Mannitol is an isomer of sorbitol. It is produced by hydrogenation of fructose.
Mannitol is a white, odourless substance, available in either granular or powder form. Mannitol has a subtle taste, distinctively pleasant, slightly sweet, and cool. It has a smooth mouth-feel that is not gritty. The sweetness is about half that of sucrose.
Mannitol neither adds moisture nor contributes to moisture pick-up, thereby eliminating a common cause of degradation of therapeutic actives. Mannitol is not self- degradable, nor does it degrade actives which might react with sugars.
Mannitol has almost no flavour of its own, but does impart a unique sensation of smooth, cool mouth-feel. 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.
Mannitol is like sorbitol used as a sweetener for people with diabetes.
Its sweetness and coolness combine ideally with flavouring agents to help mask undesirable medicinal tastes and build up a good flavour system. The inertness of mannitol and its freedom from moisture make it a desirable base in conventional tablets containing moisture, sensitive drugs or ingredients that might react with other tablet bases. These properties have also given it acceptance as a diluent for many sensitive drugs and vitamins.
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).