Electrolytes & Fluids

Mannitol osmotherapy

Indication-specific bolus and follow-up CRI calculator for mannitol, aligned with Plumb's: osmotic diuresis, oliguric acute kidney injury (with optional 60–120 mg/kg/hr maintenance CRI), acute glaucoma, increased intracranial pressure from cerebral edema (no CRI), and adjunctive treatment of uroliths (with fixed 1 mg/kg/min maintenance CRI). Computes total dose, volume at 20% or 25% concentration, pump rate for the bolus, and mL/hr for any maintenance CRI. Surfaces the 2 g/kg/24h cumulative ceiling and the crystallization-filter requirement.

Slow bolus, not a sustained CRI

Mannitol is given as a 15–30 min infusion, repeated up to q4–6h for cerebral edema or as a single response-test dose for oliguric AKI. The pump rate computed here is for the brief infusion window only, not for hours of sustained delivery. Cumulative dosing above 2 g/kg/24h has been associated with paradoxical worsening of cerebral edema (reverse osmotic shift) and acute kidney injury (osmotic nephrosis).

Patient weight

lb kg

Indication

Increased ICP / cerebral edema Oliguric AKI (with optional CRI) Acute glaucoma (IOP) Uroliths (bolus + 1 mg/kg/min CRI) Osmotic diuresis (label dose)

Dose (g/kg)

Published range for osmotic diuresis (label dose): 1.5–2 g/kg (typical 1.5 g/kg).

Published range for oliguric acute kidney injury: 0.25–1 g/kg (typical 0.5 g/kg).

Published range for acute glaucoma (iop reduction, refractory to topical agents): 1–2 g/kg (typical 1.5 g/kg).

Published range for increased icp: 0.5–1 g/kg (typical 0.5 g/kg).

Published range for adjunctive treatment of uroliths: 0.25–0.5 g/kg (typical 0.25 g/kg).

Concentration

20% (200 mg/mL) 25% (250 mg/mL)

20% is the most common US veterinary stock concentration. Both crystallize at room temperature; warm to body temp and use a 0.22 µm in-line filter.

Infusion duration (min)

Typical for osmotic diuresis (label dose): 30–30 min (default 30).

Typical for oliguric acute kidney injury: 15–20 min (default 20).

Typical for acute glaucoma (iop reduction, refractory to topical agents): 10–20 min (default 15).

Typical for increased icp: 15–20 min (default 20).

Typical for adjunctive treatment of uroliths: 20–20 min (default 20).

Awaiting input

Enter patient weight, dose, and infusion duration to see the result.

Reference

Formula

Total mannitol dose is a simple weight-by-dose product. Volume follows from the chosen stock concentration; pump rate divides volume by the infusion window.

$$\text{Total dose (g)} = \text{dose (g/kg)} \times \text{weight (kg)}$$

$$\text{Volume (mL)} = \frac{\text{Total dose (g)}}{\text{concentration (g/mL)}}$$

$$\text{Pump rate (mL/hr)} = \frac{\text{Volume (mL)}}{\text{duration (min)}} \times 60$$

Stock conversions: 20% mannitol = 0.20 g/mL; 25% mannitol = 0.25 g/mL.

Dose ranges by indication (per Plumb's)

Indication	Bolus dose	Duration	Repeat / CRI
Osmotic diuresis (label)	1.5–2 g/kg	30 min	Single dose
Oliguric AKI	0.25–1 g/kg	15–20 min	q4–6h OR CRI 60–120 mg/kg/hr; cap 2 g/kg/day
Acute glaucoma (IOP)	1–2 g/kg	10–20 min	Single dose; limit water intake 1–4 hr post-dose
Increased ICP / cerebral edema	0.5–1 g/kg	15–20 min	q6–8h boluses; CRI NOT recommended
Uroliths	0.25–0.5 g/kg loading	20 min	Then CRI at 1 mg/kg/min (= 60 mg/kg/hr)

Cumulative-dose ceiling

Sustained or high cumulative dosing produces two distinct paradoxical effects. In the brain, prolonged exposure allows mannitol to cross the disrupted blood-brain barrier; once inside the brain, it draws water back across by reverse osmotic shift, worsening cerebral edema. In the kidney, accumulation of mannitol in the proximal tubule produces osmotic nephrosis (vacuolation, swelling, tubular dysfunction) that mimics or worsens existing AKI.

The conventional ceiling is 2 g/kg/24h, or sustained therapy beyond 5–7 days. Serum osmolality monitoring (target <320 mOsm/kg) provides an empirical safety check that supersedes the strict cumulative dose limit.

Sources

Source citations

Plumb DC. Plumb's Veterinary Drugs. Mannitol monograph (current edition). Indication-specific dose ranges and the cumulative ceiling derive from this monograph.
Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 4th ed. St. Louis, MO: Elsevier; 2023. Ch. 88 (Traumatic Brain Injury); Ch. 117 (Acute Kidney Injury).
DiBartola SP, ed. Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 4th ed. St. Louis, MO: Elsevier Saunders; 2012. Ch. 26 (Acute Kidney Injury). Mechanism, osmotic nephrosis, and serum osmolality monitoring target.