The Effect of H1-Blocking Antihistamines on Intraocular Pressure in Rabbits

Abstract

H1-blocking antihistamines were administered topically to rabbits to determine their effects on intraocular pressure. Chlorcyclizine which is in the piperazine class of H1-inhibitors was found to elevate intraocular pressure. This effect was prevented by the systemic administration of indomethacin and is probably a prostaglandin induced change. Of the other agents tested, antazoline which is in the ethylenediamine class, was the only drug found to lower intraocular pressure. The antazoline-induced lowering of intraocular pressure was associated with no changes in outflow facility, episcleral venous pressure, systemic blood pressure, or ocular blood flow. Tonographic and aqueous humor ascorbate data suggested a decreased (41% and 33% respectively) rate of aqueous flow as the mechanism for the decrease in intraocular pressure. The systemic administration of the alpha-adrenergic blocker phentolamine prevented the decrease in intraocular pressure but systemically administered blockers of cholinergic (atropine) or beta-adrenergic (propanolol) activity had no effect.