Hyponatremia associated with tolterodine therapy

The case of a patient who developed hyponatremia after recent initiation of tolterodine is reported.

An 86-year-old woman arrived at the hospital due to an acute change in her mental status. The patient's daughter found her mother slumped over and stated that she was unresponsive for approximately four minutes. The admitting diagnosis was transient ischemic attack or syncope. Baseline laboratory tests revealed an abnormal basic metabolic panel, including a serum sodium concentration of 125 mmol/L and a serum chloride concentration of 88 mmol/L. The results of a complete blood count and thyroid function tests were within normal limits. Unsuccessful attempts at sodium correction included initial fluid restriction and, later, the administration of 0.9% sodium chloride injection over 24 hours. Physiological causes of hyponatremia were ruled out. The attending physician and team pharmacist reviewed the patient's medication profile for potential causes of hyponatremia. Hydrochlorothiazide, a home medication for the patient, was discontinued at hospital admission and ruled out as a cause of her hyponatremia. A documented association between lisinopril, mirtazapine, or omeprazole and hyponatremia exists in various case reports. However, per the patient's primary care physician, tolterodine was the only modification of an otherwise stable medication profile at an outpatient office visit approximately four weeks prior to admission. Once tolterodine was discontinued, the patient's hyponatremia quickly resolved. Tolterodine was discontinued on hospital day 5, and the hyponatremia was corrected by the next day.

An 86-year-old woman developed hyponatremia after recent initiation of tolterodine therapy.