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  • 1
    Electronic Resource
    Electronic Resource
    Can oral contraceptive steroids influence the elimination of nifedipine and its primary pryidine metabolite in humans? (1998)
    Springer
    European journal of clinical pharmacology 54 (1998), S. 729-734 
    Details
    ISSN: 1432-1041
    Keywords: Key words Oral contraceptives ; Nifedipine ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract Objective: To investigate the influence of oral contraceptives on cytochrome P450 3A4 (P450NF) activity. Methods: In 23 healthy women, the pharmacokinetics of nifedipine and its main metabolite dehydronifedipine in plasma were assessed after a single oral dose, prior to and after intake of one of two oral contraceptive formulations, one containing 2 mg dienogest and 0.03 mg ethinylestradiol (group A) and the other containing 0.125 mg levonorgestrel and 0.03 mg ethinylestradiol (group B). Results: While the intake of two oral contraceptives for 21 days did not influence the plasma concentration-time curve of unchanged nifedipine, mean AUC0–23.5 h and the mean Cmax values of dehydronifedipine were significantly lower in both groups tested/(24% in group A and 25% in group B). This observation may indicate a reduced formation rate of metabolites and reflects an inhibition of cytochrome P450 3A4 activity. The activation of the same or other metabolic degradation mechanism(s) could explain this result. Conclusion: The investigation presented demonstrates the importance of metabolite measurement when in vivo studies are undertaken to investigate different influences on drug metabolizing ability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002280050543
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Grapefruit juice inhibits 7-hydroxylation of coumarin in healthy volunteers (1994)
    Springer
    European journal of clinical pharmacology 46 (1994), S. 175-177 
    Details
    ISSN: 1432-1041
    Keywords: Grapefruit juice ; Coumarin ; Flavonoids ; Pharmacokinetics ; cytochrome P450 ; metabolism inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The effect of grapefruit juice on the urinary excretion of 7-hydroxycoumarin after oral administration of 10 mg coumarin, as an index of cytochrome P450 dependent coumarin metabolism, has been investigated in an open, randomised cross over study in 13 healthy volunteers (7 female, 6 male). The percentage of 7-hydroxycoumarin found in urine was significantly decreased up to 8 h after simultaneous intake of 300 ml grapefruit juice. If the same volume of juice was swallowed 30 min prior to the administration of coumarin, 7-hydroxycoumarin excretion was delayed by up to 6 h. MRTexcr. of coumarin was 70 % extended by coadministration of grapefruit juice. It appears that grapefruit flavonoids inhibit cytochrome P450 2A dependent metabolic pathways. The mechanism of cytochrome P450 inhibition by these flavonoids is still poorly understood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199885
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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