Which medications in the drug class Carbonic anhydrase inhibitors are used in the treatment of Primary Open-Angle Glaucoma (POAG)?

Updated: Mar 16, 2020
  • Author: Kristin Schmid Biggerstaff, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Answer

Carbonic anhydrase inhibitors

Reduce secretion of aqueous humor by inhibiting carbonic anhydrase (CA) in the ciliary body. In acute angle-closure glaucoma, administer systemically; apply topically in patients with open-angle glaucoma. These drugs are less effective, and their duration of action is shorter than many other classes of drugs. Adverse effects are relatively rare but include superficial punctate keratitis, acidosis, paresthesias, anorexia, nausea, depression, dysgeusia, and lassitude.

Oral agents, such as acetazolamide and methazolamide, primarily are used only for the treatment of refractory POAG and secondary glaucomas because they have increased systemic adverse effects. However, oral CAIs can have a slightly greater effect than topical CAI medications and are appropriate to use in certain clinical situations. The mechanism of IOP reduction is similar to other CAIs, being accomplished by reduction of bicarbonate accumulation in the posterior chamber, with a resultant decrease in sodium and associated fluid movement linked to the bicarbonate ion. An additional IOP-lowering effect exists by the creation of a relative metabolic acidosis.

Dorzolamide (Trusopt)

More commonly used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer drugs at least 10 min apart. Either drug reversibly inhibits CA, reducing hydrogen ion secretion at renal tubule, and increases renal excretion of sodium, potassium bicarbonate, and water to decrease production of aqueous humor.

Brinzolamide (Azopt)

Catalyzes reversible reaction involving hydration of carbon dioxide and dehydration of carbonic acid. May use concomitantly with other topical ophthalmic drug products to lower IOP.

May cause less ocular discomfort on instillation, secondary to a buffered pH, but can still cause foreign body sensation.

If more than one topical ophthalmic drug being used, administer drugs at least 10 min apart.

Acetazolamide (Diamox)

Reduces rate of aqueous humor formation by direct inhibition of enzyme carbonic anhydrase (CA) on secretory ciliary epithelium, causing in turn a reduction in intraocular pressure (IOP). More than 90% of CA must be inhibited before IOP reduction can occur. May reduce IOP by 40-60%. Effects are seen in about an hour, they peak in 4 h, and trough in about 12 h. The usual maximum dose is 250 mg QID for tablets or 500 mg BID for long-lasting sequel capsules. It is derived chemically from sulfa drugs; however, cross-reaction allergy between sulfa-derived antibiotic and diuretic is not very common.

Used for adjunctive treatment of chronic simple (open-angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when delay of surgery desired to lower IOP

Methazolamide

Reduces aqueous humor formation by inhibiting enzyme carbonic anhydrase, which results in decreased IOP.


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