Pharmacology · Class
Osmotic diuretics !
Sugars given into a vein that are filtered but not reabsorbed: they hold water in the tubule and draw water out of the brain and the eye.
Updated 2026-11-01
What they are
Small, inert molecules (mainly mannitol) that are freely filtered by the glomerulus and barely reabsorbed. Today they are used mainly to lower raised intracranial pressure and raised intraocular pressure.
Mechanism of action
In the blood they raise osmolality and pull water out of cells, including brain and eye tissue. In the tubule the unabsorbed molecules hold water in the lumen, so water and, to a lesser degree, sodium are lost in the urine.
Target: No receptor: osmotic effect in plasma and tubular fluid
Drugs in this class
Others in the class
- Urea
- Glycerol
Test yourself
Think of the answer, then tap the question to see it.
How does mannitol lower intracranial pressure?
It raises plasma osmolality and draws water out of brain tissue into the blood, which shrinks brain volume.
Why can mannitol worsen heart failure?
Before the diuresis it pulls water from cells into the bloodstream, expanding plasma volume and loading the heart, which can cause pulmonary oedema.
Can you name two contraindications of mannitol?
Anuria and severe hypovolaemia; also active intracranial bleeding outside a craniotomy.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - MANNITOL injection, solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.