acetazolamide

carbonic anhydrase inhibitor· Brands: Diamox, Diamox SequelsIVPO

Mechanism of action

Acetazolamide inhibits carbonic anhydrase, an enzyme that catalyzes the reversible hydration of carbon dioxide to carbonic acid and its dissociation into bicarbonate and hydrogen ions. Inhibition reduces the formation of hydrogen ions and bicarbonate in the proximal renal tubule, leading to increased excretion of bicarbonate, sodium, potassium, and water. This produces a metabolic acidosis and alkaline urine, and impairs the urinary acidification mechanism. In the eye, carbonic anhydrase inhibition reduces the secretion of aqueous humour by the ciliary body, lowering intraocular pressure; similar effects on the choroid plexus reduce cerebrospinal fluid production.

Pharmacokinetics

It is widely distributed, including into the cerebrospinal fluid and aqueous humour, and extensively bound to plasma proteins (about 90%).

Indications & dosing

Glaucoma (open-angle, chronic simple, secondary)

Adjunctive therapy; start at lowest dose and titrate.

adult · PO: 250–500 mg BD or QDS · Adjunctive therapy; start at lowest dose and titrate.

Epilepsy (adjunctive therapy)

Initially 250 mg OD; increase as tolerated. May be used in partial and tonic-clonic seizures.

adult · PO: 250–500 mg OD or BD · Initially 250 mg OD; increase as tolerated. May be used in partial and tonic-clonic seizures.

Altitude sickness (prevention and treatment)off-label

Prevention: 125-250 mg BD, start 24-48 h before ascent. Treatment: 250 mg TDS.

adult · PO: 125–250 mg BD or TDS · Prevention: 125-250 mg BD, start 24-48 h before ascent. Treatment: 250 mg TDS.

Idiopathic intracranial hypertension (pseudotumour cerebri)off-label

Used to reduce CSF production; monitor electrolytes.

adult · PO: 250–500 mg BD · Used to reduce CSF production; monitor electrolytes.

Contraindications & precautions

Hypersensitivity to acetazolamide or sulfonamides · Cross-sensitivity with sulfonamide antibiotics; avoid if history of severe reaction.
Severe renal impairment · Renal failure leads to drug accumulation and worsening metabolic acidosis.
Hepatic cirrhosis or severe hepatic impairment · May precipitate hepatic encephalopathy.
Metabolic acidosis · Acetazolamide can worsen pre-existing acidosis.
Pregnancy · Use only if potential benefit outweighs risk, especially in first trimester.
Lactation · Excreted in breast milk; not recommended.
Monitor serum electrolytes and acid-base balance regularly, especially during long-term therapy.
Ensure adequate hydration to reduce the risk of renal calculi.
Use with caution in patients with respiratory acidosis or chronic obstructive pulmonary disease.
Caution in elderly patients as they are more susceptible to electrolyte imbalances.
Avoid abrupt discontinuation in patients with epilepsy; taper gradually.
Be aware of potential interaction with high-dose salicylates, which may increase toxicity risk.

Adverse effects

Paraesthesia (tingling in extremities)
Metabolic acidosisserious
Hypokalaemiaserious
Gastrointestinal disturbances (nausea, vomiting, diarrhoea)
Polyuria
Renal calculiserious
Stevens-Johnson syndromeserious
Aplastic anaemiaserious

Renal & hepatic adjustment

eGFR 30–60: Use with caution. Consider reducing dose or increasing dosing interval, especially if used for long-term therapy. Monitor electrolytes and renal function.
eGFR 15–30: Reduce dose (e.g., to 250 mg once daily or every other day) and monitor closely for metabolic acidosis.
eGFR 0–15: Contraindicated. Acetazolamide is not recommended in severe renal impairment. (avoid)
Hepatic impairment (mild): No dose adjustment required; use with caution.
Hepatic impairment (moderate): Use with caution; monitor acid-base status as metabolic acidosis may worsen hepatic encephalopathy.
Hepatic impairment (severe): Avoid use in severe hepatic impairment. (avoid)

Monitoring, pregnancy & toxicity

Serum electrolytes (sodium, potassium) · Baseline and periodically during treatment
Acid-base status (serum bicarbonate, blood pH) · Baseline and within 1-2 weeks of starting therapy; repeat if risk of acidosis
Renal function (serum creatinine, eGFR) · Baseline and periodically
Intraocular pressure · As clinically indicated if used for glaucoma
Full blood count · Periodically during long-term therapy
Pregnancy: Contraindicated in pregnancy (especially first trimester) due to teratogenic risk in animals. Use effective contraception in women of childbearing potential; consider alternative therapy.
Toxicity: Metabolic acidosis (with elevated anion gap) · Correct with sodium bicarbonate if severe; monitor acid-base status.
Toxicity: Electrolyte imbalances (hypokalemia, hyponatremia) · Replace electrolytes; consider potassium supplementation; monitor serum levels.
Toxicity: CNS effects (headache, confusion, ataxia, drowsiness) · Supportive care; consider dose reduction or discontinuation.
Toxicity: Sulfonamide hypersensitivity reactions (rash, fever, blood dyscrasias) · Discontinue immediately; provide antihistamines or corticosteroids if needed; monitor blood counts.

Clinical notes

Acetazolamide is used to treat glaucoma, acute mountain sickness, and metabolic alkalosis, and occasionally as an adjunct in epilepsy. It may also be used to manage symptomatic hydrocephalus and to alkalinise urine. The main side effects include paraesthesia, metabolic acidosis, hypokalaemia, and gastrointestinal disturbances; it may also cause myelosuppression and renal stones. Use with caution in patients with renal or hepatic impairment, or with a history of sulfonamide allergy, because of cross-reactivity. Monitor electrolytes, blood counts, and renal function during prolonged therapy. Doses are given for teaching: for glaucoma, the usual oral dose in adults is 250 mg twice daily to 1 g daily; for altitude sickness, 125 mg to 250 mg twice daily, starting 24 h before ascent. IV formulations may be used when oral therapy is not possible. Always follow local guidance.

Log in to read the full acetazolamide monograph

A free account unlocks the complete drug reference, the interaction checker, prescription practice and every other learning tool.

BNF; local formulary