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Mannitol (E421) – Uses, Effects and Dosage

Mannitol is a natural sugar alcohol used as a sweetener, pharmaceutical excipient, and osmotic diuretic in clinical medicine.

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Things worth knowing about "Mannitol"

Mannitol is a natural sugar alcohol used as a sweetener, pharmaceutical excipient, and osmotic diuretic in clinical medicine.

What is Mannitol?

Mannitol (also known as Mannit or food additive E421) is a six-carbon sugar alcohol that occurs naturally in many plants, fungi, and algae. Chemically, it is derived from mannose and belongs to the group of polyols. Natural sources include ash trees, seaweed, mushrooms, and various fruits. It is produced industrially by the hydrogenation of mannose or fructose.

Areas of Application

As a Food Additive

In the food industry, mannitol is used as a sweetener (E421). It has approximately 50–70% of the sweetness of table sugar (sucrose) and is commonly found in sugar-free chewing gums, confectionery, and dietary supplements. Because mannitol is only slowly and incompletely absorbed in the small intestine, it has a low glycaemic index and is suitable as a sugar substitute for people with diabetes.

As a Pharmaceutical Agent

In medicine, mannitol is primarily used as an osmotic diuretic. It is administered intravenously and increases the osmotic pressure in the blood and renal tubules, thereby promoting the excretion of water and electrolytes through the kidneys. Key medical indications include:

Cerebral oedema: Mannitol reduces intracranial pressure by drawing fluid from brain tissue into the bloodstream.
Acute kidney injury: To promote urine production and prevent tubular damage.
Poisoning: To increase renal elimination of toxic substances.
Glaucoma: For short-term reduction of intraocular pressure.

As a Pharmaceutical Excipient

Mannitol serves as a filler and carrier in tablets, capsules, and lyophilised (freeze-dried) medications due to its chemical stability, non-hygroscopic nature, and good tolerability.

Mechanism of Action

As an osmotically active substance, mannitol is freely distributed in the blood plasma after intravenous administration but is neither metabolised nor significantly reabsorbed in the renal tubules. Mannitol remains in the tubular filtrate and osmotically retains water, significantly increasing urine output (diuresis). At the same time, mannitol raises plasma osmolality, causing tissue fluid -- for example from the brain -- to be drawn back into the vascular compartment.

Dosage and Administration

The dosage of mannitol as a pharmaceutical agent depends on body weight and the clinical indication. Typical intravenous doses range from 0.25 to 2 g per kilogram of body weight, administered as an infusion over 30–60 minutes. Its use is restricted to clinical settings under medical supervision.

Side Effects and Risks

When used as directed, mannitol is generally well tolerated. Possible side effects include:

Electrolyte imbalances (e.g., hyponatraemia, hypokalaemia)
Dehydration due to excessive diuresis
Headache, dizziness, and nausea
Cardiovascular strain from increased blood volume
Renal damage possible at high doses

When consumed orally in large amounts as a food additive, mannitol can have a laxative effect and cause bloating and diarrhoea, as it is fermented by bacteria in the large intestine.

Contraindications

Mannitol should not be used or should be used with caution in patients with:

Severe renal insufficiency (anuria)
Severe heart failure
Pulmonary oedema
Intracranial haemorrhage (except in life-saving procedures)
Severe dehydration

References

European Medicines Agency (EMA): Summary of Product Characteristics -- Mannitol 20% Solution for Infusion, 2023.
Brunton, L. L.; Hilal-Dandan, R.; Knollmann, B. C.: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th Edition, McGraw-Hill, 2018.
European Food Safety Authority (EFSA): Re-evaluation of mannitol (E 421) as a food additive. EFSA Journal, 2019.

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