Chlorthalidone
- Class: Thiazide-like diuretic
- Used for: high blood pressure
- Say it: klor-THAL-ih-dohn
- Forms: tablet
It is thiazide-like rather than a true thiazide, blocking the same sodium-chloride transporter in the distal tubule — but with a half-life of 40-60 hours against hydrochlorothiazide's 6-15.
Side effects
Common: low potassium, frequent urination, gout flare
Serious: low sodium
Typical dose
12.5–25 mg once daily
Roughly 1.5 to 2 times as potent as hydrochlorothiazide milligram for milligram, and far longer-acting — so 25 mg here is not 25 mg there.
Check yourself
What is the main advantage of chlorthalidone over hydrochlorothiazide?
- A much longer duration of action, holding blood pressure down overnight
- It does not lower potassium
- It acts at the loop of Henle instead
- It is safe in severe renal impairment
Show answer
A. A much longer duration of action, holding blood pressure down overnight
Both block the same distal tubule transporter. Chlorthalidone simply persists three to four times longer, which is why it controls 24-hour pressure better — and also why its electrolyte effects are stronger, not weaker.
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