The pharmacokinetics and metabolism of idazoxan in the rat.
1. [2'-14C]Idazoxan was rapidly and completely absorbed after its oral administration to rats. 2. After administration of either [2'-14C] or [6,7-3H]idazoxan, radioactivity was taken up by a wide range of tissues and became localized, especially in the organs of metabolism and excretion. Quantitative distribution patterns were route-dependent such that oral dosing resulted in lower radioactivity concentrations in all tissues apart from liver. 3. Clearance of idazoxan (94-144 ml/min per kg) was due mostly to metabolism and was independent of dose. Oral bioavailability in male rats at low oral doses of idazoxan (10 mg/kg) was about 1%, but increased with increasing dose to 23% at 100 mg/kg. Oral bioavailability in female rats was considerably higher than in male rats, at all doses studied. Brain idazoxan levels were in equilibrium with those in plasma, but ten-fold higher. 4. Elimination of radioactivity after administration of 14C-idazoxan was via the urine and the faeces (about 75% and 20% of dose respectively) and occurred essentially in the 24 h period immediately after dosing. By 96 h after dosing, elimination was virtually complete, with less than 0.5% dose remaining in the carcasses. 5. Biotransformation was by hydroxylation at positions 6 and 7 to form phenolic metabolites, which were excreted as glucuronide and sulphate metabolites in urine, but unconjugated in faeces. Other minor metabolic routes were 5-hydroxylation or oxidative degradation of the imidazoline ring, but these pathways were of quantitatively minor importance in the rat.
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism / Q000493:pharmacokinetics*; D000818:Animals; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004146:Dioxanes / Q000378:metabolism / Q000493:pharmacokinetics*; D004147:Dioxins / Q000493:pharmacokinetics*; D004790:Enzyme Induction; D005260:Female; D006868:Hydrolysis; D019329:Idazoxan; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004147:Dioxins; D019329:Idazoxan