Comparison in healthy volunteers of the systemic beta adrenergic receptor blockade by beta blockader eye drops

The isoproterenol dose-response curve was used to assess quantitatively the degree of systemic beta-adrenoceptor blockade induced by metipranolol (Bétanol) and betaxolol (Bétoptic) eye drops. The study was carried out in twelve healthy volunteers, aged 22 +/- 1.4 yr. In a randomized double-blind trial, each volunteer received, on separate occasions at least one week apart, one drop in each eye of either placebo (physiological saline) or either of the ophthalmic beta-blockers. The intraocular pressure (Pio), heart rate (fc), arterial systolic (Pasys) and diastolic (Padia) pressures were measured before instillation of the eye drops after 15 to 30 min rest, and 3 h afterwards. The isoproterenol dose-response curve was studied 3 h after instillation of the drops. The CD25 (the amount of isoproterenol needed to increase fc by 25 b.min-1) was obtained by extrapolation on the least square linear regression curve. Both beta-blockers gave a significant fall in Pio compared with placebo, metipranolol more than betaxolol (p less than 0.02). There was also a significantly greater fall in fc with both metipranolol and betaxolol than with placebo. There were no changes in Pasys and Padia. CD25 was significantly increased with both beta-blocker eye drops as compared with placebo (p less than 0.05 for betaxolol; p less than 0.01 for metipranolol), but there was no difference between the two. Systemic absorption after topical application of ocular beta-blockers was thus confirmed for both metipranolol and betaxolol. However, the degree of beta-adrenoceptor blockade was weaker than that observed with other older ocular beta-blockers (timolol and carteolol).