Comparaison chez le volontaire sain du blocage bêta-adrénergique systémique par les collyres bêta-bloquants

Abstract

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 doubleblind 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 (f c), arterial systolic (Pa sys) and diastolic (Pa dia) 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 CD 25 (the amount of isoproterenol needed to increase f c 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 < 0.02). There was also a significantly greater fall in f c with both metipranolol and betaxolol than with placebo. There were no changes in Pa sys and Pa dia. CD 25 was significantly increased with both beta-blocker eye drops as compared with placebo (p < 0.05 for betaxolol ; p < 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). Although these results suggest a greater safety margin with both metipranolol and betaxolol, anaesthesiologists should be aware and wary of this phenomenon.