Diuretics Notes

Lecture 16

Diuretics

• General

  • Classified in 5 groups

    • OSMOTIC

    • CARBONIC ANHYDRASE INHIBITORS

    • LOOP

    • THIAZIDES

    • POTASSIUM SPARING

  • Why diuretics?

    • Heart failure

      • Activation of rennin-angiotensin system

      • Retention of sodium and water/increase in blood volume

      • Elevated venous pressure- pulmonary and systemic oedema

    • Hypertension

      • High renin-angiotensin release and vasoconstriction, aldosterone secretion and salt retention

      • Low renin-sodium retention due to increased sympathetic adrenergic activity or a defect in sodium-couple calcium transport

    • Other oedema

      • Renal-nephrotic syndrome, renal failure

      • Liver failure

• OSMOTIC DIURETICS- MANNITOL, UREA

  • Elevate osmotic pressure of glomerular filtrate to an extent that tubular reabsorption of water and solutes (mainly Na) are hindered

  • Mannitol

    • Indications

      • Oliguric acute renal failure

      • During CVS surgery

      • Reduction of intracranial pressure prior to and during neurosurgery

      • During any surgery for patients with poor renal function

      • Treat acute toxicities with so drugs such as barbiturates, salicylates, imipramine

      • Treat oedema & ascitis of nephrotic, cirrhotic, and cardiac origin

    • Precautions and contraindications

      • Patients with shock & oliguria: mannitol should not be given until fluid, plasma, blood, and electrolytes have been replaced

      • It is contraindicated in well established renal failure

        • A test dose is usually given before use

• CARBONIC ANHYDRASE INHIBITORS- ACETAZOLAMIDE

  • General

    • Inhibit renal tubule enzyme = less HCO3 out PCT= less Na reabsorption

    • Rapid tolerance to diuretic action occurs as a result of reduction in HCO3 in blood leading to metabolic acidosis which rapidly reverses diuretic effect

  • Indications

    • Weakest diuretics- seldom used in CVS disease

    • Treat glaucoma

    • Only acetazolamide used for

      • Prophylaxis for altitude sickness; Anticonvulsant; Barbiturates & sallacytes toxicity

  • Precautions and adverse effects

    • Renal disorders such as renal colic, calculi and crystal urea are possible

    • Caution in those with pulmonary disease (infection, obstruction, acidosis)

    • Caution with haematologic diseases, may induce bone marrow suppression

• LOOP DIURETICS- FUROSEMIDE

  • General

    • Inhibit Na, K and Cl co-transport in thick ascending limb

    • Reduce renal Ca reabsorption, thus used to treat hypercalcaemia

    • Induce renal synthesis of prostaglandins- increase renal blood flow

  • Indications

    • High efficiency loop diuretics/High ceiling diuretics

    • Heart failure

    • Hypertension

    • Impaired renal function

  • Precautions and contraindications

    • Electrolyte imbalance

    • Impaired hepatic function patients: used with...

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