Dorzolamide
**Dorzolamide** is a topical carbonic anhydrase inhibitor used primarily for the management of **glaucoma** in dogs and cats. It is available as a single agent or in combination with the beta-blocker **timolol**. > **Clinical Pearl:** While the combination product is often more effective in dogs, cats typically achieve maximal intraocular pressure (IOP) reduction with dorzolamide alone. Note that its acidic pH (5.6) may cause more stinging upon application compared to brinzolamide.
Mechanism: Inhibits the enzyme **carbonic anhydrase** in the **ciliary body epithelium** → reduces the formation of **bicarbonate ions** → decreases fluid transport → reduces **aqueous humour production** → lowers **intraocular pressure (IOP)**.
Dosing by species
- Glaucoma · 1 drop/eye · topical · q8-12h · Maximal IOP lowering efficiency occurs with dorzolamide alone.
- Glaucoma · 1 drop/eye · topical · q8-12h · Dorzolamide/timolol combination may be more effective in dogs than either drug alone.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Severe hepatic impairment
- Severe renal impairment
- Uveitis (if using timolol combination)
- Anterior lens luxation (if using timolol combination)
Adverse effects
- Local irritation
- Blepharitis
- Keratitis
- Salivation
- Inappetance
- Bradycardia (with timolol combination)
- Hypotension (with timolol combination)
- Hypokalaemia (cats, rare)
- Metabolic acidosis (dogs, rare)
Monitoring
- Intraocular pressure (IOP)
- Signs of local irritation (blepharitis, keratitis)
- Serum potassium in cats (if used long-term)
- Acid-base status in dogs (if used long-term)
Overdose
No specific information provided in the monograph. Excessive topical application may increase the risk of systemic absorption, potentially leading to **metabolic acidosis** or **hypokalaemia**.
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.