Adverse Effects and Contraindications
Common adverse effects of topical CAIs include taste disturbance, blurred vision, burning upon instillation, and punctate keratopathy. Although many topical medications cause burning upon instillation, this is particularly common and more intense with dorzolamide, a solution formulated at a low pH due to the low solubility of the molecule at physiologic pH levels. Use of brinzolamide, a suspension, results in white deposits in the tear film. Eyes with compromised endothelial cell function may also be at risk of corneal decompensation with use of either of these drugs.
Adverse effects of systemic CAI therapy are usually dose related and are driven primarily by the resultant metabolic acidosis. Many patients experience paresthesias of the fingers or toes and report loss of energy and anorexia. Weight loss is common. Severe mental depression, abdominal discomfort, diarrhea, loss of libido, impotence, and taste disturbance, especially with carbonated beverages, may also occur. Patients with sickle cell anemia are at risk of sickle cell crisis. There is an increased risk of formation of calcium oxalate and calcium phosphate renal calculi. Because methazolamide causes less acidosis, it may be less likely than acetazolamide to cause nephrolithiasis.
As the urine becomes more alkaline, ammonia excretion is reduced. Systemic CAIs are contraindicated in patients with hepatic cirrhosis, because either systemic agent can precipitate hepatic encephalopathy due to increased serum ammonia levels.
CAIs are sulfonamides and thus are often thought to cause allergic reactions in individuals with known sulfonamide antibiotic allergies. Only about 10% of patients with hypersensitivity to sulfonamide antibiotics experience allergic reactions when exposed to sulfonamide nonantibiotics such as CAIs. Such a response is thought to represent a predisposition to allergic reactions rather than true cross-reactivity. It is prudent, however, to avoid prescribing CAIs to patients with a history of a severe allergic reaction to any sulfonamide. Aplastic anemia and other blood dyscrasias, Stevens-Johnson syndrome, and hepatic necrosis are very rare but potentially fatal idiosyncratic reactions to CAIs. Although routine complete blood counts have been suggested, they are not predictive of blood dyscrasias and are not routinely recommended. Hypokalemia is a potentially serious complication that is especially likely to occur when an oral CAI is used concurrently with another drug that causes potassium loss (eg, a thiazide diuretic). Serum potassium should be monitored regularly in such patients.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.