Osmotic Diuretics - Cardiovascular Poison

Osmotic Diuretics

·              Osmotic diuretics act (primarily in the loop of Henle and secondarily in the proximal tubule), as non-reabsorbable solutes thereby limiting the osmosis of water into the interstitial space. By extracting water from intracellular compartments, they expand extracellular fluid volume, decrease blood viscocity, and inhibit renin release. They increase the urinary excretion of nearly all electrolytes—sodium, potassium, calcium, magne-sium, chloride, bicarbonate, and phosphate.

·              Commonly used osmotic diuretics include mannitol, glyc-erine, isosorbide, laevulose, and urea. Of these, glycerine and isosorbide are active orally, while the others are not and must be given intravenously.

Uses

Treatment of

■■   Acute tubular necrosis

■■ Dialysis disequilibrium syndrome

■■ Glaucoma

■■   Cerebral oedema.

Adverse Effects and Toxic Features

·      Pulmonary oedema may be precipitated in patients with heart failure or pulmonary congestion.

·      Other adverse effects include hyper- or hyponatraemia, headache, nausea, vomiting, and dehydration.

·      Glycerine can cause hyperglycaemia.

·      Mannitol has caused fatal colonic perforation when used orally as a purgative. It has also been implicated in the development of renal failure in several case reports.