Carbonic Anhydrase Inhibitors (CAIs)
CAIs work by reducing the carbonic anhydrase
activity in the ciliary processes. In the ciliary epithelium,
the production of aqueous humor is a function of the production
of bicarbonate. By reducing bicarbonate production, aqueous
formation is reduced, thus decreasing IOP. These drugs can
be valuable in certain patients. However, with the availability
of the more clinically efficacious drugs such as beta-blockers
and prostaglandins, the CAIs have a relatively limited role
in reducing IOP.
Since these drugs inhibit bicarbonate function,
there is some concern that corneal endothelial function may
be partially compromised. Likewise, mucin production by corneal
epithelial cells is somewhat dependent on bicarbonate function.
These concerns are gaining more ground in the literature and
until research further elucidates the impact of CAIs on endothelial
and epithelial function, it would be wise to use these drugs
with caution in patients with clinically significant guttata,
endothelial compromise, those with significant ocular surface
disease, and especially in eyes that have sustained surgery.
Although CAIs are sulfa-based compounds, these topical drugs
probably do not share sulfa allergy with sulfonamide antibacterials
because of significantly different chemical structures. But
until widespread use proves this, it is best to avoid CAIs
in patients with a true sulfa allergy. Also, no measurable
amount of these drugs is found in blood plasma, so there is
little or no impact on renal physiology. See "A
Fresh Look At Sulfa Allergy" under the Literature Review section.
Carbonic anhydrase inhibitors are available in both ocular
and systemic forms, but the advent of topical therapy has reduced,
but not totally eliminated, the need for oral therapy.
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