1. Clinical Overview
Dorzolamide is a topical, potent, and reversible inhibitor of carbonic anhydrase II (CA-II), used primarily as an ophthalmic solution for the reduction of elevated intraocular pressure (IOP) in patients with ocular hypertension or open-angle glaucoma. It decreases aqueous humor production by the ciliary processes in the eye. In the Indian context, it is a first-line or adjunctive therapy, widely available and cost-effective.
| Onset | Duration | Bioavailability |
|---|---|---|
| Approximately 2 hours after topical ocular administration. | The IOP-lowering effect persists for at least 8 hours. For 24-hour control, twice-daily dosing is standard. | Systemic bioavailability after topical ocular administration is very low (<5%). The drug acts primarily locally. |
2. Mechanism of Action
Dorzolamide is a sulfonamide derivative that inhibits carbonic anhydrase isoenzyme II (CA-II), which is found in high concentration in the ciliary processes of the eye. Inhibition of CA-II reduces the formation of bicarbonate ions, leading to a reduction in sodium and fluid transport. This results in a decrease in aqueous humor secretion and a subsequent reduction in intraocular pressure (IOP).
3. Indications & Uses
- Elevated intraocular pressure (IOP) in patients with ocular hypertension
- Open-angle glaucoma (as monotherapy or adjunctive therapy)
4. Dosage & Administration
Adult Dosage: One drop in the affected eye(s) 3 times daily. Often used as twice daily (BID) in fixed-dose combinations (e.g., with Timolol).
Administration: 1. Wash hands. 2. Tilt head back. 3. Gently pull lower eyelid to form a pouch. 4. Instill one drop. 5. Close eye gently for 1-2 minutes, apply gentle pressure to the nasolacrimal duct (inner corner of eye) to minimize systemic absorption. 6. Do not touch dropper tip to any surface. 7. Wait at least 10 minutes before instilling any other ophthalmic product.
5. Side Effects
Common side effects may include:
- Transient burning/stinging sensation in the eye (up to 33%)
- Bitter/Unusual taste following nasolacrimal drainage (up to 25%)
- Superficial punctate keratitis
- Conjunctival hyperemia (redness)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Oral Carbonic Anhydrase Inhibitors (Acetazolamide, Methazolamide) | Additive systemic effects, increasing risk of metabolic acidosis and electrolyte disturbances. | Major |
| High-dose Salicylates (Aspirin) | May displace dorzolamide from erythrocyte binding sites, potentially increasing systemic levels and toxicity. Risk of acidosis. | Moderate |
| Other Topical Beta-blockers (Timolol, Betaxolol) - when used separately | Additive IOP-lowering effect. Fixed-dose combinations exist to improve compliance. | Moderate |
| Drugs causing Hypokalemia (Diuretics, Amphotericin B) | Additive risk of hypokalemia due to systemic bicarbonate loss. | Moderate |
7. Patient Counselling
- DO wash hands before use.
- DO apply gentle pressure on the inner corner of the eye (nasolacrimal duct) for 1-2 minutes after instillation to reduce systemic absorption and bitter taste.
- DO wait at least 10-15 minutes before inserting soft contact lenses (if worn).
- DO NOT touch the dropper tip to your eye, fingers, or any surface.
- DO NOT stop the medication without consulting your doctor, even if you feel fine.
- DO NOT use the solution if it changes color or becomes cloudy.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause acute life-threatening symptoms. Accidental ingestion may lead to symptoms of systemic carbonic anhydrase inhibition: electrolyte imbalance, metabolic acidosis (hyperchloremic), CNS effects (drowsiness, confusion), nausea, vomiting, dizziness, paresthesia.
Storage: Store at controlled room temperature (15°C to 25°C). Protect from light. Do not freeze. Keep the bottle tightly closed when not in use. Discard the bottle 4 weeks after first opening. Keep out of reach of children.