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Nursing Pharmacology Chapter 26: Renal Pharmacology
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Introduction
Osmotic diuretics cause water to be retained within the proximal tubule and descending limb of loop of Henle (freely permeable to water)
Mannitol (Osmitrol) is an example of osmotic diuretic.
Clinical Use: mainly used to reduce increased intracranial pressure;
Osmotic diuretics: properties
Mannitol (Osmitrol) : not metabolized, freely filtered at the glomerular
Usually administered by IV; oral administration results in an osmotic diarrhea-- perhaps useful to promote elimination of toxic substances from the GI tract (in conjunction with activated charcoal)
Urine volume increases with mannitol excretion due to direct osmotic effects
Sodium reabsorption is reduced because of increased urine flow rates {decreased contact time between urine and tubular epithelial cells}
To increase urine volume:
May be used to prevent anuria if the kidney due to hemolysis or rhabdomyolysis is presented with a large pigmented load.
When renal hemodynamics are compromised
To decrease intracranial or intraocular pressure:
Mannitol (Osmitrol) extract water from intracellular compartments, reducing total body water
Following IV administration, intracranial pressure falls within 60-90 minutes.
Volume expansion effects -- increased extra cellular fluid volume and hyponatremia may cause pulmonary edema, complicating congestive heart failure
Headache, nausea, vomiting -- commonly observed
Dehydration and hypernatremia:
Fluid loss leads to significant dehydration and in the absence of adequate fluid replacement leads to hypernatremia.
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Jackson, E.K. Diuretics In, Goodman and Gillman's The Pharmacological Basis of Therapeutics, (Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp. 685- 713
Jackson, E.K. Vasopressin and Other Agents Affecting the Renal Conservation of Water In, Goodman and Gillman's The Pharmacological Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp.715-732
Ives, H.E., Diuretic Agents, in: Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 242-259.
