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Acute Oliguric Renal Failure / Raised ICP Pregnancy: UK SPC §4.6, verbatim: 'There are no adequate published data from the use of mannitol in pregnant women. There are no adequate published data, from animal studies, with respect to mannitol's effect on pregnancy and/or embryo/foetal development and/or parturition and/or postnatal development. Mannitol should not be used during pregnancy unless clearly needed. There is no information on excretion of mannitol in breast milk. Mannitol should not be used during lactation unless clearly necessary.' The US label §8.1 is less restrictive: 'The available case report data with mannitol over decades of use have not identified a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. Mannitol crosses the placenta and may cause fluid shifts that could potentially result in adverse effects in the fetus... Published literature reports the presence of mannitol in amniotic fluid when mannitol is administered to pregnant women during the third trimester of pregnancy.' For UK use the SPC wording governs.

Mannitol (Osmotic Diuretic — Renal/Neurological)

Brand names: Osmofundin 15%, Mannitol 20%

Mannitol is an intravenous osmotic diuretic used to reduce raised intracranial or intraocular pressure and, less commonly, to promote diuresis. This entry covers its use in renal and neurological settings.

Adult dose

Dose: Acute renal failure (UK SPC §4.2) — general dose range 50 to 200 g mannitol in a 24 hour period; in most instances an adequate response is achieved at 50 to 100 g mannitol/day. In marked oliguria or suspected inadequate renal function a TEST DOSE MUST COME FIRST: approximately 200 mg mannitol/kg body weight over 3 to 5 minutes (for a 70 kg adult, approximately 75 mL of a 20% solution or 100 mL of a 15% solution), with mannitol continued only if an adequate urine flow follows.
Route: Intravenous infusion. UK SPC §4.2: 'This hypertonic solution should be administered via a large peripheral or preferably a central vein. Rapid infusion in peripheral veins may be harmful.' Use an administration set with a final in-line filter 'because of the potential for mannitol crystals to form'. US §2.1: 'preferably into a large central vein.'
Frequency: Rate is titrated to urine output, not given as a fixed interval. UK SPC §4.2: 'The rate of administration is usually adjusted to maintain a urine flow of at least 30-50 ml/hour. Only in emergency situations, the maximum infusion rate can be as high as 200 mg/kg infused over 5 minutes (see also test dose). After 5 minutes, the infusion rate should be readjusted to maintain a urine flow of at least 30-50 ml/hour, with a maximal dose of 200 g/24h.'
Max: Maximum 200 g mannitol in any 24 hour period, with a dosage limit of 50 g on any one occasion (UK SPC §4.2, acute renal failure).
SCOPE: this covers the page's primary indication — acute renal failure / oliguria (the page sits in the renal specialty and its category leads with 'Acute Oliguric Renal Failure'). The page also lists raised ICP and perioperative AKI prevention. Raised ICP IS sourced in this bundle and is drafted on the mannitol_20 record (UK SPC 1.5 to 2 g/kg over 30 to 60 minutes; US OSMITROL 0.25 g/kg over 30 minutes every 6 to 8 hours — the two labels disagree). PERIOPERATIVE AKI PREVENTION IS NOT SOURCED ANYWHERE IN THIS BUNDLE. || VERBATIM UK SPC §4.2, Acute renal failure: 'The general dose range is 50 to 200 g mannitol (500 ml to 2000 ml/day) in a 24 hour period, with a dosage limit of 50 g (500ml mannitol) on any one occasion. In most instances, adequate response will be achieved at a dosage of 50 to 100 g mannitol/day (500 ml to 1000 ml /day). The rate of administration is usually adjusted to maintain a urine flow of at least 30-50 ml/hour.' || ⚠️ STRENGTH TRAP: the SPC in this bundle is for MANNITOL 10%, so every bracketed millilitre figure above (500 mL = 50 g, 2000 mL/day = 200 g) is a 10% VOLUME. This page's brands are Osmofundin 15% and Mannitol 20%, in which the same gram dose occupies two-thirds or half that volume. Only the gram figures are published above. The SPC's own test-dose example does give the volumes for this page's strengths, verbatim: 'in an adult patient with a body weight of 70 kg: approximately 75 ml of a 20% solution or 100 ml of a 15% solution.' US §3 confirms '20% (0.2 grams/mL): 20 grams of mannitol, USP per 100 mL'. || VERBATIM UK SPC §4.2, test dose in oliguria/renal impairment: 'Patients with marked oliguria or suspected inadequate renal function should first receive a test dose of approximately 200 mg mannitol/kg bw (2ml/kg bw) over a period of 3 to 5 minutes... The response to the test dose is considered adequate if at least 30-50 ml/hour of urine is excreted for 2-3 hours. If an adequate response is not attained, a further test dose may be given. If an adequate response to the second test dose is not attained, treatment with mannitol should be discontinued and the patient reassessed as established renal failure may be present.' || ALSO IN THE BUNDLE, forced diuresis in poisoning (UK SPC §4.2, verbatim): 'In forced diuresis, the dose of mannitol should be adjusted to maintain urinary output of at least 100ml/hour and positive fluid balance of 1-2 litres. An initial loading dose of approximately 25 g (250 ml) may be given.' || ELDERLY (UK SPC §4.2, verbatim): 'The general dose range is the same as for adults, 50 to 200 g in a 24 hour period (500 ml to 2000ml/day), with a dosage limit of 50 g mannitol (500 ml) on any one occasion. Since incipient renal insufficiency may be present, caution should be used when reviewing patient's status prior to dose selection.' || CRYSTALLISATION: UK SPC — re-dissolve by warming to 37°C with gentle agitation, dry heat only, never water or a microwave; the US label instead says 70°C. Follow the SPC in the UK.

Paediatric dose

Dose: 0.5 g/kg
Route: Intravenous infusion through an administration set with a final in-line filter
Frequency: UK SPC §4.2 (paediatric population): 'This dose may be repeated once or twice, after an interval of 4 to 8 hours, if necessary.'
Max: No maximum paediatric dose is stated in either label.
VERBATIM UK SPC §4.2, Paediatric population: 'In renal insufficiency, the test dose should be 200 mg mannitol/kg bw (2 ml/kg bw) over 3-5 minutes. The treatment dose ranges from 0.5 to 1.5 g/kg bw (5 ml/kg bw to 15 ml/kg bw). This dose may be repeated once or twice, after an interval of 4 to 8 hours, if necessary. For cerebral and ocular oedema, this dose may be given over 30 to 60 minutes as for adults.' The per-kg figure above is for the TREATMENT dose; note the separate 200 mg/kg TEST dose that must precede it in renal insufficiency. dosePerKg is set to the LOWER bound of the sourced range; the full sourced per-dose range is 0.5 to 1.5 g/kg. || ⚠️ concentration is deliberately left NULL. The SPC's bracketed '5 ml/kg bw to 15 ml/kg bw' is for the 10% solution it describes, whereas this page carries two different brand strengths (Osmofundin 15% and Mannitol 20%), so there is no single strength the calculator could safely assume. Work the volume out from the actual bag. || US §8.4 Pediatric Use, verbatim: 'Studies have not defined the optimal dose of OSMITROL in the pediatric population... pediatric patients less than two years of age, particularly preterm and term neonates, may be at higher risk for fluid and electrolyte abnormalities following OSMITROL administration due to decreased glomerular filtration rate and limited ability to concentrate urine.' Verify against a children's formulary and local paediatric nephrology/critical-care protocol.

Dose adjustments

Renal

This IS the page's indication, and the labels manage it with a test dose and a stop rule rather than a numeric reduction. UK SPC §4.2, verbatim: 'Patients with marked oliguria or suspected inadequate renal function should first receive a test dose of approximately 200 mg mannitol/kg bw (2ml/kg bw) over a period of 3 to 5 minutes. For example: in an adult patient with a body weight of 70 kg: approximately 75 ml of a 20% solution or 100 ml of a 15% solution. The response to the test dose is considered adequate if at least 30-50 ml/hour of urine is excreted for 2-3 hours. If an adequate response is not attained, a further test dose may be given. If an adequate response to the second test dose is not attained, treatment with mannitol should be discontinued and the patient reassessed as established renal failure may be present.' UK SPC §4.4, verbatim: 'Mannitol should be administered with caution to patients with severely impaired renal function. A test dose should be employed and therapy with mannitol continued only if an adequate urine flow is achieved (see section 4.2). If the urine output declines during mannitol infusion, the patient's clinical status should be closely reviewed'; and 'Reversible, acute oligoanuric renal failure has occurred in patients with normal pre-treatment renal function, who received large intravenous doses of mannitol. Progressive renal damage or dysfunction, after institution of mannitol therapy, including increasing oliguria and azotemia, has also been described... osmotic nephrosis in general is known to potentially proceed to chronic or even end-stage renal failure. Patients with pre-existing renal disease, or those receiving potentially nephrotoxic drugs, are at increased risk of renal failure following administration of mannitol.' Well established anuria is an absolute contraindication (§4.3). Some sections of the product information we used were incomplete — check the full SPC.

Hepatic

Not stated — neither label in this bundle contains a hepatic-impairment dosing statement.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

VERBATIM UK SPC §4.2, Paediatric population: 'In renal insufficiency, the test dose should be 200 mg mannitol/kg bw (2 ml/kg bw) over 3-5 minutes. The treatment dose ranges from 0.5 to 1.5 g/kg bw (5 ml/kg bw to 15 ml/kg bw). This dose may be repeated once or twice, after an interval of 4 to 8 hours, if necessary. For cerebral and ocular oedema, this dose may be given over 30 to 60 minutes as for adults.' The per-kg figure above is for the TREATMENT dose; note the separate 200 mg/kg TEST dose that must precede it in renal insufficiency. dosePerKg is set to the LOWER bound of the sourced range; the full sourced per-dose range is 0.5 to 1.5 g/kg. || ⚠️ concentration is deliberately left NULL. The SPC's bracketed '5 ml/kg bw to 15 ml/kg bw' is for the 10% solution it describes, whereas this page carries two different brand strengths (Osmofundin 15% and Mannitol 20%), so there is no single strength the calculator could safely assume. Work the volume out from the actual bag. || US §8.4 Pediatric Use, verbatim: 'Studies have not defined the optimal dose of OSMITROL in the pediatric population... pediatric patients less than two years of age, particularly preterm and term neonates, may be at higher risk for fluid and electrolyte abnormalities following OSMITROL administration due to decreased glomerular filtration rate and limited ability to concentrate urine.' Verify against a children's formulary and local paediatric nephrology/critical-care protocol.

Verify in a children's formulary

Contraindications

  • Pre-existing plasma hyperosmolarity (UK SPC §4.3)
  • Severe dehydration (UK SPC §4.3)
  • Well established anuria (UK SPC §4.3; the US label §4 gives this as 'Anuria')
  • Severe heart failure (UK SPC §4.3)
  • Severe pulmonary congestion or pulmonary oedema (UK SPC §4.3; US §4: 'Pre-existing severe pulmonary vascular congestion or pulmonary edema')
  • Active intracranial bleeding, except during craniotomy (UK SPC §4.3 and US §4)
  • Disturbance of the blood-brain barrier (UK SPC §4.3)
  • Hypersensitivity to mannitol (UK SPC §4.3 and US §4)
  • Severe hypovolaemia — listed in the US label §4 only; it does not appear in the UK SPC §4.3 list

Side effects

  • Hypersensitivity — allergic reaction and anaphylactic reaction including anaphylactic shock, with skin, gastrointestinal, severe circulatory (hypotension) and respiratory (e.g. dyspnoea) manifestations; the US label also lists cardiac arrest. UK SPC §4.4: 'Fatal outcome has been reported.' Frequency 'Not known'
  • Other hypersensitivity / infusion reactions: hypertension, pyrexia, chills, sweating, cough, musculoskeletal stiffness and myalgia, urticaria/rash, pruritus, generalised pain, discomfort, nausea, vomiting, headache (UK SPC §4.8)
  • Fluid and electrolyte imbalance: hypervolaemia, peripheral oedema, dehydration, hyponatraemia, hypernatraemia, hyperkalaemia, hypokalaemia; metabolic acidosis (UK SPC §4.8). The US label adds hypovolaemia
  • CNS toxicity: convulsions, coma, confusion, lethargy — UK SPC §4.4: 'CNS toxicity manifested by, e.g. confusion, lethargy, and coma has been reported in patients treated with mannitol, in particular in the presence of impaired renal function. Fatal outcomes have been reported.'
  • Rebound intracranial pressure increase — UK SPC §4.4: 'A rebound increase of intracranial pressure may occur several hours after the use of mannitol. Patients with compromised blood brain barrier are at increased risk.'
  • Headache, dizziness, blurred vision (UK SPC §4.8)
  • Renal and urinary: excessive diuresis, osmotic nephrosis, urinary retention, acute renal failure, azotaemia, anuria, oliguria, polyuria (UK SPC §4.8); the US label adds acute kidney injury and haematuria
  • Cardiac and respiratory: cardiac arrhythmia, congestive heart failure, pulmonary oedema, rhinitis (UK SPC §4.8)
  • Gastrointestinal: dry mouth, thirst, nausea, vomiting (UK SPC §4.8)
  • Skin: skin necrosis, urticaria; musculoskeletal cramps (UK SPC §4.8)
  • Infusion site reactions: infusion thrombophlebitis, inflammation, pain, rash, erythema, pruritus; compartment syndrome associated with extravasation and swelling at the injection site (UK SPC §4.8)
  • General: chills, angina-like chest pain, fever, asthenia, malaise (UK SPC §4.8)
  • All UK SPC §4.8 reactions are post-marketing with frequency 'Not known'; the section states the frequency 'cannot be estimated from the available data'

Monitoring

  • Before administration (US §2.1 / §2.2, verbatim): 'evaluate renal, cardiac and pulmonary status of the patient and correct fluid and electrolyte imbalances.'
  • UK SPC §4.4, verbatim: 'Serum osmolar gap and renal function should be closely monitored and appropriate action initiated, should signs of worsening renal function appear.'
  • US §2.2, verbatim: 'During and following OSMITROL infusion, monitor fluid and electrolytes, serum osmolarity, and renal, cardiac and pulmonary function. Discontinue OSMITROL if renal, cardiac, or pulmonary status worsens or CNS toxicity develops.'
  • US §5.5 highlight, verbatim: 'Monitoring/Laboratory Tests : Monitor fluid and electrolytes, serum osmolarity and renal, cardiac and pulmonary function. Discontinue if toxicity develops.'
  • Urine output — the UK SPC titrates the infusion rate 'to maintain a urine flow of at least 30-50 ml/hour' (§4.2, acute renal failure and test-dose sections).
  • US §5.7: 'Interference with Laboratory Tests : High concentrations of mannitol may cause false low results of inorganic' [the sentence is cut at the bundle's source-fetch limit] — treat laboratory phosphate/inorganic results with caution during mannitol infusion and verify against the full label.
  • NOTE: no target serum osmolality figure appears anywhere in the fetched bundle; it is NOT sourced here.
  • US §7 drug interactions bearing on renal use, verbatim: 'Nephrotoxic Drugs and Diuretics : May increase the risk of renal failure; avoid concomitant use'; 'Concomitant administration of nephrotoxic drugs (e.g., cyclosporine, aminoglycosides) increases the risk of renal failure following administration of mannitol'; 'Renally Eliminated Agents : Concomitant use may decrease the effectiveness of agents that undergo significant renal elimination. However, concomitant use of mannitol and lithium may increase risk of lithium toxicity. If concomitant use is necessary, frequently monitor lithium concentrations and for signs of toxicity.'

Clinical monograph

How it works

It is freely filtered at the glomerulus but not reabsorbed, raising tubular fluid osmolality and obliging water and electrolytes to remain in the lumen; intravascularly it draws fluid out of the brain and other tissues down an osmotic gradient.

Prescribing in practice

  • Contraindicated in established anuria, severe heart failure or pulmonary oedema because the initial intravascular volume expansion can precipitate fluid overload; give a test dose if renal function is uncertain.
  • Administer through an in-line filter as crystals can form, and inspect the solution for crystallisation before use, warming if necessary.
  • Repeated or excessive dosing can paradoxically worsen renal function and cause dangerous hyperosmolality, so monitor and bound cumulative exposure.

Monitoring

Monitor serum and urine osmolality, electrolytes, renal function, fluid balance and, where relevant, intracranial pressure during therapy.

Counselling the patient

  • This is given by a drip in hospital under close monitoring.
  • Tell staff promptly if you become breathless or notice swelling.

Evidence & guidelines

Its osmotic action is long established in neurosurgical and ophthalmic practice, and current prescribing references and the SPC define its narrow place in therapy.

Reference: NICE Head Injury Guidelines; Neurocritical Care Society ICP Guidelines; SPC Mannitol 20%; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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