Which beta blocker is cardio-selective?

• A. Timolol
• B. Levobunolol
• C. Betaxolol
• D. Latanoprost

Answer: (C)

The concept tested is beta-receptor selectivity in glaucoma medications. In the eye, beta-blockers reduce aqueous humor production by blocking beta-adrenergic receptors on the ciliary body. Blocking beta-1 receptors (cardio-selectivity) tends to have fewer bronchial side effects than blocking beta-2 receptors, which is why cardio-selective agents are preferred in patients with reactive airway disease.

Betaxolol is cardio-selective, meaning it predominantly blocks beta-1 receptors, providing the desired lowering of intraocular pressure with a reduced risk of bronchospasm compared with nonselective beta-blockers. Timolol and levobunolol are nonselective and block both beta-1 and beta-2 receptors, increasing the potential for systemic and respiratory side effects. Latanoprost is not a beta-blocker at all; it’s a prostaglandin analog that lowers intraocular pressure by a different mechanism (increasing outflow).