Summary
The biotransformation of detomidine, a new a2-adrenoceptor agonist, was studied using rat as the model animal. In vivo metabolism of the tritiated drug was compared to in vitro incubations with liver homogenates and intact, isolated hepatocytes. Metabolites were analysed by HPLC with radioactivity detection.
The metabolic patterns in all systems were closely related. HPLC of urine gave twelve radioactive peaks. Tritiated water and unchanged3H-detomidine were minor components. The two major peaks were tentatively identified as hydroxylated detomidine (14%) and its O-glucuronide (43%). Sulphate conjugates were not found.
Isolated hepatocytes converted detomidine to the same two major products; the relative amount of the glucuronide increased with incubation time. In liver post-mitochondrial supernatant, hydroxylation was the dominant reaction, and the hydroxylated product comprised 74% of the total metabolites with non-induced and 50% with phenobarbital-induced liver.
The major biotransformation in rat was thus concluded to be hydroxylation by the liver monooxygenases followed by glucuronic acid conjugation. The maximal rate of oxidation or the enzymatic capacity of a whole liver was estimated to be at least 100 nmol/min allowing for a high hepatic extraction ratio for detomidine. Together with the effective excretion of the glucuronide, this reaction sequence alone could account for the rapid elimination of the drug.
Similar content being viewed by others
References
Virtanen R, Ruskoaho H, Nyman L. (1985): Pharmacological evidence for the involvement of or2-adrenoceptors in the sedative effect of detomidine, a novel sedativeanalgesic. J. Vet. Pharmacol. Ther. 8: 30–37.
Savola J-M, Ruskoaho H, Salonen JS, Puurunen J, Karki NT. (1987): Cardiovascular and sedative a2-adrenoceptor effects of detomidine-like arylalkylimidazoles and associated derivatives. Arzneimittelforsch, (in press).
Salonen JS. (1986): Pharmacokinetics of detomidine. Acta Vet. Scand. 2 (Suppl.82): 59–66.
Lowry OH, Rosenbrough NJ, Farr AL, Randall RJ. (1951): Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193: 265–275.
Seglen PO. (1976): Preparation of isolated rat liver cells. Methods Cell Biol. 13: 29–83.
Martin LE, Reid E. (1981): Isolation of drug metabolites. Prog. Drug Metab. 6: 197–248.
Vliegenthart JFG, Dorland L. (1970): Study by mass spectrometry of amino acid sequences in peptides containing histidine. Biochem. J. 117: 31P-32P.
Rypins EB, Sankary H, Wynn MJ. (1985): Bedside micromethod for measuring effective hepatic blood flow, with use of first-order galactose clearance pharmacokinetics. Clin. Chem. 31: 1557–1559.
Salonen JS, Virtanen R. (1983): Study of tissue distribution and elimination of radiolabeled detomidine in experimental animals. Acta Pharmacol. Toxicol. 53(Suppl.): 194.
Rendic S, Kajfez F, Ruf H-H. (1983): Characterization of Cimetidine, ranitidine, and related structures’ interaction with cytochrome P450. Drug Metab. Dispos. 11: 137–142.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Salonen, J.S., Suolinna, E.M. Metabolism of detomidine in the rat. I. Comparison of3H-labelled metabolites formed in vitro and in vivo. European Journal of Drug Metabolism and Pharmacokinetics 13, 53–58 (1988). https://doi.org/10.1007/BF03189929
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF03189929