Pharmacokinetic profile of idazoxan in the beagle dog

The alpha 2-antagonist idazoxan (2- (2- (1,4-benzodioxanyl))-2-imidazoline) has been given intravenously and orally to five beagle dogs at 1, 3 and 10 mg kg-1 doses. Idazoxan plasma levels were determined by a HPLC method. After intravenous administration, a linear kinetic behaviour was obtained. Half-life and mean residence time values ranged 105.2-117.1 and 138.1-154.0 min, respectively. Total plasma clearance values and volume of distribution at steady state values ranged from 25.6-32.1 (mL kg-1) min-1 and 3.60-4.36 L kg-1, respectively. After oral administration, time to peak values averaged around 1 h. Dose normalized peak concentration values ranged 161-182 ng mL-1. Bioavailability values ranged 60-88%. Low idazoxan bioavailability has been described in other animal species and attributed to a first-pass effect.