Non-Diuretic Uses of Diuretics

Non-Diuretic Uses of Diuretics

1. Definition, scope & conceptual framework

• Scope of this topic — the extra-renal / therapeutic uses of diuretic drugs that do not depend on their natriuretic (salt-losing) action: acetazolamide for glaucoma, mountain sickness, epilepsy and CSF disorders; thiazides for nephrogenic diabetes insipidus (NDI) and calcium-stone/hypercalciuria; loop diuretics for acute hypercalcaemia and hyperkalaemia; mannitol for raised intracranial and intraocular pressure; aldosterone antagonists for heart failure, resistant hypertension and hyperaldosteronism; amiloride for lithium-NDI and Liddle syndrome. The primary natriuretic pharmacology and classification of diuretics is deliberately out of scope here (Katzung 16e Ch.15, pp.266–81).
• Terminology needed to reason about these uses — a diuretic increases urine volume; a natriuretic increases renal Na⁺ excretion; an aquaretic increases excretion of solute-free water. Osmotic agents (mannitol) and ADH antagonists are aquaretics, not directly natriuretic — their therapeutic value in raised ICP/IOP flows from the osmotic water shift, not from salt loss (Katzung 16e Ch.15, p.261).
• Why a "diuretic" can have non-diuretic uses — the unifying idea — most diuretic targets (carbonic anhydrase, NKCC2, NCC, ENaC, the mineralocorticoid receptor) exist in extra-renal tissues too (ciliary body, choroid plexus, inner ear, myocardium, vasculature, brain), and several renal actions have downstream systemic consequences (Ca²⁺ handling, water handling, aldosterone antagonism). The therapeutic "side channel" of each class is therefore predictable from where else its molecular target is expressed (Katzung 16e Ch.15, pp.266–7; KDT 8e Ch.42, p.633).
• Two mechanistic patterns run through the topic: (1) an extra-renal enzyme/receptor is inhibited (acetazolamide on ciliary-body & choroid-plexus carbonic anhydrase; spironolactone on cardiac/vascular mineralocorticoid receptors); (2) a renal action produces a paradoxical or exploited systemic effect (thiazide-induced volume contraction → antidiuresis in NDI; thiazide-enhanced distal Ca²⁺ reabsorption → hypocalciuria; loop-induced abolition of the TAL lumen-positive potential → calciuresis in hypercalcaemia) (Katzung 16e Ch.15, pp.271–2, 280; KDT 8e Ch.42, pp.627, 631).
• Historical note anchoring the "non-diuretic" framing — carbonic anhydrase inhibitors were the forerunners of modern diuretics (discovered 1937 when bacteriostatic sulfonamides were noticed to cause alkaline diuresis and hyperchloraemic acidosis); with more powerful agents available, acetazolamide is now rarely used as a diuretic and survives almost entirely on its non-diuretic indications (Katzung 16e Ch.15, pp.266, 267; KDT 8e Ch.42, p.632).

A. Carbonic anhydrase inhibitors — acetazolamide