Azelastine

Absorption	Absorption of azelastine following ocular administration was relatively low. Systemic bioavailability is approximately 40% after nasal administration.
Volume of distribution	14.5 L/kg
Protein binding	In-vitro studies in human plasma indicate that the plasma protein binding of azelastine and N-desmethylazelastine are approximately 88% and 97%, respectively.
Metabolism	Azelastine hydrochloride is oxidatively metabolized to the principal metabolite, N-desmethylazelastine, by the cytochrome P450 enzyme system, however the exact cytochrome P450 isoenzyme involved has not been determined. The major metabolite, desmethylazelastine, also has H1-receptor antagonist activity. Enzyme Metabolite Reaction Km Vmax Cytochrome P450 2D6 Desmethylazelastine Cytochrome P450 1A2 Desmethylazelastine Cytochrome P450 3A4 Desmethylazelastine Cytochrome P450 2C19 Desmethylazelastine
Route of elimination	Approximately 75% of an oral dose of radiolabeled azelastine hydrochloride was excreted in the feces with less than 10% as unchanged azelastine. Azelastine hydrochloride is oxidatively metabolized to the principal metabolite, N-desmethylazelastine, by the cytochrome P450 enzyme system.
Half life	Elimination half-life (based on intravenous and oral administration) is 22 hours. Elimination half-life of the active metabolite, desmethylazelastine, is 54 hours (after oral administration of azelastine).
Clearance	0.5 L/h/kg [symptomatic patients]
Toxicity	Not Available