A carbonic anhydrase inhibitor eye drop
Dorzolamide
A carbonic anhydrase inhibitor eye drop used to lower raised pressure in the eye in glaucoma; it can cause stinging and a bitter taste.
What is Dorzolamide?
Dorzolamide is an eye drop used to lower raised pressure inside the eye in glaucoma and ocular hypertension. It works by reducing how much fluid the eye produces. It commonly causes stinging when first put in and a bitter taste, and people with a sulfonamide (sulfa) allergy need to use it with caution.
Education and reference only. This is a plain-language guide to Dorzolamide — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Dorzolamide is a carbonic anhydrase inhibitor eye drop used in the UK to lower raised pressure inside the eye in glaucoma and ocular hypertension, where high pressure can slowly damage the optic nerve and threaten sight. It may be used on its own or together with other glaucoma drops when one medicine is not enough, and it is also available combined with a beta-blocker drop in one bottle. It does not restore sight that has been lost; it protects vision by keeping eye pressure down, so it is usually used long term.
How it works
The pressure inside the eye depends on the balance between the fluid (aqueous humour) the eye makes and the fluid that drains away. Dorzolamide blocks an enzyme called carbonic anhydrase in the eye, which is involved in producing this fluid. By slowing fluid production it reduces the amount of aqueous humour, which lowers the pressure inside the eye and helps protect the optic nerve over time.
Company & origin
Originated / developed by: Developed by Merck & Co..
Dorzolamide is a carbonic anhydrase inhibitor eye drop developed by Merck and introduced in the 1990s to lower pressure in the eye.
What it treats
Conditions Dorzolamide is used for
Practical use
How to take Dorzolamide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Wash your hands, tilt your head back and put the drop into the pocket made by gently pulling down the lower lid.
- Close your eye and press gently on the inner corner near your nose for a short while; this reduces absorption and can lessen the bitter taste.
- Leave a gap of several minutes between dorzolamide and any other eye drops so each has time to work.
- If you wear contact lenses, follow your team's advice about removing them before the drop and waiting before putting them back.
- Tell your prescriber if you have ever had a serious reaction to sulfonamide ('sulfa') medicines.
- Use the drops regularly as prescribed, even though you may not feel any difference, to keep protecting your sight.
Weighing it up
Advantages & disadvantages of Dorzolamide
Advantages
- It effectively lowers eye pressure to help protect sight in glaucoma.
- It can be used alone or combined with other glaucoma drops, including in a single combined bottle.
- It has little effect on the heart or breathing, which can suit people who cannot use beta-blocker drops.
Disadvantages
- Stinging or burning when the drop goes in is common.
- A bitter or unusual taste afterwards is frequent and can be unpleasant.
- It is related to sulfonamide medicines, so people with a sulfa allergy need caution.
Practical use
Good to know
Stinging or burning when you put the drop in, blurred vision for a moment, and a bitter or unusual taste afterwards are common; the taste happens because a little drains down into the throat. Dorzolamide is related to sulfonamide ('sulfa') medicines, so if you have had a serious allergic reaction to sulfa drugs you should tell your prescriber and use it with caution. Pressing gently on the inner corner of the eye after the drop reduces how much is absorbed and can lessen the taste. If you wear contact lenses, ask your team about removing them before the drop and when to put them back in. Use the drops regularly even though you may not feel any difference, as the benefit is in protecting your sight.
Who should not take it / use with caution
- People who have had a serious allergic reaction to dorzolamide or to sulfonamide ('sulfa') medicines.
- People with significantly reduced kidney function (your team will advise).
- Anyone advised against it by their eye specialist for their particular eye condition.
Monitoring
- Regular checks of eye pressure to confirm the drops are working.
- Reviews of the optic nerve and visual fields to protect sight over time.
- Watching for eye irritation or an allergic-type reaction with longer use.
Side effects
- Stinging or burning in the eye when the drop is used.
- A bitter or unusual taste in the mouth afterwards.
- Blurred vision briefly after the drop and watery or red eyes.
- A gritty or irritated feeling, or an allergic-type eye reaction with longer use.
Key interactions
- Other carbonic anhydrase inhibitors (such as acetazolamide tablets) are not usually combined, as effects can add up.
- High-dose aspirin and some other medicines may interact, so tell your prescriber about all your medicines.
- Leave a gap between dorzolamide and other eye drops so they do not wash each other out.
Available as: Eye drops, including a form combined with a beta-blocker in one bottle.
Answers
Dorzolamide: frequently asked questions
How do dorzolamide drops lower eye pressure?
They block an enzyme in the eye that helps produce the fluid (aqueous humour) that fills it. By slowing fluid production, less builds up, so the pressure inside the eye falls, which helps protect the optic nerve in glaucoma.
Why do I get a bitter taste after using the drop?
A little of the drop drains from the eye down the tear duct into the back of the nose and throat, where you taste it. Pressing gently on the inner corner of the eye after the drop reduces this drainage and can lessen the taste.
I'm allergic to sulfa antibiotics — can I use dorzolamide?
Dorzolamide is chemically related to sulfonamide ('sulfa') medicines, so a serious sulfa allergy is an important reason for caution. Tell your prescriber about your allergy so they can decide whether it is safe for you.
Does the stinging mean something is wrong?
A short period of stinging or burning when the drop goes in is common and usually settles quickly. If you get severe pain, marked redness, swelling or a rash, stop and seek advice, as this could be an allergic reaction.
Why keep using the drops if I feel no different?
Glaucoma usually causes no symptoms until sight is already affected. The drops work silently by keeping eye pressure down to protect your vision, so it is important to keep using them regularly even when you feel no change.
The wider class
About Glaucoma eye drops
Dorzolamide belongs to the glaucoma eye drops class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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