Pharmacology of major drug classes used - diuretics

Classes

Three major classes act at different nephron segments, with correspondingly different potency and clinical roles

Among the most commonly prescribed cardiovascular drug classes, spanning acute decongestion to chronic hypertension management

Class	Site	Example	Potency	Main use
Loop diuretics	Thick ascending limb (Na-K-2Cl transporter)	Furosemide	Most potent	Acute/chronic fluid overload, heart failure
Thiazides	Distal convoluted tubule (Na-Cl transporter)	Hydrochlorothiazide, indapamide	Moderate	Hypertension (first-line), mild fluid states
Potassium-sparing/MRA	Collecting duct	Spironolactone, eplerenone	Mild diuretic, but prognostically important in HF	Heart failure (mortality benefit), resistant hypertension, hyperaldosteronism

Loop diuretics lose efficacy as eGFR falls but remain effective even in advanced CKD (unlike thiazides, which become largely ineffective below eGFR ~30) - a key prescribing distinction
MRAs (spironolactone, eplerenone) provide a mortality benefit in HFrEF, distinct from their diuretic effect - part of foundational four-pillar HF therapy, not just add-on diuresis
Electrolyte monitoring: loop/thiazide -> hypokalaemia, hyponatraemia (thiazides especially); MRA -> hyperkalaemia (particularly with concurrent ACEi/ARB or renal impairment)

Heart failure, hypertension, resistant hypertension (spironolactone add-on), primary hyperaldosteronism

Thiazide efficacy declining with worsening renal function is a common source of "diuretic resistance" that is actually a class/dosing problem, correctable by switching to or adding a loop diuretic

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