Beta-Blocker Intolerance in a Patient on Triple Therapy
A 71-year-old man with primary open-angle glaucoma attends for routine review. He has used latanoprost 0.005% at night, timolol 0.5% twice daily, and brimonidine 0.2% twice daily for three years. Today his intraocular pressure is 16 mmHg right and 17 mmHg left, with thin central corneas (498 and 502 µm) and a documented visual field defect in the right eye. He reports two months of exertional breathlessness and wheezing when climbing stairs and has been using a salbutamol inhaler that his general practitioner prescribed after a chest infection. His pulse is 52 beats per minute and regular, blood pressure 138/78 mmHg. An electrocardiogram shows first-degree heart block with a PR interval of 220 ms. He also mentions dry mouth and fatigue. He asks whether his eye drops could be responsible and is reluctant to stop any treatment because his father went blind from glaucoma.
1. Which of his topical medications is the most likely cause of the respiratory and cardiac findings, and what is the pharmacological reasoning?
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Timolol is the most likely culprit. Topical beta-blockers are absorbed systemically through the nasolacrimal mucosa and can block beta-2 receptors in the airways, causing bronchospasm and wheeze, and beta-1 receptors in the heart, causing bradycardia and AV conduction delay. His exertional breathlessness, salbutamol use, pulse of 52, and first-degree heart block with PR 220 ms fit this mechanism. A childhood history of asthma is a relative contraindication even when inactive. Brimonidine can cause fatigue and dry mouth, which he also reports, but it does not typically cause bronchospasm or heart block. Latanoprost is not associated with these effects. The timing, with symptoms developing over two months, is consistent with increased systemic exposure or a change in cardiac or airway status. He should be told that the drops may be contributing, but he should not stop all glaucoma treatment.
2. Propose a revised ocular hypotensive regimen, stating what you would stop, what you would substitute, and how you would monitor.
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Stop timolol, with the patient's consent, and do not substitute another beta-blocker. Continue latanoprost at night. For additional IOP lowering, consider a topical carbonic anhydrase inhibitor such as brinzolamide 1% or dorzolamide 2% twice daily, provided there is no sulfonamide allergy, or use a fixed combination that does not contain a beta-blocker. Brimonidine can be continued if it is tolerated, but its fatigue and dry mouth may limit adherence. Because he has thin corneas, a field defect, and a low target IOP, refer for selective laser trabeculoplasty and glaucoma specialist review rather than simply accepting an IOP in the high teens. Monitor IOP in 4-6 weeks, ask about breathlessness and pulse, and check adherence. The GP and cardiologist should assess the heart block and asthma; do not attribute all symptoms to the drops without medical review.
3. What non-pharmacological and communication steps are required, including referral and documentation?
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Document the discussion, the reason for stopping timolol, the new regimen, and the referrals. Advise punctal occlusion and eyelid closure after instillation to reduce systemic absorption. Tell him to seek urgent care for syncope, chest pain, or worsening breathlessness. Inform his glaucoma specialist and GP in writing. Review in 4-6 weeks with IOP, visual field, and adherence assessment; if IOP is above target, escalate to selective laser trabeculoplasty or specialist-managed options. Avoid changing all medications at once so that the effect of each change can be assessed.