[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Carbonic anhydrase inhibitors](https://durgical.com/en/pharmacology/classes/carbonic-anhydrase-inhibitors/) › Acetazolamide

[Pharmacology](https://durgical.com/en/pharmacology/) · [Carbonic anhydrase inhibitors](https://durgical.com/en/pharmacology/classes/carbonic-anhydrase-inhibitors/)

# Acetazolamide

A carbonic anhydrase inhibitor that lowers eye pressure and causes a mild acidosis. Used in glaucoma and to prevent altitude sickness.

Updated 2026-11-01

- Class: [Carbonic anhydrase inhibitors](https://durgical.com/en/pharmacology/classes/carbonic-anhydrase-inhibitors/)
- Enzyme: Carbonic anhydrase II
- ATC code: S01EC01
- WHO Model List of Essential Medicines

✂**Carbonic anhydrase II**Acetazolamide

ⓘ The figure shows acetazolamide bound to the zinc in the active site of human carbonic anhydrase II.

**Target in 3D:** Carbonic anhydrase II. PDB structure 3HS4 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3HS4) · Drag to rotate · pinch to zoom

## Mechanism of action

Acetazolamide's sulfonamide group binds the zinc ion in the active site of carbonic anhydrase. In the proximal tubule bicarbonate can no longer be reclaimed, so bicarbonate, sodium, potassium and water leave in the urine, the urine turns alkaline and the blood becomes mildly acidic. In the eye it reduces the formation of aqueous humour.

- Acetazolamide binds the zinc of carbonic anhydrase
- The proximal tubule cannot reclaim bicarbonate
- Alkaline urine and mild metabolic acidosis
- In the eye: less aqueous humour, lower pressure

## Pharmacokinetics

**Absorption**
Absorbed by mouth; also given IV

**Distribution**
Concentrates in red blood cells, which are rich in carbonic anhydrase, and binds plasma proteins

**Elimination**
Excreted by the kidneys; it accumulates in kidney failure

## Indications

- Open-angle and secondary glaucoma, as an adjunct [Open-angle glaucoma →](https://durgical.com/en/conditions/open-angle-glaucoma/)
- Acute angle-closure glaucoma before surgery [Acute angle-closure glaucoma →](https://durgical.com/en/conditions/acute-angle-closure-glaucoma/)
- Prevention of acute mountain sickness during rapid ascent
- Some epilepsies, as an adjunct [Epilepsy and seizures →](https://durgical.com/en/conditions/epilepsy-and-seizures/)
- Oedema from heart failure or drugs, as an adjunct [Heart failure →](https://durgical.com/en/conditions/heart-failure/)

## Adverse effects

### Common

- Tingling in the hands, feet and face
- Altered taste
- Drowsiness and fatigue
- Loss of appetite, nausea
- Increased urination

### Serious (rare, important)

- Metabolic acidosis, severe in older adults with reduced kidney function
- Hypokalaemia and hyponatraemia
- Kidney stones
- Severe sulfonamide reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anaemia, liver necrosis

## Contraindications

- Hypersensitivity to acetazolamide or sulfonamides
- Low sodium or potassium
- Marked kidney or liver disease, including cirrhosis (risk of hepatic encephalopathy)
- Adrenal insufficiency
- Hyperchloraemic acidosis
- Long-term use in chronic angle-closure glaucoma

## Key interactions

**High-dose aspirin**
Severe acidosis, lethargy, coma and death have been reported

**Phenytoin**
Higher phenytoin levels and more osteomalacia

**Lithium**
More lithium excretion and lower lithium levels

**Amphetamines**
Alkaline urine reduces their excretion and prolongs their effect

## What is monitored

- Electrolytes, especially potassium
- Blood pH or bicarbonate
- Complete blood count
- Kidney function

## Nursing care

- Ask about sulfonamide allergy before the first dose.
- Check potassium and bicarbonate as ordered; report weakness or rapid breathing.
- Teach that tingling and altered taste are common, and to report rash, sore throat, fever or unusual bleeding.
- Teach to drink enough fluids to lower the risk of kidney stones.
- In altitude sickness, it does not replace descent if severe symptoms appear.

## Pregnancy and breastfeeding

Avoided where possible, especially early in pregnancy: it caused limb defects in animal studies.

## Memory aid

ACETAZOLAMIDE makes «ACID-ozolamide»: it throws bicarbonate into the urine and leaves the blood acidic.

## Test yourself

Think of the answer, then tap the question to see it.

## What acid-base change does acetazolamide cause?

A hyperchloraemic metabolic acidosis with alkaline urine, from loss of bicarbonate in the proximal tubule.

## Why is acetazolamide contraindicated in cirrhosis?

Alkaline urine reduces ammonia excretion; the extra ammonia can cause hepatic encephalopathy.

## Which interaction with aspirin is dangerous?

With high-dose aspirin, severe acidosis, lethargy, coma and death have been reported.

## Why does acetazolamide help prevent acute mountain sickness?

Its metabolic acidosis stimulates breathing, which offsets the respiratory alkalosis of altitude and improves oxygenation.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/acetazolamide/)

## Related drugs

- [Mannitol](https://durgical.com/en/pharmacology/mannitol/)

## Related conditions

- [Open-angle glaucoma](https://durgical.com/en/conditions/open-angle-glaucoma/)
- [Acute angle-closure glaucoma](https://durgical.com/en/conditions/acute-angle-closure-glaucoma/)
- [Epilepsy and seizures](https://durgical.com/en/conditions/epilepsy-and-seizures/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

[← Back to the class: Carbonic anhydrase inhibitors](https://durgical.com/en/pharmacology/classes/carbonic-anhydrase-inhibitors/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - ACETAZOLAMIDE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=240ab24b-3124-4805-80c2-36dd1945e3b3) (DailyMed (U.S. National Library of Medicine), 2026); [Acetazolamide: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682756.html) (MedlinePlus (U.S. National Library of Medicine), 2017); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=S01EC01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [RCSB PDB - 3HS4: Human carbonic anhydrase II complexed with acetazolamide](https://www.rcsb.org/structure/3HS4) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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