Description: Mannitol is a parenteral osmotic diuretic. It is used to reduce intracranial pressure, cerebral edema, and intraocular pressure, and to promote diuresis in the prevention and/or treatment of oliguria in patients with acute renal failure. It is used as an additional measure in the supportive treatment of edema of various origins. Mannitol is also used alone or in combination with other diuretic agents to promote urinary excretion of toxins such as salicylates, barbiturates, lithium, and bromides. A phase III trial is currently underway to assess the effectiveness of mannitol (Aridol&#174 in identifying exercise-induced bronchoconstriction in subjects suspected of having asthma. Mannitol was approved by the FDA in 1944.

Mechanism of Action: Systemically, mannitol elevates blood osmolality, which increases the osmotic gradient between blood and tissues, thereby facilitating the flow of fluid out of tissues, including the brain and eye, and into the interstitial fluid and blood. This activity reduces cerebral edema, intracranial pressure, cerebrospinal fluid pressure, and intraocular pressure. Reabsorption of mannitol by the kidney is minimal, so the osmotic pressure of the glomerular filtrate increases, inhibiting the reabsorption of water and solutes in the renal tubule, and producing diuresis. This activity may reverse the acute reductions in renal blood flow, GFR, and urine flow associated with trauma. In addition, this effect can enhance the urinary excretion of toxins and protect against renal toxicity by preventing the concentration of toxins in the tubule, although enough renal blood flow and GFR must exist to enable the drug to reach the tubule and exert its effect.

Pharmacokinetics: Mannitol is administered intravenously, and diuresis generally occurs in 1—3 hours. A decrease in the cerebrospinal fluid pressure will occur in approximately 15 minutes and will persist for 3—8 hours after the infusion is stopped. Elevated intraocular pressure can be reduced in 30—60 minutes, and the effect can last for 4—8 hours. Mannitol remains confined to the extracellular compartment and does not appear to cross the blood-brain barrier unless very high concentrations exist or the patient has acidosis. It is not known if mannitol is distributed into breast milk. The drug undergoes minimal (if any) metabolism to glycogen in the liver. The majority of a dose is freely filtered by the kidneys, with less than 10% tubular reabsorption. The half-life of mannitol ranges from 15—100 minutes. In patients with acute renal failure or other conditions affecting the GFR, however, the half-life can be increased to 36 hours.

Drug Information Provided by
Gold Standard, Inc. � 2007