Diuretics: Where They Work, What They Do to Potassium
Every diuretic is defined by one spot on the nephron. That spot sets how much sodium the drug can dump — and which way the patient's potassium moves. Tap a site on the tubule, or pick a class.
The nephron
Filtered Na⁺ excreted—
Effect on serum potassium
Four classes, four sitestap one to begin
One tubule, four doorsFiltrate travels the nephron in order: proximal tubule → descending limb → thick ascending limb → distal tubule → collecting duct. Each segment reclaims a different share of the filtered sodium, so a drug's potency is decided before it is ever dosed — by where on that path it lands.
The earlier and the busier the segment, the more sodium a drug can dump. The thick ascending limb reabsorbs the biggest slice, so the drug that blocks it is the strongest — and the collecting duct handles the smallest, so the drug that blocks it is the weakest.
Class
Site of action
Na⁺ out
Serum K⁺
Tap any row to open that class.
Three of the four waste potassium. One hoards it. Loop, thiazide and osmotic all drive K⁺ down; only the potassium-sparing class drives it up. That single split decides whether you reach for a potassium supplement — or lock it away.
Loop and thiazide diuretics lower potassium by the same trick: they let extra sodium reach the collecting duct, where it is traded for potassium that then leaves in the urine. Potassium-sparing drugs work at that very trade — which is exactly why they are so often added to a loop or thiazide rather than used alone.