Dorzolamide
Dorzolamide is a topical carbonic anhydrase inhibitor used to lower intraocular pressure. Its veterinary role includes primary and selected secondary glaucomas in dogs and cats, with additional equine applications. It is available alone or with timolol. Its pressure-lowering effect principally reflects reduced aqueous-humor formation rather than alteration of pupil size.
Group
Topical carbonic anhydrase inhibitor
Mechanism of Action
Dorzolamide inhibits carbonic anhydrase in the ciliary epithelium. Reduced bicarbonate formation alters linked ion transport and decreases movement of fluid into the posterior chamber. Lower aqueous-humor production reduces fluid inflow and helps lower intraocular pressure. A timolol partner supplies an additional aqueous-suppressing mechanism through beta-receptor blockade.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Glaucoma | Reference only | TOPICAL | Every 8–12 h | One drop of 2% ophthalmic solution into the affected eye; interval adjusted to measured IOP. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Glaucoma | Reference only | TOPICAL | Every 8–12 h | One drop of 2% ophthalmic solution into the affected eye; interval adjusted to measured IOP. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Glaucoma | Reference only | TOPICAL | Every 12 h | One drop of 2% ophthalmic solution into the affected eye; reassess IOP. |
Indications
- Reduction of intraocular pressure in dogs or cats with primary glaucoma or selected secondary glaucoma.
- Treatment of selected ocular hypertension in veterinary patients.
- Adjunctive pressure control in selected equine glaucoma.
- Specialist prophylactic management of the fellow eye in dogs with unilateral primary glaucoma to delay clinical disease, with disease-specific evidence.
Contraindications
- Hypersensitivity to the formulation; assess painful red eyes for the underlying cause.
Interactions
- Combination with timolol adds beta-blocker risks; systemic carbonic anhydrase inhibitors can add metabolic effects.
Adverse effects
- Stinging, conjunctival irritation, punctate keratitis or local hypersensitivity.
Toxicity
Excess ocular application mainly causes irritation; assess systemic effects after substantial ingestion.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Dorzolamide 2% ophthalmic solution 20 mg/mL dorzolamide equivalent, supplied as hydrochloride; ophthalmic use only. | Other | 20 mg / mL | TOPICAL |
| Dorzolamide/timolol 2%/0.5% ophthalmic solution Combination includes timolol; not a single-active preparation and no component-based calculation selected. | Other | dorzolamide 20 mg / mL + timolol 5 mg / mL | TOPICAL |
Monitoring and Administration
Measure IOP before and after treatment and examine the cornea and anterior chamber.
Avoid touching the bottle tip to the eye. Use pressure and disease response to choose twice- versus three-times-daily treatment.