Xyloglucan as a novel vehicle for timolol: Pharmacokinetics and pressure lowering activity in rabbits

This study was aimed at verifying the performances of a mucoadhesive polysa ccharide from tamarind seed (xyloglucan or TSP, tamarind seed polysaccharid e) as an adjuvant for ophthalmic vehicles containing timolol. Three formulations tone experimental vehicle based on TSP and two reference commercial eye drops) containing 5 mg/ml timolol base equivalents were adm inistered to the eyes of pigmented rabbits. Drug concentrations in tear flu id, cornea, iris-ciliary body, aqueous humor and plasma were determined, as well as intraocular pressure. The polymer under investigation, in spite of a comparatively low viscosity, produced high timolol concentrations in the ocular tissues and a low syste mic absorption. The performances of the TSP vehicle were comparable to thos e of a reference "in situ" gelling formulation (Timoptic(R) XE). The result s point to TSP as a potentially useful dadjuvant for ophthalmic delivery sy stems.