Dynamics and kinetics of ophthalmic timolol

Timolol is a beta adrenergic antagonist in 0.25% or 0.5% eyedrop solution for glaucoma. In a double-blind crossover study in healthy males we measured systemic beta blockade, intraocular pressure, and timolol kinetics after the first and ninth 12-hourly dose of a 0.5% ophthalmic solution. Timolol ophthalmic and placebo were each given as 2 drops to each eye with precautions to prevent the normal loss of drug in tears and overflow (high dose) and as 1 drop to each eye with no special precautions (standard therapeutic dose). Exercise tachycardia, measured at 70 and 255 min after administration of drug, was lower at both levels. Postexercise 1-sec forced expiratory volume (FEV1) was not affected. Intraocular pressure measured at 3 and 8 hr after drug was lower at both dose levels. Timolol was consistently present in urine but was not detectable in most plasma samples. Dynamic effects were not greater after the ninth than after the first dose, and the urinary excretion data provided no evidence of drug cumulation.