Osmotic diuretics

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Osmotic diuretics


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Osmotic diuretics

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mannitol and p. 631

Mannitol p. 631

extracellular volume and p. 605

site of action p. 631

Pulmonary edema

mannitol p. 631


Diuretics are medications that act on the kidneys to increase production of urine, and therefore, elimination of water from the body.

There are 5 main types of diuretics: carbonic anhydrase inhibitors; loop diuretics; thiazide and thiazide-like diuretics; potassium sparing diuretics; and last but not least, osmotic diuretics - which we’ll get intimately acquainted with during this video.

Now, the basic unit of the kidney is called a nephron, and each nephron is made up of a glomerulus, which filters the blood. The filtered content goes through the renal tubule, where excess waste, and molecules (such as ions and water), are removed or filtered through an exchange between the tubule and the peritubular capillaries. So the renal tubule plays a huge role in secretion and reabsorption of fluid and ions - such as sodium, potassium, and chloride - in order to maintain homeostasis - or the the balance of fluid and ions in our body.

The renal tubule has a few segments of its own: the proximal convoluted tubule; the U-shaped loop of Henle, with a thin descending, a thin ascending, and a thick ascending limb; and finally, the distal convoluted tubule, which empties into the collecting duct, which collects the urine.

The prototypal osmotic diuretic is mannitol; other osmotic diuretics like glycerin and isosorbide are rarely used.

Following IV administration, mannitol travels through the bloodstream and acts like you’d expect an osmotically active molecule to act: it sucks water out of the cells it encounters along the way, and all that extra water reaches the kidneys as increased renal blood flow.


Diuretics are a class of drugs used to reduce the amount of water in the body, by raising the production of urine. Once filtered in the glomerulus, osmotic diuretics do not get reabsorbed. This increases the osmotic pressure in the kidneys and causes water to leave blood into the forming urine. The main effect of osmotic diuretics is applied in parts of the nephron that are permeable to water, mainly the proximal tubule, descending part of the loop, and the collecting tubules. Examples of osmotic diuretics include mannitol, glycerin, and isosorbide.


  1. "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "Diuretics in acute kidney injury" Minerva Anestesiol (2009)
  5. "Inhaled mannitol for cystic fibrosis" Cochrane Database of Systematic Reviews (2018)
  6. "Sodium Glucose Cotransporter-2 Inhibition in Heart Failure" Circulation (2017)

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