Mannitol should be avoided in which patient group?

• A. Head injury
• B. Diabetes mellitus
• C. Anuria
• D. Cisplatin chemotherapy

Answer: (C)

Mannitol is an osmotic diuretic that works only if the kidneys can filter and excrete it. It increases the osmolarity of the filtrate, pulling water into the renal tubules to be eliminated. Because of this dependency on urine production, it must be used when there is some level of renal function.

In an anuric patient, there is no urine output, so mannitol cannot be excreted. It then stays in the bloodstream, raising plasma osmolality and shifting fluids in ways that can lead to volume overload, edema (including pulmonary edema), electrolyte disturbances, and potential worsened overall volume status. For that reason, mannitol should be avoided in anuric patients.

Head injury is a common indication for mannitol to reduce intracranial pressure, so it’s appropriate there. In diabetes mellitus, the drug can still be used with caution, though it requires monitoring for fluid and electrolyte balance. In cisplatin chemotherapy, mannitol is sometimes used to promote diuresis and mitigate nephrotoxicity, so it isn’t contraindicated.