home > drugs a-z list > elestat (epinastine hcl ophthalmic solution) drug center > elestat (epinastine hcl ophthalmic solution) drug - clinical pharmacology

Mechanism of Action

Epinastine is a topically active, direct H1-receptor antagonist and an inhibitor of the release of histamine from the mast cell. Epinastine is selective for the histamine H₁-receptor and has affinity for the histamine H2receptor. Epinastine also possesses affinity for the α1, α 2-, and 5-HT2–receptors.

Pharmacokinetics

Fourteen subjects, with allergic conjunctivitis, received one drop of ELESTAT® ophthalmic solution in each eye twice daily for 7 days. On day 7, average maximum epinastine plasma concentrations of 0.04±0.014 ng/ml were reached after about two hours indicating low systemic exposure. While these concentrations represented an increase over those seen following a single dose, the day 1 and day 7 Area Under the Curve (AUC) values were unchanged indicating that there is no increase in systemic absorption with multiple dosing. Epinastine is 64% bound to plasma proteins. The total systemic clearance is approximately 56 L/hr and the terminal plasma elimination half-life is about 12 hours. Epinastine is mainly excreted unchanged. About 55% of an intravenous dose is recovered unchanged in the urine with about 30% in feces. Less than 10% is metabolized. The renal elimination is mainly via active tubular secretion.

Clinical Studies

Epinastine HCl 0.05% has been shown to be significantly superior to vehicle for improving ocular itching in patients with allergic conjunctivitis in clinical studies using two different models: (1) conjunctival antigen challenge (CAC) where patients were dosed and then received antigen instilled into the inferior conjunctival fornix; and (2) environmental field studies where patients were dosed and evaluated during allergy season in their natural habitat. Results demonstrated a rapid onset of action for epinastine HCl 0.05% within 3 to 5 minutes after conjunctival antigen challenge. Duration of effect was shown to be 8 hours, making a twice daily regimen suitable. This dosing regimen was shown to be safe and effective for up to 8 weeks, without evidence of tachyphylaxis.

Last reviewed on RxList: 1/9/2012
This monograph has been modified to include the generic and brand name in many instances.