Syndrome of inappropriate antidiuretic hormone associated with tolterodine therapy

To present a case of syndrome of inappropriate antidiuretic hormone (SIADH) associated with the use of tolterodine.

An acute-care unit at a university hospital with a comprehensive program for elders.

In this case report, we present a 99-year-old female who was admitted to our unit for suspected gastrointestinal bleeding who subsequently developed hyponatremia. After the initiation of tolterodine for urinary incontinence, the patient's sodium dropped to 121 mEq/L (from a usual baseline that ranged between 128 mEq/L and 134 mEq/L). Laboratory and urinary findings revealed a serum osmolality of 220 mOsm/kg, a urinary osmolality of 340 mOsm/kg, and a urinary sodium of 101 mmol/L, suggesting a euvolemic hyponatremic state consistent with SIADH. Tolterodine therapy was promptly discontinued, and patient sodium levels normalized.

Although the etiology of SIADH is often obscure and multifactorial, clinicians should be aware that it is a major cause of hyponatremia among hospitalized elderly patients, and drug therapies must always be evaluated to prevent further complications.