What Are Carbonic Anhydrase Inhibitors?
Carbonic anhydrase inhibitors are medications used by eye doctors to manage and treat glaucoma. Glaucoma is an eye disease that is usually caused by high pressure inside the eye. Having high eye pressure damages the optic nerve and leads to peripheral vision loss, known as “tunnel vision”.
Carbonic anhydrase inhibitors work by reducing the amount of fluid produced by the eye, which lowers eye pressure. The medication is usually prescribed as an eye drop that is used two to three times a day. People who are allergic to sulfa drugs should not use carbonic anhydrase inhibitors. The most common side effects of the medication are a bitter taste and tingling of the fingers. Examples of carbonic anhydrase inhibitors are dorzolamide, brinzolamide, and acetazolamide.
Key Takeaways
- Carbonic anhydrase inhibitors are a type of medication mainly used to treat glaucoma.
- Glaucoma is an eye disease that can be caused by high eye pressure. High eye pressure damages the optic nerve inside the eye and leads to peripheral vision loss.
- Carbonic anhydrase inhibitors decrease the amount of fluid produced by the eye. This reduces eye pressure and prevents glaucoma damage.
Understanding Carbonic Anhydrase Inhibitors
Carbonic anhydrase inhibitors are a group of medications that are used to treat glaucoma. They work by decreasing the amount of aqueous fluid produced by the eye. Aqueous fluid is the clear fluid that fills the space in the eye between the cornea and the lens. The fluid carries many important nutrients and oxygen to the eye’s structures. The amount of aqueous fluid in the eye determines the intraocular pressure or eye pressure. Having too much aqueous fluid causes high eye pressure, which is dangerous to the eye’s health. Carbonic anhydrase inhibitors reduce eye pressure to a healthy amount.
This medication is most commonly prescribed as an eye drop but is also available as a swallowable pill. Brinzolamide and dorzolamide are eye drops. Acetazolamide is an oral tablet. Acetazolamide is rarely prescribed to anyone unless a serious vision-threatening type of glaucoma is diagnosed, known as acute angle closure glaucoma.
Mechanism Of Action
Carbonic anhydrase inhibitors reduce the amount of fluid produced by the eye. Aqueous fluid is made by an eye structure called the ciliary body. When the ciliary body makes too much fluid, the eye pressure becomes high. Carbonic anhydrase inhibitors decrease the enzyme that makes bicarbonate, a salt used to form the aqueous fluid. When a carbonic anhydrase inhibitor is used, there is less fluid produced by the ciliary body so the eye pressure becomes lower. This medication is beneficial for people with glaucoma. Glaucoma is usually caused by high eye pressure. A carbonic anhydrase inhibitor medication reduces eye pressure and prevents future glaucoma damage. Although carbonic anhydrase inhibitor medication can be used alone, they are frequently prescribed along with other glaucoma medications such as timolol or latanoprost.
How Do They Work?
Carbonic Anhydrase Inhibitors lower intraocular pressure by lowering the formation of aqueous fluid. The front part of the eye, between the lens and the cornea, is filled with a clear fluid called aqueous humor. It provides nutrients and oxygen to the structures inside the eye. Carbonic Anhydrase Inhibitors decrease aqueous fluid by stopping bicarbonate production.
There are many different types of glaucoma medications. All types of glaucoma medications aim to reduce eye pressure. Glaucoma medications reduce eye pressure in two main ways. Firstly, they can decrease the amount of fluid produced by the eye. Otherwise, they can increase the amount of fluid leaving the eye (outflow). Examples of different glaucoma medications include:
- Carbonic Anhydrase Inhibitors: decrease aqueous fluid production
- Examples: dorzolamide, brinzolamide, acetazolamide
- Beta Blockers: decrease aqueous fluid production
- Example: timolol
- Prostaglandin Analogs: increase aqueous fluid outflow
- Example: latanoprost
- Alpha Agonists: increase aqueous fluid outflow
- Example: brimonidine
Side Effects
Carbonic anhydrase inhibitor medication use has been linked to various side effects. The side effects may be more noticeable if you take the oral pill form of medication because the medication is more likely to be absorbed into the bloodstream.
When carbonic anhydrase inhibitors are used as an eye drop, such as brinzolamide or dorzolamide, the following side effects may occur:
- Stinging sensation when the drop is put into the eye
- Metallic or bitter taste in the mouth
- Nausea
- Eye irritation
- Red eyes
- Temporarily blurry vision
When carbonic anhydrase inhibitors are used as an oral pill that is swallowed, such as acetazolamide, the following side effects may occur:
- Tingling in hands and feet
- Metallic taste
- More nearsighted eyeglasses prescription shift
- Weight loss
The most serious side effects of carbonic anhydrase inhibitors are aplastic anemia and metabolic acidosis. Aplastic anemia occurs when your body stops producing enough new blood cells. Metabolic acidosis happens when too much acid builds up in the body. These side effects are very rare, especially when taking the eye drop form of medication.
Types Of Carbonic Anhydrase Inhibitors
Acetazolamide
Acetazolamide is an oral tablet medication. It decreases the amount of fluid throughout the body and in the eye. Its brand name is Diamox. Acetazolamide is used to treat acute angle closure glaucoma, in which the eye pressure rises extremely high because it cannot be drained out of the eye. Acetazolamide is also used to decrease high intracranial pressure inside of the brain, for conditions like papilledema or idiopathic intracranial hypertension.
Dorzolamide And Brinzolamide
Dorzolamide and brinzolamide come in the form of an eye drop. The brand name for dorzolamide is Trusopt and the brand name for brinzolamide is Azopt. When used alone, they should be used three times a day. If they are prescribed along with another glaucoma medication such as latanoprost, they are typically used twice a day. The eye drop may need to be put into one eye or both.
Necessary Precautions
Pharmacists can provide patients with advice on dosage, administration, and possible side effects. It is important to take medication as prescribed by your eye doctor. Missing doses will decrease the effectiveness of treatment. Frequently forgetting to take your medication can increase the risk of glaucoma progressing, or getting worse over time.
Carbonic anhydrase inhibitors should be avoided if you have:
- Pregnancy
- Sulfa allergy
- Chronic obstructive pulmonary disease (COPD)
- Liver disease
- Kidney disease
