Pharmacology · Thiazide and thiazide-like diuretics
Chlorothiazide !
The first thiazide diuretic, available by mouth and as an IV injection. Used as an adjunct for oedema and in high blood pressure.
Updated 2026-11-01
Mechanism of action
Chlorothiazide blocks the Na⁺-Cl⁻ cotransporter (NCC) in the distal convoluted tubule, so more sodium, chloride and water leave in the urine. The extra sodium reaching the collecting duct increases potassium loss, and calcium reabsorption rises. The IV form acts within minutes, which helps when oral treatment is not possible.
- Chlorothiazide blocks NCC in the distal tubule
- Sodium, chloride and water are lost in the urine
- Potassium is lost downstream; calcium is kept
- IV form: fast diuresis when oral use is not possible
Pharmacokinetics
- Metabolism
- Not metabolised
- Elimination
- Eliminated quickly and almost entirely unchanged by the kidney
- Half-life
- 45 to 120 minutes in plasma
- Onset and duration
- By mouth: diuresis within 2 hours, lasting about 6 to 12 hours; IV: within about 15 minutes
Indications
- Oedema from heart failure, as an adjunct Heart failure →
- Oedema from cirrhosis or from corticosteroid or oestrogen therapy Cirrhosis →
- High blood pressure (oral form) Arterial hypertension →
Adverse effects
Common
- Hypokalaemia and hyponatraemia
- High uric acid and glucose
- Dizziness on standing
- Photosensitivity and rash
- Blood in the urine after IV use
Contraindications
- Anuria
- Hypersensitivity to chlorothiazide or other sulfonamide-derived drugs
Key interactions
- Lithium
- Less lithium clearance and risk of toxicity
- Digoxin
- Hypokalaemia increases digoxin toxicity
- Corticosteroids
- More potassium loss
- Whole blood or blood derivatives
- Not given at the same time through the same line
What is monitored
- Potassium and sodium
- Kidney function
- Blood pressure
- Glucose and uric acid
Administration and safety
- IV form: given slowly by direct injection or infusion; extravasation must be avoided, and it is never given IM or subcutaneously.
- Compatible with dextrose or sodium chloride infusions; not given together with blood or blood products.
- IV use in infants and children is limited and generally not recommended.
Nursing care
- Before giving: blood pressure, potassium and kidney function.
- Check the IV site during and after injection; stop at the first sign of leakage.
- Watch for weakness, cramps or irregular pulse (low potassium), especially with digoxin.
- Teach: rise slowly, protect the skin from the sun.
Pregnancy and breastfeeding
Used only for oedema from pathological causes; thiazides cross the placenta.
Test yourself
Think of the answer, then tap the question to see it.
What sets chlorothiazide apart from hydrochlorothiazide in practice?
It is available as an IV injection, which acts within minutes when oral therapy is not possible.
Why must extravasation of IV chlorothiazide be avoided?
The IV solution injures tissue if it leaks; for the same reason it is never given IM or subcutaneously.
Which transporter does chlorothiazide block?
The Na⁺-Cl⁻ cotransporter (NCC) of the distal convoluted tubule.
Related drugs
Related conditions
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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 - CHLOROTHIAZIDE SODIUM injection, powder, lyophilized, for solution (DailyMed (U.S. National Library of Medicine), 2026); Chlorothiazide: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2017); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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