Non-Diuretic Uses of Diuretics

Introduction & unifying concept

• Scope — The extra-renal / therapeutic uses of diuretic drugs that do not depend on their natriuretic (salt-losing) action — a recurring RGUHS 10-mark question. The primary natriuretic pharmacology and classification of diuretics is deliberately out of scope here.
• Terminology — A diuretic increases urine volume; a natriuretic increases renal Na⁺ excretion; an aquaretic increases excretion of solute-free water. Osmotic agents (mannitol) act as aquaretics — their value in raised ICP/IOP comes from the osmotic water shift, not salt loss.
• Why a diuretic has non-diuretic uses — Most diuretic targets (carbonic anhydrase, NKCC2, NCC, ENaC, the mineralocorticoid receptor) are also expressed in extra-renal tissues (ciliary body, choroid plexus, myocardium, vasculature, brain), and several renal actions have downstream systemic consequences (Ca²⁺/water handling, aldosterone antagonism).
• Two mechanistic patterns — (1) An extra-renal enzyme/receptor is inhibited (acetazolamide on ciliary-body & choroid-plexus CA; spironolactone on cardiac/vascular MR); or (2) a renal action produces a paradoxical or exploited systemic effect (thiazide volume contraction → antidiuresis in NDI; loop abolition of the TAL lumen-positive potential → calciuresis).