Each week we will aim to bring out a concise email that provides 4-5 key pieces of information addressing a specific issue in clinical therapeutics.
This week: Systemic Adverse Effects of Beta-Blocker Containing Eye Drops
Csilla Burt, Clinical Pharmacist, Ward MM
Beta-blocker containing eye drops are commonly used for the treatment of glaucoma. Timolol is a non-selective beta-blocker which can cause systemic adverse effects due to the presence of beta adrenoreceptors in the vascular smooth muscle, the heart and the lungs. Risk of adverse effects especially if systemic absorption occurs, may be significant in the elderly and those with comorbidities.
- After topical administration, a significant amount of the drop is drained through the nasolacrimal duct and absorbed directly into the systemic circulation.
- First pass hepatic metabolism is bypassed meaning the effects of the drug resemble that of intravenous administration. It has been found that one drop of 0.5% timolol solution placed in each eye is approximately equivalent to 10 mg of an oral dose of timolol.
- Systemic side effects that can occur include bradycardia, bronchospasm, hypotension and syncope.
- Elderly patients with co-existing cardiovascular and respiratory diseases may be particularly vulnerable to adverse effects.
- The co-prescription of topical and systemic beta-blockers has been known to reduce heart rate.
- Risk of dizziness and falls is increased.
- The use of the “DOT” technique (Digital Occlusion of the Tear duct), by applying pressure with the index finger over the lacrimal sac for 1-2 minutes with the eyes closed can reduce systemic absorption by up to 70%.
- Use of this technique is essential to reduce the likelihood of significant absorption of the drug into the systemic circulation thereby reducing risk of adverse effects and drug interactions.
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