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Diuretics: Part 1 - Mechanisms and Types

Explore the pharmacology of diuretics, including their mechanisms of action and classifications. Learn about carbonic anhydrase inhibitors, loop diuretics, thiazide diuretics, potassium-sparing diuretics, and osmotic diuretics. Understand how these drugs affect renal function and their therapeutic uses and potential adverse effects.

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Diuretics: Part 1 - Mechanisms and Types

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  1. DIURETICSPart 1 Prof. Hanan Hagar Dr.Abdul latif Mahesar Pharmacology Unit

  2. Diuretics • Are drugs that increase renal excretion of sodiumand water resulting in increase in urine volume. • Diuresis: is the process of excretion of water in the urine. • Natriuresis:  is the process of excretion of sodium in the urine .

  3. Mechanism of actions of diuretics • Most diuretics act by interfering with the normal sodium reabsorptionby the renal tubules resulting into sodium and water excretion.

  4. Normal Sodium Re-absorption

  5. Site of action of diuretics

  6. Normal Sodium Re-absorption

  7. Sites of action for diuretics How diuretics produce their effects? • Target molecules for diuretics are carriers or transportersin luminal membrane of renal tubular cells required for tubular reabsorption of sodium from filtrate back into blood.

  8. Types of diuretics

  9. Site of action of diuretics

  10. Classification of diuretics • Carbonic anhydrase inhibitors • Loop diuretics • Thiazide diuretics • Potassium-sparing diuretics • Osmotic diuretics

  11. Carbonic anhydrase inhibitors Thiazide diuretics Loop diuretics K-sparing diuretics

  12. Ascending loop of Henle

  13. Distal convoluted tubules (DCT)

  14. COLLECTING TUBULES (CT)

  15. COLLECTING TUBULES (CT)

  16. Carbonic Anhydrase Inhibitors

  17. Carbonic Anhydrase Inhibitors Acetazolamide – dorzolamide Mechanism of action: Site of action: proximal convoluted tubules Inhibits carbonic anhydrase (CA) enzyme in proximal convoluted tubules thus interferes with NaHCO3 re-absorption and causes diuresis.

  18. Carbonic Anhydrase Inhibitors CA is required for reversible reaction, in which CO2 +H2O H2CO3 H+ HCO3-

  19. carbonic anhydrase Lumen Blood Luminal membrane Basolateral membrane

  20. Blood Lumen Basolateral membrane Luminal membrane Proximal tubules

  21. Pharmacokinetics: • given orally once a day. • Onset of action is rapid (30 min). • Duration of action (12 h). • Excreted by active secretion in proximal convoluted tubules. • Produces alkaline urine

  22. Pharmacological actions: • ↑ urine volume mildly • ↑ urinary excretion of sodium, potassium , bicarbonate (alkaline urine). • Metabolic acidosis. • ↑ Urinary phosphate excretion. • Promotes K+ excretion by ↑the load of Na+ delivered to the distal tubules.

  23. Why do CA inhibitors have weak diuretic properties? Diuretic properties decreases after several days as the blood bicarbonate falls.

  24. Therapeutic uses: • Open angle glaucoma carbonic anhydrase inhibitors cause ↓ IOP by reducing aqueous humor formation in ciliary body of eye. • As prophylactic therapy, in acute mountain sickness ↓ CSF of brain given nightly 5 days before the ascent ↓ weakness, breathlessness , dizziness, nausea, cerebral & pulmonary oedema. IOP: Intraocular pressure; CSF: Cerebrospinal fluid

  25. Therapeutic uses: • Epilepsy (decrease cerebrospinal fluid, CSF). • Urinary alkalinization to enhance renal excretion of acidic substances (cysteine in cystinuria). • Hyperphosphatemia • Metabolic alkalosis

  26. Adverse effects: • Hypokalemia (potassium loss). • Metabolic acidosis. • Renal stone formation (calcium phosphate stones). • Hypersensitivity reaction.

  27. Dorzolamide • Is a carbonic anhydrase inhibitor • Used topically for treatment of open-angle glaucoma. • no diuretic or systemic side effects (Why?)

  28. Osmotic diuretics 60–80%

  29. Osmotic diuretics Mannitol: • Poorly absorbed • If given orally osmotic diarrhea • Given intravenously • Not metabolized • Excreted by glomerular filtration without being re-absorbed or secreted within 30-60 min

  30. Mannitol • Acts in proximal tubules & descending loop of Henle by osmotic effect. • Mannitol, IV, water excretion with relatively less effect on Na+ (water diuresis). • Expand the extracellular fluid volume, decrease blood viscosity, and inhibit renin release, ↑renal blood flow.

  31. Mannitol increases urine output by osmosis, drawing water out of cells and into the blood stream.

  32. Therapeutic Uses: • Acute renal failure due to shock or trauma (maintain urine flow- preserve kidney function). • In acute drug poisoning: To eliminate drugs that are reabsorbed from the renal tubules e.g. salicylates, barbiturates. • To  intracranial & intraocular pressure before ophthalmic or brain procedures (cerebral edema).

  33. Adverse Effects: • Headache, nausea, vomiting • Extracellular volume expansion, complicates heart failure & pulmonary oedema • Excessive use dehydration & hypernatraemia (Adequate water replacement is required).

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