Ocular penetration of β-adrenergic blocking agents. An experimental study with atenolol, metoprolol, timolol and propranolol

Abstract

A comparison was made between the ocular penetration of topically applied ¹⁴C-atenolol, ¹⁴C-timolol, ¹⁴C-propranolol and ³H-metoprolol by means of liquid scintillation counting. Only one eye was treated, the fellow eye served as a control. Blood plasma levels were measured as well. We could detect a relationship between the ocular penetration and the degree of lipophilicity of the drugs used, as was to be expected. Drugs with a higher degree of lipophilicity penetrated more readily into the eye, whereas they also achieved higher blood plasma levels. Relatively high concentrations of atenolol were found in the nictitating membrane, thus reflecting its poor ocular penetration. The concentrations detected in the untreated eye were low and probably cannot explain the marked reduction in intraocular pressure observed after unilateral instillation of active β-adrenergic blocking drugs, as for instance timolol. Our findings suggest that the ocular penetration of β-adrenergic blocking agents on topical application only plays a minor part in their ocular hypotensive effect.