Topical timolol, at conventional, unilateral doses causes bilateral ocular beta-blockade in rabbits

The studies described herein reveal that unilateral 0.3% and 1% doses of timolol produce marked beta-adrenoceptor blockade in treated and in contralateral eyes which did not receive timolol. This indicates that unilateral, conventional topical doses of timolol administered to rabbits cause bilateral ocular beta-adrenoceptor blockade. In addition, 0.1% and 1% doses of timolol applied to one eye resulted in blockade of cardiovascular beta-adrenoceptors. Thus, the most likely explanation for bilateral ocular beta-blockade would be systemic absorption of timolol from the treated eye and redistribution to the fellow eye. Since contralateral eyes would not provide an adequate control in circumstances where a large dose of timolol is administered unilaterally, caution must be exercised in interpreting data obtained in laboratory animals with doses of timolol similar to those employed clinically. A 0.01% dose of timolol appears adequate to achieve marked, unilateral ocular beta-adrenoceptor blockade in rabbits.