Effect of thymoxamine on the human pupil

The specificity of thymoxamine, an alpha-adrenoceptor antagonist was determined from in vitro organ bath studies using isolated preparations of canine saphenous and portal mesenteric veins. It was found that thymoxamine interacts mainly with postjunctional alpha-adrenoceptors. The miotic effects of topical thymoxamine hydrochloride were measured in normal human eyes using infrared pupillography. The effects of five different concentrations of thymoxamine were measured over time. Time-response and concentration-response relationships were calculated. The maximal pupillary response occurs at 60 min after instillation of the drug and has a half-life of 10 hr. The minimum effective concentration of thymoxamine is 0.01%, and the maximum effective concentration is 1.3%. Thymoxamine's properties could make it a clinically useful drug to diagnose angle-closure glaucoma, and also to reverse drug-induced mydriasis.