Aging and the pharmacokinetics and metabolism of metoprolol enantiomers in the rat

After i.v. administration of racemic metoprolol in the rat, the plasma concentrations of (R)- and (S)-metoprolol were comparable, and no differences in pharmacokinetic parameters between the two enantiomers were found. From the 3rd to the 12th month, comparable changes were seen for both enantiomers...

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Bibliographic Details
Published in:Journal of gerontology (Kirkwood) 1993-05, Vol.48 (3), p.B108-B114
Main Authors: Vermeulen, A M, Belpaire, F M, De Smet, F, Vercruysse, I, Bogaert, M G
Format: Article
Language:English
Subjects:
Administration, Oral
Aging - metabolism
Animals
Cytochrome P-450 Enzyme System - metabolism
Half-Life
In Vitro Techniques
Injections, Intravenous
Liver - metabolism
Male
Metabolic Clearance Rate
Metoprolol - administration & dosage
Metoprolol - pharmacokinetics
Rats
Rats, Wistar
Stereoisomerism
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Summary:After i.v. administration of racemic metoprolol in the rat, the plasma concentrations of (R)- and (S)-metoprolol were comparable, and no differences in pharmacokinetic parameters between the two enantiomers were found. From the 3rd to the 12th month, comparable changes were seen for both enantiomers: there was an increase in the area under the plasma concentration-time curve (AUC) and a decrease in blood and plasma clearance. Half-life showed a significant prolongation, volume of distribution decreased between 3 and 12 months and increased between 12 and 24 months. After oral administration of the racemate, AUC and Cmax (maximum plasma concentration) were slightly higher, while oral clearance was slightly lower for (R)-metoprolol than for (S)-metoprolol. With aging, Cmax and AUC increased for both enantiomers, while oral clearance decreased. The change in oral clearance as a function of age is different between (S)- and (R)-metoprolol, and thus enantioselective. In vitro disappearance rate in 3-month-old rats was significantly higher for (S)-metoprolol than for (R)-metoprolol, although the difference was small. With aging, the disappearance rates of both enantiomers increased significantly, but not enantioselectively.
ISSN:0022-1422
2331-3323
DOI:10.1093/geronj/48.3.B108