Carbonic anhydrase inhibitor (diuretic)
Acetazolamide is a medicine that reduces fluid production in the eye (used in glaucoma), acts as a diuretic and is also used to prevent altitude (mountain) sickness. It works by inhibiting an enzyme called carbonic anhydrase. It can cause tingling in the hands and feet, taste changes, fatigue and, with prolonged use, a risk of kidney stones.
Also known as: Diamox
Adding acetazolamide to furosemide may deepen metabolic acidosis and hypokalaemia.
Acetazolamide (carbonic anhydrase inhibitor) promotes renal loss of bicarbonate, sodium, water and potassium, and furosemide also causes potassium loss and hypochloraemic alkalosis; the acetazolamide label contraindicates its use when serum sodium and/or potassium levels are depressed. Together, the risk of hypokalaemia, hyponatraemia and alkalosis is additive, with potential for arrhythmias, weakness and clinical worsening in patients with heart or liver failure. Monitor serum electrolytes (potassium, sodium, bicarbonate) and renal function during the combination.
Acetazolamide + furosemide: additive renal potassium loss with a risk of hypokalaemia and alkalosis. Monitor electrolytes.
Both cause bicarbonate/chloride and potassium loss; risk of marked metabolic acidosis.
Potassium, chloride, pH.
Signs of acidosis (Kussmaul breathing) or arrhythmia.
Monitor gases and electrolytes; use cautiously in the elderly.
DailyMed (FDA) — approved Acetazolamide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=268db224-d5db-457c-86bc-972c9fe07917 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Alcohol may increase central nervous system depression (drowsiness, dizziness) during acetazolamide treatment.
Limit alcohol intake during treatment.
DailyMed/FDA (NIH/NLM) — approved Acetazolamide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4813b9dd-5f58-44bb-ad64-cdb331828080
Taking acetazolamide with food reduces gastrointestinal discomfort (nausea, diarrhoea).
Take with food if gastric discomfort occurs.
DailyMed/FDA (NIH/NLM) — approved Acetazolamide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4813b9dd-5f58-44bb-ad64-cdb331828080
Acetazolamide is contraindicated in hepatic cirrhosis because it may precipitate hepatic encephalopathy.
Do not use in patients with hepatic cirrhosis.
EMC-UK (MHRA) — approved Acetazolamide SmPC: https://www.medicines.org.uk/emc/product/100949/smpc
Acetazolamide crosses the placenta; teratogenicity has been reported in animal studies, so it should be avoided in the 1st trimester.
Avoid in the 1st trimester; use only if the benefit outweighs the risk.
Acetazolamide is excreted into breast milk; avoid during breastfeeding because of a lack of data.
Use effective contraception during treatment in women of childbearing age.
EMC-UK (MHRA) — approved Acetazolamide SmPC: https://www.medicines.org.uk/emc/product/100949/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Carbonic anhydrase inhibitor with varied indications: glaucoma, epilepsy (absence seizures), oedema (heart failure, drug-induced) and prevention/relief of acute mountain sickness. A weak diuretic that alkalinises the urine and can cause metabolic acidosis.
Inhibits carbonic anhydrase (the enzyme catalysing CO2 hydration and carbonic acid dehydration). In the eye, it reduces aqueous humour secretion and intraocular pressure; in the kidney, it causes renal HCO3- loss with sodium, water and potassium elimination (urinary alkalinisation); in the CNS, it retards abnormal paroxysmal neuronal discharge.
Well absorbed orally; carbonic anhydrase inhibition in erythrocytes and tissues occurs within minutes of dosing. Used at 250 mg every 8-12 h (or 500 mg extended-release once daily) for acute mountain sickness prophylaxis.
Minimal metabolism; predominantly renal elimination unchanged (active tubular secretion). Urinary alkalinisation reduces tubular reabsorption of the drug.
Plasma half-life ~10-15 h; concentrates in erythrocytes (carbonic anhydrase binding), with an effect extending beyond the plasma half-life.
