A 70-year-old man with POAG on timolol eye drops reports increasing shortness of breath and wheezing. Timolol is a non-selective beta-blocker. Through which receptor-mediated mechanism does topical timolol primarily lower intraocular pressure?

• A Beta-2 receptor stimulation increasing uveoscleral outflow
• B Beta-1 receptor blockade reducing aqueous production in the ciliary body
• C Beta-2 receptor blockade reducing aqueous production in the ciliary body ✓
• D Alpha-2 receptor stimulation reducing aqueous production

Explanation

Timolol is a non-selective beta-adrenergic antagonist that lowers IOP primarily by blocking beta-2 receptors on the ciliary epithelium, thereby reducing aqueous humour production. Beta-2 receptors predominate in the ciliary body. The side effects (bronchospasm) result from systemic absorption causing beta-2 blockade in bronchial smooth muscle.

Reference: Katzung BG, Basic and Clinical Pharmacology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.