binding is a primary determinant of stereoselectivity in the hepatic availability of VER and NOR in IPRLs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018935921473
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  • 2
    Electronic Resource
    Electronic Resource
    Pharmacokinetic Analysis of the Enantiomeric Inversion of Chiral Nonsteroidal Antiinflammatory Drugs (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 76-79 
    Details
    ISSN: 1573-904X
    Keywords: chiral drugs ; enantiomeric inversion ; first-pass metabolism ; nonsteroidal antiinflammatory drugs ; ibuprofen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Equations describing plasma concentration–time courses of the individual enantiomers of chiral 2-arylpropionic acid nonsteroidal antiinflammatory drugs were derived from a general model. The model assumes first-order absorption and elimination of the enantiomers with presystemic and/or systemic R-to-S enantiomeric inversion. Utilizing reported pharmacokinetic parameters, plasma concentrations of the enantiomers of ibuprofen (IB) were simulated. In the case of presystemic inversion, S:R plasma concentration ratios remained constant after an initial rise; the ratio progressively increased with time, however, when systemic inversion was assumed. Under the assumption of simultaneous systemic and presystemic inversion, the increase in the ratio in the postabsorptive phase was preceded by a steeper increase during absorption. Furthermore, it was shown that purturbation of IB absorption from the gastrointestinal tract may serve as an important discriminative measure for identification of the inversion site. For systemic and presystemic inversions, negative and positive sigmoidal relationships, respectively, were observed between the S:R concentration ratio 5 hr after drug administration and the time to reach the maximum plasma concentration. The applicability of the model to previously reported IB data is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015979915771
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  • 3
    Electronic Resource
    Electronic Resource
    Dextran-Methylprednisolone Succinate as a Prodrug of Methylprednisolone: Immunosuppressive Effects After In Vivo Administration to Rats (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1402-1407 
    Details
    ISSN: 1573-904X
    Keywords: methylprednisolone ; dextran-methylprednisolone conjugate ; immunosuppression ; lymphocyte proliferation ; splenocytes ; targeted delivery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To study the immunosuppressive activities of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednis- olone succinate (DEX-MPS), in rats. Methods. Single 5 mg/kg (MP equivalent) doses of MP or DEX-MPS were administered intravenously to rats, and blood and spleen samples were collected over 96 h. The immunosuppressive activity was determined by the effects of the free or dextran-conjugated drug on the mitogen-stimulated spleen lymphocyte proliferation. Additionally, the number of lymphocytes in the spleen cell suspensions was estimated. Further, the plasma and spleen concentrations of the conjugated and free MP were determined using size-exclusion and reversed-phase chromatographic methods, respectively. Results. Both MP and DEX-MPS injections resulted in the inhibition of the spleen lymphocyte proliferation. However, the maximal effect of DEX-MPS was significantly (P 〈 0.003) more intense (∼100% inhibition) and delayed (24 h) relative to that of MP (∼50% inhibition at 2 h). The DEX-MPS injection also resulted in a significantly (P 〈 0.0001) higher decline in the estimated number of spleen lymphocytes (∼80% at 24 h), compared with the MP injection (∼30% at 2hr). Whereas the plasma and spleen concentrations of MP could not be measured at ≥2 h after the drug injection, relatively high concentrations of DEX-MPS persisted in plasma and spleen for 24 h and 96 h, respectively. Conclusion. Dextran-methylprednisolone conjugate can effectively deliver the corticosteroid to its site of action for immunosuppression, resulting in more intense and sustained effects when compared with the free drug administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007555107691
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  • 4
    Electronic Resource
    Electronic Resource
    Liquid Chromatographic Analysis of the Enantiomeric Impurities in Various (+)-Pseudoephedrine Samples (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 1430-1433 
    Details
    ISSN: 1573-904X
    Keywords: high-performance liquid chromatography ; enantiomeric purity ; optical purity ; enantiomeric separation ; ephedrine ; pseudoephedrine ; precolumn derivatization ; S( + )-1-(1-naphthyl)-ethyl isocyanate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An HPLC method has been developed for the separation of four stereoisomers of ephedrine using precolumn derivatization with S( + )-l-(l-naphthyl)-ethyl isocyanate. The formed derivatives are subsequently separated on a normal-phase column and are detected at a UV wavelength of 220 nm. This method was used to quantitate the differences in the enantiomeric impurity of various samples of ( + )-pseudoephedrine. The reported method can differentiate between samples of ( + )-pseudoephedrine which differ in their enantiomeric impurity by as little as 0.02%. Possible racemization of ( + )-pseudoephedrine in aqueous solutions was also studied. Samples of ( + )-pseudoephedrine from various suppliers and, indeed, different lots from the same supplier, differed significantly in their degree of enantiomeric impurity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015813509816
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  • 5
    Electronic Resource
    Electronic Resource
    Stereospecific High-Performance Liquid Chromatographic (HPLC) Assay of Fenoprofen Enantiomers in Plasma and Urine (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 53-56 
    Details
    ISSN: 1573-904X
    Keywords: fenoprofen ; high-performance liquid chromatography (HPLC) ; nonsteroidal antiinflammatory drugs (NSAID) ; fenoprofen enantiomers ; diastereoisomer separation ; stereospecific analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new high-performance liquid chromatographic (HPLC) assay suitable for pharmacokinetic studies of enantiomers of fenoprofen (FEN) was developed. Following the addition of internal standard (IS; racemic ketoprofen), the plasma or urine constituents are extracted into a mixture of isooctane:isopropanol (95:5), back extracted into water, and finally, extracted into chloroform. After evaporation of the organic layer, the drug and IS are derivatized with l-leucinamide hydrochloride via ethyl chloroformate intermediate. The formed diastereoisomers are chromatographed on a reversed-phase HPLC with a mobile phase consisting of monopotassium phosphate solution:acetonitrile:triethylamine (65:35:0.02) at a flow rate of 1 ml/min. The detection UV wavelengths are 232 and 275 for the drug and IS, respectively. The suitability of the assay for pharmacokinetic analysis of FEN enantiomers was examined by analysis of the plasma and urine samples taken from a healthy subject, following peroral administration of a single 300-mg dose of racemic FEN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015867513045
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship of Apparent Systemic Clearance to Individual Organ Clearances: Effect of Pulmonary Clearance and Site of Drug Administration and Measurement (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 306-312 
    Details
    ISSN: 1573-904X
    Keywords: apparent systemic clearance ; organ clearance ; pulmonary clearance ; hepatic clearance ; arteriovenous concentration gradient ; first-pass metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relationships between apparent total-body clearance (CL) and individual organ clearances were mathematically defined with respect to the site of drug administration and measurement. The derived equations can be applied to drugs undergoing different pathways of elimination, including pulmonary clearance. A physiological pharmacokinetic model was used to test the validity of the equations. The apparent systemic clearance values obtained through the equations, using the individual organ clearance values, were identical to those calculated utilizing the model-generated data, indicating the validity of the equations. Furthermore, it was shown that the conventional estimation of CL of drugs subject to pulmonary clearance is highly dependent upon the site of drug administration and measurement. The relationships were further utilized to explain the reported CL values which are higher than the cardiac output. The equations developed here may be used to predict the contribution of different organs, such as the lungs, to the apparent systemic clearance of drugs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015881112716
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  • 7
    Electronic Resource
    Electronic Resource
    Input rate-dependent stereoselective pharmacokinetics: Effect of pulsatile oral input (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 185-195 
    Details
    ISSN: 0899-0042
    Keywords: stereoselective pharmacokinetics ; stereoselective bioavailability ; bioequivalence of chiral drugs ; nonlinear pharmacokinetics ; Michaelis-Menten kinetics ; computer simulation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Computer simulation was used to test the effects of pulsatile oral input on the stereoselectivity in the area under the blood concentration-time curves (AUCs) of the enantiomers of racemic drugs. The effects of input rate determinants, namely, dose, dosage interval, and formulation on the stereoselectivity were investigated under both steady-state and nonsteady-state conditions. Simulations were carried out for drugs undergoing Michaelis-Menten hepatic metabolism with different enantiomeric maximum velocity (Vmax) or constant (Km) values. With pulsatile input, the enantiomeric AUC ratios of both types of drugs were dependent on all the determinants of input rate. However, in most cases, the direction of input rate-dependent changes in the enantiomeric AUC ratios for drugs with different enantiomeric Vmax was opposite of that for drugs with different enantiomeric Km. The direction and magnitude of changes in the enantiomeric AUC ratios were also dependent on the selected dose, dosage interval, and formulation. Further, different conclusions could be reached based on the nonsteady-state and steady-state data. Additional simulations were then performed to test the effects of input rate-dependent stereoselective pharmacokinetics on the bioequivalence of chiral drugs with nonlinear metabolism. These simulations suggested that bioequivalence studies based on the racemic drug measurement may result in erroneous conclusions for the individual enantiomers. The results of this study may be used as a tool for the design of experiments to test the input rate dependence of stereoselective pharmacokinetics and bioequivalence of racemic drugs in animals and humans. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530060305
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  • 8
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    Delivery of NADPH-Cytochrome P450 Reductase Antisense Oligos Using Avidin−Biotin Approach (2010)
    American Chemical Society
    Details
    Publication Date: 2010-02-17
    Print ISSN: 1043-1802
    Electronic ISSN: 1520-4812
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society
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  • 9
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    Rapid determination of reduced and oxidized glutathione levels using a new thiol-masking reagent and the enzymatic recycling method: application to the rat liver and bile samples (2006)
    Springer
    Details
    Publication Date: 2006-03-18
    Print ISSN: 1618-2642
    Electronic ISSN: 1618-2650
    Topics: Chemistry and Pharmacology
    Published by Springer
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  • 10
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    Effects of Methylprednisolone and Its Liver-Targeted Dextran Prodrug on Ischemia–Reperfusion Injury in a Rat Liver Transplantation Model (2007)
    Springer
    Details
    Publication Date: 2007-10-06
    Print ISSN: 0724-8741
    Electronic ISSN: 1573-904X
    Topics: Chemistry and Pharmacology
    Published by Springer
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