The Ocular Pharmacokinetics of Ketanserin and Its Metabolite,Ketanserinol,in Albino Rabbits

ABSTRACT

Ketanserin, a hypotensive drug with 5-HT₂ receptor antagonism, when administered by topical infusion of a 0.25% w/v solution by corneal and scleral applications, was found to lower intraocular pressure with four times more activity than its metabolite, ketanserinol. Drug and metabolite were measured periodically in the corneal epithelium, corneal stroma/endothelium, aqueous humor, iris/ciliary body, conjunctiva, sciera and lens during the infusion period (0-120 min) and the postinfusion period (120-240 min) using a fluoro-metric reversed-phase HPLC assay developed and verified for the research. The infusion results showed that drag entered the eye by both the corneal and scleral routes. Lateral diffusion occurred between the conjunctiva and corneal epithelium. Drag and metabolite were also detected in the untreated fellow eyes, suggesting contralateral systemic redistribution. In vitro metabolism was studied and found to occur in the corneal epithelium, iris/ciliary body and bulbar and palpebral conjunctiva but not in the corneal stroma/endothelium, aqueous humor and sclera.

From noncompartmental analysis, zero-order infusion rate constants, first-order absorption constants, mean residence time, volumes of distribution at steady state (Vss) and clearance (Cle) were obtained using equations specific to the topical infusion method. Vss and Cle of aqueous humor (0.972 ml and 13.55 μl/min) were greater than aqueous humor volume (0.311 ml) and turnover rate (4.7 μl/min).