Topical ocular hypotensive activity and ocular penetration of dichlorphenamide sodium in rabbits

A single topical instillation (50 microliter) of the water soluble sodium salt of dichlorphenamide (10%) produced a pronounced and prolonged lowering of intraocular pressure (IOP), compared to suspensions of its free acid, in rabbits with alpha-chymotrypsin-induced ocular hypertension. In normal rabbits, instillation of dichlorphenamide sodium also produced a markedly elevated drug aqueous humor level relative to instillation of its free acid, indicating enhanced penetration into the eye. The IOP response after ocular instillation of dichlorphenamide sodium was equivalent to that produced by oral administration of 6 or 18 mg/kg dichlorphenamide sodium. Serum drug levels were lower and aqueous humor and iris-ciliary body levels were higher after instillation of dichlorphenamide sodium (10%) than after oral administration of 2 or 6 mg/kg. The data indicate that topically instilled dichlorphenamide sodium is capable of lowering IOP by a local action in the eye and provides a rationale for the potential utility of topical carbonic anhydrase inhibitors as a therapy for glaucoma in man.