Pharmacology · Thiazide and thiazide-like diuretics
Chlortalidone !
A long-acting thiazide-like diuretic for high blood pressure and oedema. Its effect lasts more than a day.
Updated 2026-11-01
Also called: Chlorthalidone
The figure shows one of chlortalidone's two mirror-image forms (the S form) bound to the human NCC; the medicine is a mixture of both.
Mechanism of action
Chlortalidone is a sulfonamide that is not a true thiazide in structure but acts in the same way: it blocks the Na⁺-Cl⁻ cotransporter (NCC) of the distal convoluted tubule. More sodium and chloride are lost in the urine, potassium is lost in the collecting duct, and calcium reabsorption rises. Its long duration gives steady control of blood pressure.
- Chlortalidone blocks NCC in the distal tubule
- Na⁺ and Cl⁻ are lost in the urine; K⁺ follows downstream
- Calcium reabsorption rises
- Long action: steady lowering of blood pressure
Pharmacokinetics
- Absorption
- Absorbed by mouth
- Elimination
- Mostly excreted unchanged by the kidneys
- Onset and duration
- Diuresis begins in about 2.6 hours and lasts up to 72 hours
Indications
- High blood pressure Arterial hypertension →
- Oedema from heart failure, cirrhosis, corticosteroids or kidney disease Heart failure →
Adverse effects
Common
- Hypokalaemia and hyponatraemia
- High uric acid and gout
- Higher blood glucose
- Dizziness on standing
- Photosensitivity and rash
- Impotence
Contraindications
- Anuria
- Hypersensitivity to chlortalidone or other sulfonamide-derived drugs
Key interactions
- Lithium
- Less lithium clearance and risk of toxicity
- Digoxin
- Hypokalaemia increases digoxin toxicity
- Corticosteroids
- More potassium loss
- Insulin or oral antidiabetics
- Blood glucose may rise, changing their needs
What is monitored
- Potassium, sodium and calcium
- Kidney function
- Blood pressure
- Glucose and uric acid
Nursing care
- Before giving: blood pressure and potassium; report low values.
- Watch for signs of low potassium or sodium: weakness, cramps, confusion.
- In diabetes, check blood glucose more often at the start.
- Teach: take it in the morning, rise slowly, protect the skin from the sun, report muscle cramps or joint pain (gout).
Pregnancy and breastfeeding
Not used for ordinary oedema in pregnancy; it crosses the placenta, with a risk of jaundice or low platelets in the newborn.
Test yourself
Think of the answer, then tap the question to see it.
How does chlortalidone differ from hydrochlorothiazide?
It is a thiazide-like sulfonamide with a different ring structure and a much longer duration of action, but it blocks the same NCC transporter.
Which mineral does chlortalidone tend to raise in the blood?
Calcium, because it increases calcium reabsorption in the distal tubule; marked hypercalcaemia can reveal hidden hyperparathyroidism.
Can you name two contraindications of chlortalidone?
Anuria and hypersensitivity to chlortalidone or other sulfonamide-derived drugs.
Related drugs
Related conditions
← Back to the class: Thiazide and thiazide-like diuretics
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 - CHLORTHALIDONE tablet (DailyMed (U.S. National Library of Medicine), 2026); Chlorthalidone: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 8VPP: Phosphorylated human NCC in complex with chlorthalidone (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.