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It can be used to lower intraocular pressure and in the postoperational period in ophthalomological procedures as well as during brain edema.

D-mannitol (D-mannohexan-1.2.3.4.5.6-hexaol) is a constituent of several plants including the Manna ash, several edible plants, and seaweed. Parts of the latter contain up to 10 % mannitol by weight. The solubility in water is approximately 230 g/L at room temperature and it increases with increasing temperature. Mannitol is stable under the common processing conditions of foods.
Mannitol is approximately 50 % as sweet as sucrose and non-cariogenic. In the European Union, maltitol is approved as E 421 for a large number of food applications. In the United States, mannitol produced by hydrogenation of glucose or fructose solutions or by fermentation by Zygosaccharomyces rouxii or Lactobacillus intermedius is approved for several food applications. It is also approved in many other countries.

A soluble hexahydric alcohol that occurs in many plants and fungi. It is used in medicines and as a sweetener (particularly in foods for diabetics). It is an isomer of sorbitol.

mannitol: A polyhydric alcohol,CH₂OH(CHOH)₄CH₂OH, derived frommannose or fructose. It is the mainsoluble sugar in fungi and an importantcarbohydrate reserve in brownalgae. Mannitol is used as a sweetenerin certain foodstuffs and as a diureticto relieve fluid retention.

There are two main processes for industrial production of mannitol in the world. One is to take kelp as raw material. While producing alginate, the soaking solution of kelp after iodine extraction is obtained through multiple concentration, impurity removal, separation, evaporation concentration, cooling and crystallization; One is obtained from sucrose and glucose by hydrolysis, differential isomerization and enzyme isomerization, and then hydrogenation. China has used kelp to extract mannitol for decades. This process is simple and easy, but its development has been restricted for a long time due to the limitations of raw material resources, extraction yield, climatic conditions and energy consumption. The annual output of mannitol in China in the last century has never exceeded 8000 tons. The synthetic process in China began to be tested in the 1980s and came out in the 1990s. However, it has made great progress because it is not limited by raw materials and suitable for large-scale production.

The by far largest quantity of mannitol is produced by chemical hydrogenation of fructose which yields a mixture of mannitol and sorbitol. The mixture is subjected to fractionated crystallization. As direct sorbitol production is less costly, the processing costs have mostly to be borne by mannitol which makes it more expensive than sorbitol. Production from seaweed seems to be of limited importance.
Possibilities to produce mannitol by fermentation were studied using several organisms. They mostly use fructose as an acceptor for hydrogen and glucose as a source of carbon. In a fed-batch culture of C. magnoliae with 50 g/L of glucose as the initial carbon source and increasing levels of fructose up to 300 g/L in 120 h, 248 g/L of mannitol were obtained from 300 g/L of fructose equivalent to a conversion rate of 83 % and a productivity of 2.07 g/Lh. High yields were obtained from Lactobacillus fermentum grown in a batch reactor. The conversion rates increased from 25 to 35 C to 93.6 % with average and high productivities of 7.6 and 16.0 g/Lh. A fast mannitol production of 104 g/L within 16 h was obtained from L. intermedius on molasses and fructose syrups in a concentration of 150 g/L with a fructose-to-glucose rate of 4:1. High productivity (26.2 g/Lh) and conversion rates (97 mol%) were obtained in a high cell density membrane cell recycle bioreactor. Increase of the fructose concentration above 100 g/L reduced the productivity. A fed-batch process with L. intermedius yielded 176 g/L of mannitol from 184 g/L fructose and 94 g/L glucose within 30 h. The productivity of 5.6 g/Lh could be increased to more than 40 g/Lh at the expense of reduced mannitol yield and increased residual substrate concentrations.
As mannitol is more expensive than sorbitol, production by fermentation may become an alternative to hydrogenation of fructose.

Mannitol is a good diuretic in medicine. It can reduce intracranial pressure, intraocular pressure, kidney medicine, dehydrating medicine, sugar substitute, excipient of tablets and diluent of solid and liquid. As a hypertonic antihypertensive drug, Injectio mannitou injection is commonly used in clinical rescue, especially in the rescue of brain diseases. It has the characteristics of fast antihypertensive and accurate curative effect required by drugs to reduce intracranial pressure. After mannitol enters the body, it can increase the plasma osmotic pressure, dehydrate the tissue, and reduce the intracranial pressure and intraocular pressure. After glomerular filtration, it is not easy to be reabsorbed by renal tubules, increase the urinary osmotic pressure, bring out a large amount of water and dehydrate. It is used for edema caused by craniocerebral trauma, brain tumor and brain tissue hypoxia, edema caused by large-area burn, ascites and glaucoma caused by renal failure. It can prevent and treat early acute renal insufficiency.

Today, mannitol is the most widely used osmotic diuretic. It raises osmotic pressure in renal tubules, thus reducing reabsorption of water in the nephrons. As a result, a large quantity of free water is released, sodium secretion increases, and as a rule, an insignificant amount of potassium is secreted. Mannitol is used as an adjuvant drug for preventing oliguria and anuriua.

Mannitol is the agent most commonly used as an osmotic diuretic. Sorbitol also can be used for similar reasons.Mannitol is administered intravenously in solutions of 5 to 50% at a rate of administration that is adjusted to maintain the urinary output at 30 to 50 ml/hour. Mannitol is filtered at the glomerulus and is poorly reabsorbed by the kidney tubule. The osmotic effect of mannitol in the tubule inhibits the reabsorption of water, and the rate of urine flow can be maintained. It also is used to reduce intracranial pressure by reducing cerebral intravascular volume.

Mannitol is used to promote diuresis in acute oliguric renal failure, reduce intraocular and intracerebral pressures, enhance urinary excretion of some toxins, (e.g., aspirin, some barbiturates, bromides, ethylene glycol) and, in conjunction with other diuretics, to rapidly reduce edema or ascites when appropriate (see Contraindications- Precautions below). In humans, it is also used as an irrigating solution during transurethral prostatic resections.