Timolol

Timolol is a nonselective beta-adrenergic blocker used topically for ocular pressure control. Veterinary applications commonly involve combination treatment with a carbonic anhydrase inhibitor. It also has a prophylactic role in selected fellow eyes of dogs with unilateral primary glaucoma. The magnitude of pressure reduction differs among species and disease states.

Group

Ophthalmic nonselective beta-blocker

Mechanism of Action

Timolol blocks beta-adrenergic receptors in the ciliary body and reduces receptor-mediated cyclic-AMP signaling involved in aqueous secretion. Decreased aqueous-humor production lowers the volume entering the anterior chamber and can reduce intraocular pressure. Its effect complements drugs that suppress aqueous production through other pathways. Mild pupil changes can also occur in veterinary species.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Glaucoma adjunct	Reference only	TOPICAL	Every 12 h	One drop of 0.5% ophthalmic solution per affected eye; not sufficient as sole treatment for a marked acute IOP crisis.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Glaucoma adjunct	Reference only	TOPICAL	Every 12 h	One drop of 0.5% ophthalmic solution per affected eye; not sufficient as sole treatment for a marked acute IOP crisis.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Glaucoma adjunct	Reference only	TOPICAL	Every 12 h	One drop of 0.5% ophthalmic solution per affected eye; not sufficient as sole treatment for a marked acute IOP crisis.

Indications

Adjunctive reduction of intraocular pressure in selected canine, feline or equine glaucoma, including combination treatment with dorzolamide.
Specialist prophylactic treatment of the fellow eye in selected dogs with unilateral primary glaucoma to delay clinical onset.

Contraindications

Use cautiously or avoid with bronchospastic disease, clinically important bradycardia, heart block or decompensated heart failure.

Interactions

Systemic beta-blockers and other negative chronotropes may increase bradycardia.
Combination dorzolamide adds another IOP-lowering mechanism.

Adverse effects

Local irritation and miosis; systemic bradycardia, hypotension or bronchoconstriction may occur.

Toxicity

Remove excess exposure and provide cardiovascular/respiratory support for significant systemic beta-blockade.

Preparations

Preparation	Form	Strength	Route
Timolol 0.5% ophthalmic solution Timolol base equivalent, commonly supplied as maleate; do not substitute maleate salt mass without an equivalence statement.	Other	5 mg / mL	TOPICAL

Monitoring and Administration

Check IOP response, pulse and respiratory status. Systemic absorption can matter even after ocular dosing.

The source reports 0.25% as minimally effective in animals compared with 0.5%; do not infer equal efficacy from the human experience.