Osmotic Diuretics

Question 1

Where do osmotic diuretics exert their effects?

Answer 1

The proximal tubule (~65%)

Question 2

Benefits of osmotic diuretics?

Answer 2

Helps to eliminate intracellular volume

Question 3

Mannitol (Osmitrol)

Answer 3

prototype for osmotic diuretics; also used –> urea, glycerin, and isosorbide

Question 4

MOA of Mannitol?

Answer 4

• non-metabolized 6-C sugar; freely filtered w/ minimal absorption
• Inability to reabsorb the solute keeps water in the PT lumen; this water is delivered to the distal portion of the nephron where much of it is excreted.
• Acts throughout the body to pull water out of cells
• Net effect after administration is to excrete total body water in excess of plasma electrolytes

Question 5

PK of mannitol?

Answer 5

Distributes in EC fluid, must give IV in large amounts sufficient to raise its osmolality (eg 50-200 grams over 24 hours)

• Effects are noticeable within 30-60 minutes, and is eliminated unchanged in urine over 6-8 hrs

Question 6

Adverse effects of osmotic diuretics?

Answer 6

• EC volume is acutely ↑ bc mannitol sucks water out of cells –> can exacerbate HF
• HA, nausea, vomiting, and fluid & electrolyte imbalance can occur

Question 7

Therapeutic uses of mannitol?

Answer 7

• Prophylaxis of RF, keeps some fluid volume in the tubules to prevent them from collapsing when the GFR is very low
• Reduction of intracranial pressure
• Reduction of intraocular pressure (trx glaucoma) when pts don’t respond to other therapy