Sorbitol osmotic diuretic

Manufacture of vitamin C starts with the conversion of sorbitol to L-sorbose. Sorbitol and xyHtol have been used for parenteral nutrition following severe injury, bums, or surgery (246). An iron—sorbitol—citric acid complex is an intramuscular bematinic (247). Mannitol administered intravenously (248) and isosorbide administered orally (249) are osmotic diuretics. Mannitol hexanitrate and isosorbide dinitrate are antianginal dmgs (see Cardiovascular agents). 

These include mannitol and sorbitol which act mainly in the proximal tubules to prevent reabsorption of water. These polyhydric alcohols cannot be absorbed and therefore bind a corresponding volume of water. Since body cells lack transport mechanisms for these substances (structure on p.175), they also cannot be absorbed through the intestinal epithelium and thus need to be given by intravenous infusion. The result of osmotic diuresis is a large volume of dilute urine, as in decompensated diabetes melli-tus. Osmotic diuretics are indicated in the prophylaxis of renal hypovolemic failure, the mobilization of brain edema, and the treatment of acute glaucoma attacks (p. 346). 

Among the plant derived diuretics, the xanthine derivatives have this mode of action, whereas the osmotic diuretics, mannitol and sorbitol, which produce a glomerular filtration, but not resorption in the tubules, incease the excretion of water. 

Polyols, such as mannitol, sorbitol, and isosorbide, provide this effect. Sugars, such as glucose and sucrose, also can have a diuretic effect by this mechanism. Although not a polyol, urea has a similar osmotic effect and has been used in the past as an osmotic diuretic. 

Mannitol is the agent most commonly used as an osmotic diuretic. Sorbitol also can be used for similar reasons. These compounds can be prepared by the electrolytic reduction of glucose or sucrose. 

On the other hand, borohydride reduction of the ketose o-fructose will give a mixture of o-glucitol and its epimer, D-mannitol. A better approach to D-mannitol would be reduction of the aldose D-mannose. o-Glucitol (sorbitol) is found naturally in the ripe berries of the mountain ash (Sorbus aucuparia), but is prepared semi-synthetically from glucose. It is half as sweet as sucrose, is not absorbed orally, and is not readily metabolized in the body. It finds particular use as a sweetener for diabetic products. o-Mannitol also occurs naturally in manna, the exudate of the manna ash Fraxinus ornus. This material has similar characteristics to sorbitol, but is used principally as a diuretic. It is injected intravenously, is eliminated rapidly into the urine, and removes fluid by an osmotic effect. 

Besides the use as filling agents and laxatives the hexoles are used as humectants (e.g. sorbitol in creams), for taste correction (e.g. sorbitol in oral liquids), to get iso-osmotic solutions (e.g., mannitol in eyewashes, see Sect. 10.6.2), as diuretics in parenterals and as a cake stabilising agent in freeze drying. 

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