title: Pharmacokinetic analysis of absorption and metabolism of dopamine and a dopamine prodrug in dogs.
abstract: Pharmacokinetic compartment models were constructed to describe the absorption and metabolism of dopamine (DA) and DA prodrug, N-(N-acetyl-L-methionyl)0,0-bis-eth-oxycarbonyl) dopamine(1). Plasma concentrations of DA, DA-SO4, and DOPAC after oral administration of DA to dogs, were analysed using the pharmacokinetic model assuming the contribution of first-pass metabolism for the formation of DA-SO4 and DOPAC. Though plasma concentration of DA was quite different from that of DA-SO4 or DOPAC, these data were simultaneously analysed with a good fitting curve. The apparent absorption rate constant of DA(K1) was proved to be much smaller than the apparent formation rate constants of DA-SO4(K2) or DOPAC(K3). It was found that the compartment model is useful for the evaluation of absorption and metabolic inactivation of DA. Plasma concentration of DA, N-(N-acetyl-L-methionyl)dopamine(2), DA-SO4, and DOPAC after oral administration of 1 were simultaneously analysed using the compartment model including the first-pass metabolism and two-fraction dissolution process. Good fitting curves were obtained. The apparent formation rate constant of 2(K4) is larger than that of DA-SO4(K5) or DOPAC(K6); thus it was shown that two protective groups of 1 reduced the metabolism of DA and 2 specially played an important role to the reduction of first-pass metabolism. From these results, it was found to be possible to give a pharmacokinetic interpretation for the mechanism of reduction of first-pass metabolism of DA.
authors.affiliation: Products Formulation Research Laboratory, Tanabe Seiyaku Co., Ltd., Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Murata
authors.forename: K
authors.initials: K
authors.lastname: Noda
authors.forename: K
authors.initials: K
authors.lastname: Kohno
authors.forename: M
authors.initials: M
authors.lastname: Samejima
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000097:blood; D000042:Absorption; D000818:Animals; D004285:Dogs; D004298:Dopamine / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D011355:Prodrugs / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D011355:Prodrugs; D015102:3,4-Dihydroxyphenylacetic Acid; C007558:dopamine 3-O-sulfate; D004298:Dopamine