Comparison of a noncardioselective beta-adrenoceptor blocker and a cardioselective blocker in reducing aqueous flow in humans

G. R. Gaul, N. J. Will and R. F. Brubaker
Mayo Foundation, Rochester, MN 55905.

In a double-masked crossover study, the dose-response relationship for aqueous flow was determined for four concentrations of betaxolol hydrochloride and levobunolol hydrochloride in 19 normal subjects. One eye of each subject received every concentration of both drugs. Each concentration was administered once daily for 1 week. The fellow eye received a placebo. Aqueous flow was measured for several hours on the last day of administration of each concentration beginning immediately after drug administration. For levobunolol, the mean decrease in aqueous flow compared with baseline was 8% after 1 week's treatment with 0.017% levobunolol, 15% after treatment with 0.05%, 20% after treatment with 0.167%, and 32% after treatment with 0.5%. For betaxolol, the mean decrease in aqueous flow compared with baseline was 3% after 1 week's treatment with 0.017% betaxolol, 12% after treatment with 0.05%, 18% after treatment with 0.167%, and 17% after treatment with 0.5%. Levobunolol-treated eyes but not betaxolol-treated eyes showed a significant drug effect 1 week after discontinuing the drug therapy. The relative potency of the noncardioselective drug was greater than that of the beta 1-cardioselective drug, but the difference in potency was much less than would be expected solely based on their relative affinity for beta 2-receptors in other species and tissues.