Mannitol
Mannitol is a potent **osmotic diuretic** primarily utilized in emergency and critical care veterinary medicine. It is a sugar alcohol that draws fluid from the intracellular to the extracellular space. **Key Indications:** * Management of **acute oliguric renal failure** (to promote diuresis) * Reduction of **intracranial pressure (ICP)** and cerebral edema (e.g., traumatic brain injury) * Reduction of **intraocular pressure (IOP)** in acute glaucoma * Enhancement of urinary excretion of specific toxins (e.g., aspirin, barbiturates, bromides, ethylene glycol) > **Clinical Pearl:** Because mannitol causes rapid fluid shifts, it is highly effective but requires strict monitoring of the patient's volume and hydration status. It must be administered with an in-line filter due to its tendency to crystallize at room temperature.
Mechanism: Mannitol is freely filtered at the glomerulus and poorly reabsorbed in the renal tubules. * **Osmotic Diuresis:** The presence of mannitol in the tubular fluid increases osmotic pressure โ prevents water reabsorption โ proportionately increases water excretion along with sodium, uric acid, and urea. * **Neuroprotection & ICP Reduction:** Increases intravascular osmolarity โ draws water from brain parenchyma across an intact blood-brain barrier (BBB) into the intravascular space โ decreases cerebral edema and CSF pressure. * **Renal Protection:** Dilates renal arterioles โ decreases vascular resistance and blood viscosity โ increases renal blood flow and glomerular filtration rate (GFR). It also minimizes renal tubular swelling and prevents the concentration of nephrotoxins in tubular fluid.
Dosing by species
- Cerebral edema ยท 1-3 gram/kg IV ยท IV ยท Single dose ยท Usually given with steroids and/or DMSO.
- Oliguric renal failure ยท 1-2 gram/kg (5-10mL of 20% solution) IV ยท IV ยท Single dose ยท Give after rehydration; monitor urine flow and fluid balance.
- Cerebral edema ยท 1-3 gram/kg IV ยท IV ยท Single dose ยท Usually given with steroids and/or DMSO.
- Oliguric renal failure ยท 1-2 gram/kg (5-10mL of 20% solution) IV ยท IV ยท Single dose ยท Give after rehydration; monitor urine flow and fluid balance.
- Oliguric renal failure (not anuric) ยท 0.25-0.5 gram/kg IV over 5-10 minutes ยท IV ยท May repeat q4-6 hours or as CRI for first 12-24 hours ยท 12-24 hours ยท After correcting fluid, electrolyte, acid/base balance. CRI dose is 8-10% solution.
- Oliguric renal failure (rehydrated, not fluid overloaded) ยท 0.25-0.5 gram/kg IV slowly over 5-10 minutes; repeat dose at 30-40 minute intervals up to 1.5 gram/kg total ยท IV ยท q30-40min ยท Up to 1.5 g/kg total
- Oliguric renal failure (fluid replete) ยท 0.5 gram/kg IV over 20-30 minutes; if significant diuresis is accomplished within 30 minutes, may administer as a CRI of 60-120 mg/kg/hr IV or as intermittent boluses repeated every 4-6 hours ยท IV ยท CRI or q4-6h ยท Contraindicated in patients who are dehydrated, hypervolemic, or anuric.
- Acute glaucoma ยท 0.5-1 gram/kg IV given over 15-20 minutes ยท IV ยท Single dose ยท Withhold water for 3-4 hours. IOP reduction begins in 20-30 mins.
Routes of administration
Contraindications
- Anuria secondary to renal disease
- Severe dehydration
- Severe pulmonary congestion or pulmonary edema
- Intracranial bleeding (unless during craniotomy - human label)
- Disrupted capillary membrane in the brain (can leak into interstitium and worsen edema)
- Severe pulmonary congestion
- Pulmonary oedema
- Intracranial haemorrhage (relative contraindication; labelled 'use with care' but commonly used in traumatic brain injury)
Adverse effects
- Fluid and electrolyte imbalances (especially hypernatremia)
- Volume overload (if oliguria persists)
- Nausea and vomiting
- Pulmonary edema
- Congestive heart failure (CHF)
- Tachycardia
- Dizziness and headache (CNS effects)
- Fluid and electrolyte imbalances
- Circulatory overload (at high doses)
- Acidosis (at high doses)
- Thrombophlebitis
- Extravasation injury (oedema and skin necrosis)
- Diarrhoea (if administered orally)
- Acute renal failure (rare)
Drug interactions
- Lithium ยท Mannitol can increase the renal elimination of lithium
- Sotalol ยท Mannitol's effects on potassium and magnesium may increase the risk for QT prolongation
- Potassium-depleting diuretics ยท May exacerbate diuretic-induced hypokalaemia ยท moderate
- Beta-blockers ยท Concurrent use with potassium-depleting diuretics requires caution ยท moderate
- Ciclosporin ยท Nephrotoxicity has been described with concurrent use in humans ยท major
- Whole blood ยท Mannitol should never be added to whole blood for transfusion or given through the same IV set ยท major
- KCl or NaCl ยท Do not add to concentrated mannitol solutions (20% or 25%) as a precipitate may form ยท major
Monitoring
- Serum electrolytes (especially sodium)
- Serum osmolality
- BUN and serum creatinine
- Urine output
- Central venous pressure (CVP), if possible
- Lung auscultation (to monitor for pulmonary edema)
- Intracranial pressure (ICP) or neurological status
- Intraocular pressure (IOP)
- Hydration status and body weight
- Serum electrolytes (especially potassium and sodium)
- Renal function (BUN, creatinine)
- Acid-base balance
Overdose
Inadvertent overdosage can cause excessive excretion of sodium, potassium, and chloride. If urine output is inadequate, **water intoxication** or **pulmonary edema** may occur. **Treatment:** * Halt mannitol administration immediately. * Monitor and correct electrolyte and fluid imbalances. * Hemodialysis is effective in clearing mannitol from the bloodstream.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.