A 62-year-old man using topical timolol eye drops for chronic open-angle glaucoma develops wheezing and breathlessness. His physician should recognise that this adverse effect occurs because:

• A Timolol directly irritates bronchial mucosa through the nasopharyngeal route
• B Timolol drains through the nasolacrimal duct and is systemically absorbed, blocking bronchial beta-2 receptors ✓
• C Timolol raises intraocular pressure, triggering a vagal bronchoconstrictor reflex
• D Timolol is converted to a sulfite metabolite that provokes bronchospasm

Explanation

Topical ophthalmic drugs reach the systemic circulation via conjunctival vessels and the nasolacrimal drainage pathway, bypassing first pass metabolism. Timolol is a non-selective beta blocker, so absorbed drug blocks bronchial beta-2 receptors and precipitates bronchospasm in susceptible patients. Punctal occlusion after instillation reduces systemic absorption. Betaxolol, a beta-1 selective agent, is the safer alternative in such patients.

Reference: KD Tripathi Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.