In order to find what types of hepatic microsomal cytochrome P450 (CYP) isozymes are involved in the metabolism of DA-8159 and in the formation of DA-8164 in rats, enzyme inducers, such as dexamethasone, phenobarbital, 3-methylcholanthrene and isoniazid, and enzyme inhibitors, such as troleandomycin and quinine, were pretreated in rats. After a 1 min intravenous administration of DA-8159 at a dose of 30 mg/kg to rats pretreated with dexamethasone (a main inducer of CYP3A1/2 in rats), the total areas under the plasma concentration-time curve from time zero to time infinity (AUC) values of DA-8159 (283 versus 349 microg min/ml) and DA-8164 (98.0 versus 79.8 microg min/ml) were significantly smaller and greater, respectively, than those in control rats. However, the AUC values of DA-8159 were not significantly different after pretreatment with phenobarbital, isoniazid and 3-methylcholanthrene (main inducers of CYP2B1/2, 2E1 and 1A1/2, respectively, in rats). In rats pretreated with troleandomycin (a main inhibitor of CYP3A1/2 in rats), the AUC values of DA-8159 (435 versus 370 microg min/ml) and DA-8164 (34.8 versus 76.5 microg min/ml) were significantly greater and smaller, respectively. However, in rats pretreated with quinine (a main inhibitor of CYP2D1 in rats), the AUC of DA-8159 was comparable to that in control rats. The above data indicate that DA-8159 was metabolized and DA-8164 was formed mainly via CYP3A1/2 in rats.

Time-averaged total body clearance (Cl) and apparent volume of distribution at steady state (V(SS)) of DA-8159 after intravenous administration to mice (30 mg/kg), rats (30 mg/kg), rabbits (30 mg/kg) and dogs (3 mg/kg) were analysed as a function of species body weight (W) using the allometric equation for interspecies scaling, and were used to predict those in humans. Significant linear relationships were obtained between log Cl (l/h) and log W (kg) (r = 0.992; p = 0.0079) and log V(SS) (l) and log W (kg) (r = 0.999; p < 0.0001). The corresponding allometric equations were Cl = 4.36 W(0.492) and V(SS) = 6.41 W(0.911). These allometric equations were extrapolated to predict the Cl and V(SS) for DA-8159 in humans based on the 70 kg body weights. In addition, concentrations in the plasma-time profile predicted using the four animal data fitted to a complex Dedrick plot of animal data. Our results indicated that the DA-8159 data obtained from four laboratory animals could be utilized to generate preliminary estimates of the pharmacokinetic parameters in humans. These parameters can serve as guidelines for better planning of clinical studies.