Carbonic Anhydrase Inhibitors for Glaucoma
Master carbonic anhydrase inhibitors: mechanism, IOP reduction, systemic adverse effects and high-yield acetazolamide board traps.
Carbonic anhydrase inhibitors lower intraocular pressure mainly by:
Carbonic Anhydrase Inhibitors in 30 Seconds
Carbonic anhydrase inhibitors reduce aqueous humor production and lower IOP by inhibiting carbonic anhydrase in the ciliary body epithelium. Dorzolamide and brinzolamide are topical agents, while acetazolamide is the key oral agent. They are primarily adjuncts in glaucoma therapy.
Mechanism and IOP Lowering
Carbonic anhydrase catalyzes bicarbonate formation in the nonpigmented ciliary epithelium. Inhibiting this enzyme reduces sodium and fluid transport into the posterior chamber, decreasing aqueous humor production. Topical agents lower IOP about 15 to 20%. Oral acetazolamide is more potent but systemic adverse effects limit chronic use. Both routes share the same mechanism but differ in potency, adverse effects and practical duration of use.
Topical vs Oral Agents
- Dorzolamide (Trusopt): topical, twice or three times daily, sulfonamide derivative; available in a fixed combination with timolol (Cosopt). Exam relevance: Cosopt is the classic fixed combination.
- Brinzolamide (Azopt): topical suspension, twice or three times daily, similar efficacy to dorzolamide with better local tolerability. Exam relevance: suspension formulation distinguishes it from dorzolamide solution.
- Acetazolamide (Diamox): most potent oral CAI, used for acute angle closure and short-term pressure control. Exam relevance: know its systemic toxicity profile.
- Methazolamide: oral CAI with fewer systemic effects than acetazolamide. Exam relevance: alternative when acetazolamide is poorly tolerated.
Systemic Side Effects of Oral CAIs
- Metabolic acidosis: carbonic anhydrase inhibition causes bicarbonate loss in the urine, producing a non-anion gap metabolic acidosis with compensatory hyperventilation. Exam relevance: explains the sickling risk in sickle cell disease.
- Electrolyte changes: hypokalemia and hyponatremia may occur. Exam relevance: monitor patients on systemic therapy.
- Paresthesias: tingling of the hands and feet is very common, often the first symptom patients report. Exam relevance: the classic acetazolamide adverse effect on boards.
- Renal stones: risk increases with dehydration, particularly calcium phosphate stones from alkaline urine. Exam relevance: ask about nephrolithiasis history before prescribing.
- GI symptoms: nausea, anorexia and malaise commonly limit adherence. Exam relevance: major reason patients discontinue oral therapy.
- Sulfonamide allergy: cross-reactivity is debated but use with caution in documented sulfonamide allergy. Exam relevance: recognize this prescribing concern.
- Aplastic anemia: extremely rare but potentially fatal. Exam relevance: a serious systemic adverse effect worth knowing.
- Renal failure: avoid in severe renal failure because systemic CAIs rely on renal excretion and can worsen metabolic acidosis. Exam relevance: check renal function before oral therapy.
- Topical CAI caution: use topical CAIs cautiously in corneal endothelial dysfunction because they may worsen corneal edema. Exam relevance: a favorite OKAP pharmacology distinction.
4 Facts Exams Always Ask
- Topical CAIs (dorzolamide and brinzolamide) lower IOP 15 to 20% by inhibiting carbonic anhydrase in the nonpigmented ciliary epithelium.
- Acetazolamide is the oral CAI of choice for acute angle closure and short-term use when maximum pressure control is needed.
- Paresthesias (tingling in the extremities) are the classic and most common systemic adverse effect of oral acetazolamide.
- Avoid acetazolamide in sickle cell disease because systemic acidosis promotes erythrocyte sickling, and use with extreme caution in severe renal failure.
The Classic Trap
Topical CAIs cause a bitter taste when medication drains through the nasolacrimal duct into the throat. This is a local administration effect, not systemic toxicity. Oral acetazolamide is avoided in sickle cell disease because metabolic acidosis promotes sickling, a highly tested board point. Do not confuse the bitter taste of topical CAIs with the systemic paresthesias of oral acetazolamide.
Clinical Pearl
Acetazolamide rapidly lowers IOP in acute angle closure before laser peripheral iridotomy and is a key step in the standard treatment sequence. The classic board adverse effect question is paresthesias. Always ask about sulfonamide allergy, sickle cell disease and renal function before prescribing. Topical CAIs are systemically well tolerated and add IOP lowering when combined with prostaglandins or beta-blockers.
Checkpoint 1
A common complaint after using dorzolamide eye drops is:
Checkpoint 2
Which medication is a systemic carbonic anhydrase inhibitor?
A patient with acute angle closure receives oral acetazolamide before laser treatment. Shortly afterward they report tingling in both hands. Which drug mechanism explains both the rapid IOP reduction and this classic systemic adverse effect?
Which sulfa-related adverse effect is a key contraindication consideration before prescribing oral acetazolamide for acute angle closure?
Sources & Publisher Info
Last clinically reviewed: August 9, 2026
References
- American Academy of Ophthalmology. Basic and Clinical Science Course, Section 10: Glaucoma.
- American Academy of Ophthalmology. EyeWiki: Glaucoma Medical Therapy.
- American Academy of Ophthalmology. EyeWiki: Topical Glaucoma Medications.
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