Mannitol is an osmotic diuretic, meaning it works by drawing water out of cells and into the bloodstream. This increases the volume of blood plasma and decreases the concentration of sodium in the blood [1]. The increased plasma volume stimulates diuresis, which is the increased production of urine [1].
How does mannitol affect the body?
Mannitol acts by increasing the osmotic pressure in the renal tubules. As it is filtered by the glomerulus and not reabsorbed in the proximal tubule or loop of Henle, it remains in the tubular fluid. This presence of mannitol inhibits water and sodium reabsorption, leading to increased urine output [2]. This process can help reduce intracranial pressure by drawing excess fluid from the brain tissue into the blood [3]. It also reduces intraocular pressure by decreasing the volume of aqueous humor in the eye [4].
Why is mannitol used in medicine?
Mannitol is primarily used to reduce swelling and pressure in the brain and eyes. It is administered intravenously to treat conditions such as cerebral edema, which can occur after head injuries or brain surgery [3]. It is also used to manage elevated intraocular pressure in certain eye conditions [4]. In some cases, it can be used to promote urinary excretion of toxic substances [2].
What are the risks or side effects of mannitol?
Potential side effects of mannitol include electrolyte imbalances, such as hyponatremia (low sodium levels) or hyperkalemia (high potassium levels) [1]. It can also lead to dehydration, headache, nausea, and dizziness [1]. In rare instances, it may cause allergic reactions or kidney damage [2]. Patients with heart failure or significant kidney impairment may be at higher risk for adverse effects [1].
How is mannitol administered and dosed?
Mannitol is typically administered intravenously as an infusion [3]. The dosage and rate of administration depend on the patient's condition and response. For reducing intracranial pressure, doses usually range from 0.25 to 1 gram per kilogram of body weight, infused over a period of 30 to 60 minutes [3]. For lowering intraocular pressure, doses may be similar but administered over a longer timeframe to allow for gradual effect [4].
What is the difference between mannitol and other diuretics?
Unlike other diuretics that act by inhibiting specific ion transporters in the kidney, mannitol is an osmotic diuretic. Its diuretic effect is due to its osmotic properties, drawing water into the urine without directly interfering with electrolyte transport mechanisms in the same way as loop diuretics or thiazides [2]. This distinction makes it useful for specific conditions, particularly when rapid reduction of fluid volume is needed to alleviate pressure in confined spaces like the skull [3].