OSMITROL 20% IN WATER
Clinical safety rating: caution
Comprehensive clinical and safety monograph for OSMITROL 20% IN WATER (OSMITROL 20% IN WATER).
Osmotic diuretic that increases plasma osmolality, drawing water from intracellular spaces into extracellular fluid and increasing renal tubular osmotic pressure, which inhibits water reabsorption and promotes diuresis.
| Metabolism | Not metabolized; excreted unchanged by the kidneys via glomerular filtration with minimal tubular reabsorption. |
| Excretion | Primarily renal excretion as unchanged drug. Over 90% of administered dose is excreted unchanged in urine within 24 hours. Less than 5% is metabolized in the liver; negligible biliary/fecal elimination. |
| Half-life | 0.25–1.5 hours (15–90 minutes) in patients with normal renal function. In oliguric or anuric patients, half-life is markedly prolonged, up to 36 hours, due to reduced clearance. |
| Protein binding | Negligible (<5%); essentially unbound. |
| Volume of Distribution | Approximately 0.3–0.6 L/kg. Mannitol distributes primarily in extracellular fluid; does not cross cell membranes readily unless administered in large doses or under pathological conditions (e.g., disrupted blood-brain barrier). Increased Vd may indicate expanded extracellular volume. |
| Bioavailability | Intravenous: 100%. Oral: Not applicable; not administered orally due to poor absorption and osmotic diarrhea. Other routes (e.g., subcutaneous or intramuscular) are not clinically relevant. |
| Onset of Action | Intravenous: Onset of diuresis occurs within 1–3 hours after infusion. Reduction of intracranial pressure (ICP) occurs within 15–60 minutes after administration. |
| Duration of Action | Diuresis lasts approximately 1–4 hours after infusion stops. Reduction of ICP persists for 3–8 hours, with a rebound effect possible after discontinuation (particularly following prolonged use). |
1-2 g/kg (5-10 mL/kg of 20% solution) intravenously over 30-60 minutes for reduction of intracranial pressure; may repeat every 6-8 hours. For preoperative bowel preparation, 100-200 mL (20% solution) orally.
| Dosage form | INJECTABLE |
| Renal impairment | Contraindicated in anuria or severe renal impairment (CrCl < 30 mL/min). Use with caution if CrCl < 50 mL/min; monitor serum osmolality and urine output. No specific dose adjustment guidelines exist; consider alternative therapy. |
| Liver impairment | No specific adjustment required for hepatic impairment. Use with caution in severe liver disease due to risk of fluid overload. |
| Pediatric use | For reduction of intracranial pressure: 0.25-1 g/kg (1.25-5 mL/kg of 20% solution) intravenously over 30-60 minutes, repeated every 6-8 hours as needed. Maximum dose: 2 g/kg/day. |
| Geriatric use | Start at lower end of dosing range (0.5 g/kg) due to increased risk of renal impairment and hypovolemia. Monitor serum electrolytes, osmolality, and renal function closely. Avoid in patients with significant cardiovascular disease. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for OSMITROL 20% IN WATER (OSMITROL 20% IN WATER).
| Breastfeeding | It is unknown if mannitol is excreted in human milk. Given its high molecular weight and low lipid solubility, excretion is likely minimal but not confirmed. Caution is advised; use only if clearly needed. M/P ratio is not available. |
| Teratogenic Risk | Osmitrol 20% is a hyperosmolar agent used for osmotic diuresis. Based on animal studies and human data, mannitol crosses the placenta. In the first trimester, there is a theoretical risk of fetal osmotic shifts, but no well-controlled studies exist. In the second and third trimesters, use may cause fetal dehydration and electrolyte disturbances. Due to its limited indications in pregnancy (e.g., for elevated intracranial pressure), the risk-benefit must be carefully evaluated. Mannitol is assigned to FDA Pregnancy Category C. |
■ FDA Black Box Warning
No FDA boxed warning.
| Serious Effects |
["Anuria due to severe renal disease","Severe pulmonary congestion or pulmonary edema","Severe dehydration","Intracranial hemorrhage (unless during craniotomy) or active intracranial bleeding","Hypersensitivity to mannitol or any component of the formulation"]
| Precautions | ["Risk of pulmonary edema or congestive heart failure due to volume expansion","May cause electrolyte imbalance (e.g., hyponatremia, hyperkalemia) and dehydration","Monitor renal function; contraindicated in anuria or severe renal impairment","May increase intracranial pressure rebound effect","Use with caution in patients with severe hypovolemia or electrolyte disorders","Intravenous administration requires careful monitoring of fluid and electrolyte status"] |
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| Fetal Monitoring | Monitor maternal serum electrolytes, osmolality, renal function (BUN, creatinine), and fluid balance (intake/output). Assess for signs of dehydration, hypernatremia, or hypokalemia. Fetal monitoring includes heart rate tracings and assessment of amniotic fluid volume (due to risk of oligohydramnios). In advanced pregnancy, consider non-stress test or biophysical profile. |
| Fertility Effects | Mannitol is not known to affect fertility. No reproductive toxicity studies specific to mannitol have demonstrated adverse effects on fertility in animal models. |