Metolazone
- Class: Thiazide-like diuretic
- Used for: fluid overload
- Say it: meh-TOH-luh-zohn
- Forms: tablet
Most thiazides stop working below an eGFR of about 30; metolazone keeps going. Given half an hour before a loop diuretic it produces sequential nephron blockade, a far larger diuresis than either drug alone.
Side effects
Common: low potassium, dizziness, dehydration
Serious: severe salt loss with a loop diuretic
Typical dose
2.5–5 mg once daily
Give it 30 minutes before the loop diuretic, not with it — the timing is what produces the combined effect.
Check yourself
Why is metolazone added to furosemide rather than used on its own?
- It blocks the distal site that would otherwise reabsorb the sodium escaping the loop
- It makes furosemide last longer in the blood
- It protects the kidney from furosemide toxicity
- It replaces the potassium that furosemide loses
Show answer
A. It blocks the distal site that would otherwise reabsorb the sodium escaping the loop
A loop diuretic dumps sodium into the distal tubule, which simply takes much of it back — diuretic braking. Blocking that second site is what breaks the resistance, and it is also why the electrolyte losses become so steep.
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