Question

Consider the following:
1. Metolazone
2. Amiloride
3. Triamterene
4. Chlorthalidone
Which of these are the potassium sparing diuretics?

• A. 1, 2 and 3
• B. 1, 2 and 4
• C. 2 and 3
• D. 1, 3 and 4

Hint:

Amiloride and triamterene block sodium channels in the collecting duct.

Answer 1

The Correct Option is C

This question sorts four diuretics into those that spare potassium and those that waste it.

1. Metolazone: A thiazide-like drug that works on the distal tubule and causes the body to lose potassium, so it is not potassium sparing.
2. Amiloride: Blocks sodium channels in the collecting duct, cutting sodium reabsorption while leaving potassium alone. This is a true potassium sparing diuretic.
3. Triamterene: Acts through the same sodium channel blocking route as amiloride, so it is grouped with it as potassium sparing.
4. Chlorthalidone: Another thiazide-like drug, closely related to hydrochlorothiazide, and it also wastes potassium rather than sparing it.

Only amiloride and triamterene work through the collecting duct mechanism that protects potassium, while metolazone and chlorthalidone both work upstream in a way that loses potassium.

Let's summarize:

• Amiloride and triamterene block sodium channels in the collecting duct and spare potassium.
• Metolazone and chlorthalidone are thiazide-like drugs that waste potassium.

So the potassium sparing diuretics here are amiloride and triamterene, meaning statements 2 and 3 are correct.