Osmotic diuretics (also: osmodiuretics , osmotics ) are high-molecular substances , i.e. those with a high molecular mass that are freely filtered in the glomerulus of the kidney , but cannot be reabsorbed in the further course of the renal tubule . As a result, they osmotically retain water in the urine , which would normally have been reabsorbed from the primary urine.
Another example of an osmotic diuretic is glucose (grape sugar). In people with diabetes , when the blood sugar level reaches a certain level, glucose crosses over into the urine when the filtration capacity of the kidney tubules is exhausted. This triggers an increased flow of urine, as sugar binds water osmotically. This fact gave the diabetes its name: Diabetes mellitus means in German "honey-sweet flow".
Mannitol is used, for example, to treat brain edema . Here, a hypertonic solution of the active ingredient is infused intravenously so that the excess water can flow off following the osmotic pressure and consequently the intracranial pressure in the affected area drops.