Pharm Diuretics

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diuretics

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Substances increase urine output
Act on kidney:
Directly or indirectly

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5 classes of diuretics

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Thiazide diuretics
Loop diuretics
Potassium sparing diuretics
Osmotic diuretics
Carbonic anhydrase (CA) inhibitors

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Thiazide Diuretics: site

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DCT

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Thiazide Diuretics: mech

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↓ NaCl co‐transport → ↓ NaCl reabsorption →
water stays in urine

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Thiazide Diuretics: population

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Gentle diuresis → safe in the elderly

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Thiazide Diuretics: adverse

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– Hypokalemia (common)
– Hyperglycemia
– Hypercalcemia
– Hypercholesterolemia
– Hyperuricemia (→ gout)

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Thiazide Diuretics: example

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Hydrochlorothiazide

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Loop Diuretics: site

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Thick segment of the ascending limb of loop of
Henle

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Loop Diuretics: mech

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– ↓ Na‐K‐2Cl co‐transport→↓ NaCl reabsorption →
water stays in urine
– ↑ Ca2+ and Mg2+ excretion

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Loop Diuretics: characteristic

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strong

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Loop Diuretics: adverse

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– Similar to thiazides +
– Hypocalcemia→osteoporosis
– Ototoxicity deafness (rare)

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Loop Diuretics: example

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furosemide, bumetanide, ethacrynic acid

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Potassium Sparing Diuretics: site

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– DCT (late segment) and collecting ducts

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Potassium Sparing Diuretics: mech

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– NaCl and water loss in urine
– K+ sparing

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Potassium Sparing Diuretics: adverse

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– Hyperkalemia
– Androgen or estrogen‐like effects (spironolactone)

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Potassium Sparing Diuretics: Aldosterone

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– Hormone
– Acts on DCT & collecting ducts
– Activated via RAS

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Potassium Sparing Diuretics: Aldosterone antagonists

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– Competitive inhibition of aldosterone at the
receptor site
– E.g., spironolactone

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Potassium Sparing Diuretics: Sodium channel blockers

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– ↓ Na+ reabsorption → water stays in urine
– Weak diuretics
– E.g., amiloride – triamterine

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Osmotic Diuretics: site

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– Throughout the nephron specially PCT

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Osmotic Diuretics: mech

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– Filtered in glomeruli & cannot be reabsorbed from
renal tubules →remain in tubular lumen →
– ↑ osmolarity of tubular fluid → retains water in urine

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Osmotic Diuretics: other actions

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– ↓ intracranial pressure
– ↓ intraocular pressure

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Osmotic Diuretics: adverse effects

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– ↑ ECF volume →
– May aggravate HF and pulmonary edema

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Osmotic Diuretics: example

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mannitol

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Carbonic Anhydrase Inhibitors: site

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PCT

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Carbonic Anhydrase Inhibitors: mech

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– ↓ CA enzyme → ↓ H+ excretion → ↑ Na+ and K+
excretion

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Carbonic Anhydrase Inhibitors: adverse

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– Metabolic acidosis
– Hypokalemia

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Carbonic Anhydrase Inhibitors: example

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acetazolamide

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Therapeutic Uses of Diuretics

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• Edema
• Hypertension
• Heart failure
• Others:
– Glaucoma (CA inhibitors, osmotic diuretics)
– ↑ intracranial pressure (osmotic diuretics)

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Diuretics & Potassium

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• K+‐losing duretics:
– Thiazide and loop diuretics
– Cause hypokalemia
– Require K+ supplements
• K+‐sparing diuretics:
– Cause hyperkalemia
• A combination is helpful:
– E.g., amiloride + hydrochlorothiazide

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Diuretics & Calcium

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• Ca2+‐sparing diuretics:
– ↓ Ca excretion in urine → hypercalcemia
– Include thiazide diuretics
• Ca2+‐losing diuretics:
– ↑ Ca excretion in urine →hypocalcemia
– Include loop diuretics

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Diuretic Resistance

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• ↑ proximal reabsorption of Na+
• ↓ GFR due to low cardiac output
– E.g., heart failure (improved by digitalis)
• Impaired secretion into tubule lumen
• Non‐compliance
• Aspirin‐like drugs (NSAIDs)
• Activation of RAS