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Mannitol or hexan-1,2,3,4,5,6-hexol (C6H8(OH)6) is an osmotic diuretic agent and a weak renal vasodilator. It is a sorbitol isomer.
Chemical properties
Chemically, mannitol is an alcohol and a sugar, or a polyol; it is similar to xylitol or sorbitol. However, mannitol has a tendency to lose a hydrogen ion in aqueous solutions, which causes the solution to become acidic. For this reason, it is not uncommon to add a substance to adjust its pH, such as sodium bicarbonate.
Uses
Mannitol is used mainly to reduce intracranial pressure in the cranium and to treat patients with oliguric renal failure. It is administered intravenously, and is filtered in the kidney. Given as a hypertonic solution, it increases distal tubule delivery of Na+ and water, resulting in increased urine formation.
Mannitol can also be used to open the blood-brain barrier by temporarily shrinking the tightly coupled endothelial cells that make up the barrier. This makes mannitol indispensable for delivering various drugs directly to the brain (e.g. in the treatment of Alzheimer's disease).
Mannitol is also used as a sweetener for people with diabetes. Since mannitol has a negative heat of solution, it is used as a sweetener in "breath-freshening" candies, the cooling effect adding to the fresh feel. In doses larger than 20g, mannitol acts as a laxative, and is sometimes sold as a laxative for children.
It is sometimes used as an adulterant for heroin, methamphetamines or other illicit drugs.
Mannitol can also be used to temporarily encapsulate a sharp object (such as a helix on a lead for an artificial pacemaker) while it is passing through the venous system. Because it dissolves readily in blood, the sharp point will become exposed by the time it reaches its destination.
Mannitol may be admininstered in cases of severe Ciguatera poisoning. Severe ciguatoxin, or "tropical fish poisoning" can produce stroke-like symptoms.
Mannitol is a non-permeating molecule i.e. it cannot cross biological membranes.
External links
"Mannitol"