Dorzolamide — NZ Medication Guide

What is Dorzolamide?

Dorzolamide (generic name: dorzolamide hydrochloride) is a medication used primarily for reducing intraocular pressure in glaucoma and ocular hypertension. Dorzolamide 2% eye drops (Trusopt) are available on prescription in New Zealand, funded by Pharmac for glaucoma management. The combination product dorzolamide/timolol (Cosopt) is also available and funded.

What is Dorzolamide Used For?

Dorzolamide is prescribed by healthcare professionals in New Zealand for the following indications:

• Open-angle glaucoma
• Ocular hypertension
• Adjunct to other glaucoma medications (especially beta-blocker eye drops)
• Pseudoexfoliative glaucoma

How Does Dorzolamide Work?

Dorzolamide is a topical carbonic anhydrase inhibitor. It inhibits carbonic anhydrase II in the ciliary processes of the eye, reducing the production of aqueous humour. This decreases intraocular pressure. Unlike oral carbonic anhydrase inhibitors (acetazolamide), dorzolamide is applied as eye drops with minimal systemic absorption, resulting in fewer systemic side effects while still effectively lowering eye pressure.

How to Take Dorzolamide

Apply one drop of dorzolamide 2% eye drops into the affected eye(s) two to three times daily as directed by your ophthalmologist. Wait at least 10 minutes between different eye drop medications if using multiple treatments. Remove soft contact lenses before instillation and wait 15 minutes before reinserting. Store at room temperature.

Common Side Effects

• Ocular burning, stinging, or discomfort on instillation
• Bitter taste in mouth immediately after administration
• Blurred vision (transient)
• Tearing or watery eyes
• Conjunctival redness
• Headache

Serious Side Effects — Seek Medical Attention

• Corneal oedema or decompensation in patients with pre-existing corneal endothelial disease
• Severe allergic reaction — widespread rash, angioedema
• Sulfonamide hypersensitivity (rare — dorzolamide is a sulfonamide derivative)
• Acute angle-closure glaucoma (if used incorrectly in susceptible patients)

Drug Interactions

• Oral carbonic anhydrase inhibitors (acetazolamide) — additive systemic effects; not recommended to combine
• High-dose aspirin — may increase dorzolamide toxicity in overdose (theoretical)
• Other glaucoma eye drops — commonly combined; follow ophthalmologist instructions for spacing doses

New Zealand Prescribing Information

In New Zealand, dorzolamide is often used as an adjunct to prostaglandin analogues or beta-blocker eye drops when monotherapy is insufficient. The combination Cosopt (dorzolamide 2% + timolol 0.5%) reduces the number of daily eye drop instillations, which improves patient adherence. Patients with sulfonamide allergy should discuss this with their ophthalmologist before starting dorzolamide, as it is a sulfonamide derivative.

Frequently Asked Questions

Why do I get a bitter taste after using dorzolamide eye drops?

This is a common and harmless effect caused by a small amount of the eye drops draining through the nasolacrimal duct into the back of the throat. This is normal and affects many patients with all types of eye drops. Using punctal occlusion (pressing the inner corner of your eye for 1–2 minutes after instillation) can reduce this effect.

Can I use dorzolamide with other eye drops?

Yes — dorzolamide is commonly used in combination with other glaucoma eye drops. Wait at least 10 minutes between different types of eye drops to ensure each is absorbed properly. If you use multiple eye drop medications, ask your pharmacist for guidance on the correct order and timing for instillation.

References & Further Information

The following New Zealand and international resources were used to inform this page:

• New Zealand Formulary — Dorzolamide
• Pharmac — Funded Medicines Schedule
• Glaucoma NZ — Treatment Options
• Medsafe — Trusopt Eye Drops Data Sheet

Reviewed by a Registered Pharmacist — KiwiMeds New Zealand