Premium
ß 1 ‐ and ß 2 ‐antagonist activity of topically applied betaxolol and timolol in the systemic circulation
Author(s) -
Vuori MarjaLiisa,
AliMelkkilä Timo,
Kaila Timo,
Lisalo Esko,
Saari K. Matti
Publication year - 1993
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/j.1755-3768.1993.tb04661.x
Subject(s) - betaxolol , timolol , antagonist , pharmacology , beta (programming language) , receptor antagonist , medicine , chemistry , receptor , endocrinology , ophthalmology , glaucoma , computer science , programming language
Abstract. The ß 1 ‐ and ß 2 ‐antagonist activity of betaxolol and timolol in the systemic circulation was studied ex‐vivo after their ocular administration in thirty patients during cataract surgery. The patients received 40 μl of 0.5% betaxolol or 0.25% timolol into the lower cul‐de‐sacs of both eyes. Blood samples were collected up to four h after instillation of the doses. Plasma concentrations of betaxolol and timolol were analyzed using a radioreceptor assay. The ex‐vivo‐ß 1 ‐and ß 2 ‐receptor occupancies corresponding drug plasma levels were calculated using radioligand binding techniques. The extent of ß 1 ‐receptor occupancy of betaxolol in the systemic circulation was less than 20% and its ß 2 ‐receptor occupancy was negligible. The extent of ß 1 ‐receptor occupancy of timolol was about 65% and its ß 2 ‐receptor occupancy about 80%. Because receptor occupancy is the basis of antagonist activity of ß‐blocking agents, this study shows that the ß 1 ‐antagonist activity of betaxolol in the systemic circulation is much less than that of timolol, and that its ß 2 ‐antagonist activity is negligible. The study suggests that the reported side effects of betaxolol in patients with obstructive pulmonary diseases are not mediated via its ß 2 ‐receptor blocking properties.