Osmotic diuretic

An osmotic diuretic is a type of diuretic that inhibits reabsorption of water and sodium (Na). They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate.[1] This fluid eventually becomes urine.

Two examples are mannitol[2] and isosorbide.

In the nephron, osmotic diuretics act at the portions of the nephron that are water-permeable.[3]

Osmotic diuretics work by expanding extracellular fluid and plasma volume, therefore increasing blood flow to the kidney. This washes out the cortical medullary gradient in the kidney. This stops the loop of Henle from concentrating urine, which usually uses the high osmotic and solute gradient to transport solutes and water.

These agents can also act at other parts of the body. For example, they can be used to reduce intracranial[4] and intra-ocular pressure. Osmotic diuretics increase plasma volume, but because they do not cross the blood-brain barrier, this does not affect the nervous system. In effect, this is the cause of their action reducing locally the plasma volume in the nervous system.

  1. ^ "osmotic diuretic" at Dorland's Medical Dictionary
  2. ^ "Mannitol". Retrieved 2008-12-20.
  3. ^ Trevor, Anthony J.; Katzung, Bertram G. (2003). Pharmacology. New York: Lange Medical Books/McGraw-Hill, Medical Publishing Division. p. 46. ISBN 0-07-139930-5.
  4. ^ Sakowitz OW, Stover JF, Sarrafzadeh AS, Unterberg AW, Kiening KL (February 2007). "Effects of mannitol bolus administration on intracranial pressure, cerebral extracellular metabolites, and tissue oxygenation in severely head-injured patients". J Trauma. 62 (2): 292–8. doi:10.1097/01.ta.0000203560.03937.2d. PMID 17297315.