Timolol
Timolol is a topical non-selective beta-blocker primarily used for the **management of canine and feline glaucoma**. It can be used as a monotherapy or in combination with other topical glaucoma drugs, such as carbonic anhydrase inhibitors (e.g., dorzolamide or brinzolamide). > **Clinical Warning:** Timolol causes miosis and may therefore not be the drug of choice in uveitis, anterior lens luxation, or pupil block. Systemic absorption can occur, leading to cardiovascular effects.
Mechanism: Timolol acts as a **non-selective beta-adrenergic receptor antagonist**. It decreases aqueous humour production via **beta-adrenoreceptor blockade** in the ciliary body, which subsequently lowers intraocular pressure (IOP).
Dosing by species
- Glaucoma · One drop per affected eye · topical · q8-12h · Can be used alone or in combination with dorzolamide/brinzolamide
- Glaucoma · One drop per affected eye · topical · q12h · Dorzolamide alone reaches maximal IOP lowering efficiency in cats
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Uncontrolled heart failure
- Asthma
- Uveitis
- Anterior lens luxation
- Pupil block
Adverse effects
- Miosis
- Conjunctival hyperaemia
- Local ocular irritation
- Bradycardia (systemic)
- Hypotension (systemic)
Drug interactions
- Oral beta-blockers · Additive adverse effects (bradycardia, hypotension) · major
- Calcium antagonists · Prolonged AV conduction times · major
- Digoxin · Prolonged AV conduction times · major
Monitoring
- Intraocular pressure (IOP)
- Heart rate and rhythm
- Blood pressure
Overdose
Overdosage via topical application is rare but may lead to exacerbated systemic effects such as **bradycardia**, **hypotension**, and **bronchospasm**. Treatment is supportive and symptomatic. Excess topical product should be flushed from the eye with sterile saline.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.