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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
    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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  • 3
    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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  • 4
    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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  • 5
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    Input rate-dependent stereoselective pharmacokinetics: Effect of pulsatile oral input (1994)
    Wiley
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0899-0042
    Electronic ISSN: 1520-636X
    Topics: Chemistry and Pharmacology
    Published by Wiley
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