Osmotic diuretics

Osmotic diuretics

Osmotic diuretics cause diuresis through osmosis, moving fluid into the extracellular spaces. They include mannitol and urea.

Pharmacokinetics

Administered I.V. for rapid distribution, osmotic diuretics are freely filtered by the glomeruli of the kidney’except for mannitol, which is only slightly metabolized. Osmotic diuretics are excreted primarily in urine.

Pharmacodynamics

Osmotic diuretics receive their name because they increase the osmotic pressure of the glomerular filtrate, which inhibits the reabsorption of sodium and water. They create an osmotic gradient in the glomerular filtrate and the blood. In the glomerular filtrate, the gradient prevents sodium and water reabsorption. In the blood, the gradient allows fluid to be drawn from the intracellular into the intravascular spaces.

Pharmacotherapeutics

Osmotic diuretics are used to treat acute renal failure and cerebral edema and to reduce intracranial and intraocular pressure. Mannitol is used to promote diuresis in acute renal failure and to promote urinary excretion of toxic substances.

Drug interactions

Taking osmotic diuretics with lithium may increase renal excretion of lithium, which in turn decreases the effectiveness of lithium. Patients taking both drugs require lithium level monitoring.

Warning!

Adverse reactions to osmotic diuretics

Adverse reactions to osmotic diuretics include:

• hyponatremia
• dehydration
• circulatory overload (from osmotic effects)
• thrombophlebitis or local irritation at the infusion site