Comparative effects of medetomidine enantiomers on in vitro and in vivo microsomal drug metabolism.
The effects of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, and its levo enantiomer (MPV-1441), on in vitro microsomal P450-dependent drug-metabolizing activities as well as on in vivo aminopyrine elimination and hexobarbital sleeping time were studied. Both enantiomers inhibited the oxidative metabolism of several model substrates and testosterone in rat liver microsomal incubations. Microsomal activities derived from control animals or rats pretreated with phenobarbital were more sensitive to inhibitory effects of dexmedetomidine than those from rats treated with 3-methylcholanthrene. Enzyme activities in human liver microsomes were also inhibited by dexmedetomidine. Retardation of the elimination of aminopyrine was dose-dependent; elimination was marginally retarded with doses up to 100 micrograms/kg (from 17 to 23 min.; both enantiomers). Higher doses of the levo enantiomer prolonged aminopyrine half-life to 78 (1 mg/kg) and 162 min. (10 mg/kg). The hexobarbital sleeping time was prolonged by the dose of 1 mg/kg of the levo enantiomer (128 min. versus 20 min. in controls), while the dose of 0.1 mg/kg had no effect (23 versus 20 min.). These studies indicate that both enantiomers of medetomidine are inhibitors of microsomal drug metabolism in vitro, but significant effects on aminopyrine elimination or hexobarbital sleeping time are apparent only at doses, which do not allow the use of dexmedetomidine because of excessive sedative effect.
Pelkonen
O
O
Department of Pharmacology and Toxicology, University of Oulu, Finland.
Puurunen
J
J
Arvela
P
P
Lammintausta
R
R
D000316:Adrenergic alpha-Agonists / Q000493:pharmacokinetics / Q000494:pharmacology*; D000632:Aminopyrine / Q000378:metabolism; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006591:Hexobarbital / Q000494:pharmacology; D007093:Imidazoles / Q000493:pharmacokinetics / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism; D013379:Substrate Specificity
D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D000632:Aminopyrine; D003577:Cytochrome P-450 Enzyme System; D006591:Hexobarbital; D020926:Medetomidine