A case of severe hyponatremia due to linezolid-induced SIADH

Hyponatremia is the most common electrolyte disorder. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the main cause of euvolemic hyponatremia and is often associated with medications or underlying diseases. Linezolid is a potent antibiotic against resistant Gram-positive microorganisms that has been associated with mild hyponatremia, yet with a mechanism different from SIADH.

We present the case of a patient who developed severe hyponatremia during treatment with linezolid for an ampicillin-resistant E. faecium bacteremia. A thorough work-up during the hyponatremia, as well as after it resolved, firmly identified SIADH as its cause. Importantly, SIADH occurred after linezolid was started and resolved after it was stopped, and a work-up for another cause of SIADH was negative, suggesting that linezolid was the cause of SIADH in this patient.

This is the second case of a linezolid-induced SIADH, diagnosed with a thorough work-up so to correctly differentiate between SIADH from other causes of hyponatremia.