Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Overview
Dorzolamide is a topical carbonic anhydrase inhibitor used in veterinary ophthalmology to reduce intraocular pressure (IOP) in dogs and cats. It is commonly administered as ophthalmic drops either alone or in combination with timolol.
It is considered an effective option for long-term management of glaucoma and other conditions associated with increased IOP. The combination product (dorzolamide + timolol) may enhance IOP reduction in dogs, while dorzolamide alone is often sufficient in cats.
Mechanism of Action (MOA): Dorzolamide inhibits carbonic anhydrase in the ciliary body epithelium, reducing bicarbonate ion formation and consequently decreasing aqueous humor production, leading to reduced intraocular pressure.
Indications
Dorzolamide is used in dogs and cats for the management of increased intraocular pressure and glaucoma. It may be used as a single agent or as part of combination therapy depending on clinical response.
- Glaucoma management: Used in primary and secondary glaucoma to reduce intraocular pressure and prevent optic nerve damage.
- Adjunctive therapy: Commonly combined with other topical antiglaucoma medications when monotherapy is insufficient.
- Combination therapy (with timolol): May provide enhanced IOP reduction in dogs compared with either drug alone.
- Species-specific response: In cats, dorzolamide alone often achieves maximal IOP reduction without the need for combination therapy.
Dosage (Reference)
Dog
In dogs, dorzolamide is administered topically to control intraocular pressure. Frequency depends on severity of glaucoma and whether combination therapy is used.
| Clinical use | Route | Dose | Notes |
|---|---|---|---|
| Glaucoma / increased IOP | Ophthalmic | 1 drop/eye every 8–12 hours | May be used alone or with timolol; combination may improve efficacy. |
• Ensure proper administration technique to maximize ocular absorption.
• Combination with timolol may enhance IOP reduction.
• Monitor response and adjust frequency based on clinical effect.
Cat
In cats, dorzolamide is typically effective as a single agent for reducing intraocular pressure, with dosing similar to dogs.
| Clinical use | Route | Dose | Notes |
|---|---|---|---|
| Glaucoma / increased IOP | Ophthalmic | 1 drop/eye every 8–12 hours | Dorzolamide alone is usually sufficient for maximal IOP reduction. |
• Typically effective as monotherapy.
• Monitor for local irritation and tolerance.
• Adjust dosing interval based on clinical response.
Warnings & Precautions
Dorzolamide is generally well tolerated, but both local ocular effects and potential systemic absorption should be considered, particularly when used chronically or in combination with timolol.
- Hepatic and renal impairment: Contraindicated in severe hepatic or renal dysfunction due to altered drug metabolism and elimination.
- Timolol component: Causes miosis and may not be appropriate in conditions such as uveitis or anterior lens luxation.
- Systemic absorption: Although topical, systemic absorption may occur and contribute to adverse effects, especially with frequent dosing.
- Ocular tolerance: Dorzolamide may be less well tolerated than other agents due to its relatively acidic pH, increasing risk of local irritation.
Drug Interactions
No clinically significant drug interactions have been clearly documented for dorzolamide in dogs and cats.
- No established interactions: Current evidence does not indicate significant interactions, but caution is advised when combining with other topical ophthalmic drugs.
Side Effects & Overdose
Side Effects
Adverse effects are usually mild and localized but may occasionally include systemic effects, particularly with combination products or prolonged use.
- Local irritation: Ocular discomfort, conjunctival irritation, or stinging following administration.
- Blepharitis and keratitis: Inflammatory reactions affecting eyelids and cornea.
- Hypersalivation and inappetence: May occur due to systemic absorption or taste after nasolacrimal drainage.
- Bradycardia and hypotension: Associated with timolol-containing formulations.
- Electrolyte and metabolic effects: Rare cases of hypokalaemia in cats and metabolic acidosis in dogs have been reported.
Overdose
Overdose is uncommon with topical ophthalmic use but may increase the risk of both ocular and systemic adverse effects.
- Exaggerated local irritation: Increased ocular discomfort and inflammation.
- Systemic effects: Potential cardiovascular or metabolic disturbances, particularly with excessive dosing or combination therapy.
- Management: Discontinue the drug and provide supportive care as needed.
Key Notes
Practical clinical considerations for the use of dorzolamide in dogs and cats:
- First-line topical therapy: Commonly used for glaucoma management in both species.
- Species differences: Dogs may benefit more from combination therapy with timolol, whereas cats often respond well to dorzolamide alone.
- Administration frequency: Typically requires dosing every 8–12 hours for adequate IOP control.
- Local tolerance: May cause more irritation compared with other topical carbonic anhydrase inhibitors.
- Chronic use: Suitable for long-term management but requires monitoring of response and tolerance.
