Mannitol is a nonelectrolyte of low molecular weight that acts as an osmotic diuretic.
It is pharmacologically inert and hence can be administered in large quantities to raise the osmolarity of plasma and tubular fluid.
It is metabolized in the body minimally, freely filtered at the glomerulus, and undergoes limited reabsorption.
Mechanism of action.
Mannitol limits tubular water and electrolyte reabsorption by:
- Retaining water isoosmotically in the proximal tubules by diluting the luminal fluid, which opposes NaCl reabsorption.
- Increases renal blood flow, especially to the medulla; hence, passive salt reabsorption reduces.
- Inhibits transport processes in the thick ascending LOH.
- Expand extracellular fluid volume, increasing the glomerular filtration rate and inhibiting renin release.
Clinical uses.
- Management of chronic edema or used as a natriuretic.
- Increase intracranial or intraocular tension in acute congestive glaucoma, head injury, or stroke.
- Maintain glomerular filtration rate and urine flow in impending acute renal failure, i.e., shock, severe trauma, cardiac surgery, or hemolytic reactions.
- To counteract low osmolality of plasma due to rapid hemodialysis or peritoneal dialysis.
Adverse effects.
- Expansion of blood volume.
- Headache, chills, or fever.
- Chest pain, fast heartbeat
- Nausea and vomiting
- Hypersensitivity and thrombophlebitis at the injection site.
- Swelling of feet.
Contraindication.
- Anuria
- Acute tubular necrosis
- pulmonary edema
- Congestive heart failure.
- acute left ventricular failure,
- cerebral hemorrhage.
