Carbonic Anhydrase Inhibitors for Glaucoma

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Carbonic Anhydrase Inhibitors for Glaucoma


Generic NameBrand Name
dorzolamide and timololCosopt

These medicines can be applied to the eye (topical), given in a pill form, or given through a needle into a vein (intravenous). Carbonic anhydrase inhibitors have orange bottle caps. If you need to use more than one type of eyedrop, you may need to take each medicine in a certain order. You can use the colour of the bottle cap to help you remember when to use each type of eyedrop.

If you are using more than one type of eyedrop, wait 5 minutes between eyedrop medicines.

How It Works

Carbonic anhydrase inhibitors decrease the pressure in the eyes by reducing how much fluid (aqueous humour) is produced in the eye.

Why It Is Used

Medicines taken by mouth (oral) are sometimes used when eyedrops for open-angle glaucoma have failed to keep the pressure down inside the eyes.

Carbonic anhydrase inhibitors are sometimes used in emergencies (in pill form or intravenously) to rapidly reduce the pressure inside the eye in closed-angle glaucoma.

How Well It Works

Carbonic anhydrase inhibitors can reduce the amount of fluid made in the eyes by 40% to 60%.1 Because the eye is making less fluid, this medicine can lower the pressure inside the eye.

If you have lower pressure inside your eye, your risk of damage to the optic nerve is lower, which can prevent further vision loss.

The pill form of these medicines is used for people whose glaucoma cannot be controlled by using eyedrops alone. These medicines have frequent side effects that affect the rest of the body.

Side Effects

Side effects of dorzolamide and brinzolamide include a stinging feeling in the eyes, blurred vision, inflammation of the clear covering of the eyes (cornea), and allergic reactions of the eyes. Dorzolamide and brinzolamide can occasionally cause total body side effects, but because they are given as eyedrops, these side effects are uncommon.

Side effects of carbonic anhydrase inhibitors that are taken by mouth or given through a vein include:

  • Bitter taste in the mouth.
  • Sluggishness.
  • Tingling in the hands and feet. (Many people who take the oral form of these medicines develop this side effect.)
  • Decreased appetite and weight loss.
  • Kidney stones.
  • Low potassium levels in the body.
  • Skin reaction.
  • Depression and decreased sex drive (less common).
  • Anemia (very rare).

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Carbonic anhydrase inhibitors (in pill form) can be used for long periods of time to treat people who have not been able to tolerate eyedrops. They are also used when eyedrops alone have not been effective in decreasing the pressure in the eyes.

These medicines are very effective at reducing the pressure in the eyes. For this reason, they are often used in emergency situations in which pressure inside the eyes needs to be decreased rapidly to prevent vision loss.

Some people who start taking these medicines have to stop taking them because of side effects. The pill or intravenous forms of these medicines are more likely to cause side effects than the eyedrop forms of other medicines.

Carbonic anhydrase inhibitors can make severe kidney disease, liver disease, or kidney stones worse. If you have had problems affecting the kidneys or liver, let your eye doctor know before you begin treatment with any of these medicines.

Complete the new medication information form (PDF) (What is a PDF document?) to help you understand this medication.



  1. Salmon JF (2008). Glaucoma. In P Riordan-Eva, JP Whitcher, eds., Vaughan and Asbury's General Ophthalmology, 17th ed., pp. 212–228. New York: McGraw-Hill.


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology
Last Revised August 2, 2010

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