Worsening of Hyponatremia With Electrolyte-Containing Beverage

Mr. A, a 47-year-old man with a history of schizophrenia of over 25 years’ duration, was hospitalized when he became psychotic after losing his medication (risperidone, 4 mg/day, and fluoxetine, 20 mg/day, since 1999). The medication was resumed, but improvement occurred slowly. At admission, his sodium level was 126 mmol/liter, and a review of his records showed levels fluctuating from 125 to 133 mmol/liter during the previous 2 years. His past medical history was otherwise unremarkable, and there was no significant history of alcohol or drug abuse.

Frequent compulsive consumption of water was observed. Other causes of hyponatremia, including hypothyroidism, renal insufficiency, adrenal insufficiency, and the syndrome of inappropriate antidiuretic hormone secretion, were ruled out. Magnetic resonance imaging of the brain revealed mild ventricular enlargement and generalized atrophy.

Attempts to limit his fluid consumption were enacted but were difficult to enforce. He was encouraged to substitute an electrolyte-containing beverage when he could not control his urge to drink water. He liked the beverage and consumed large quantities of it. Within 2 weeks, his sodium level gradually decreased to 118 mmol/liter, and he became confused and lethargic. He was then placed on closely monitored fluid restriction, and his sodium level rose to 128–134 mmol/liter, thus improving his mental status. Mr. A later revealed that he had thought that the beverage was a suitable substitute for water because of its salt content and that he could safely drink as much of it as he wanted. Thus, he had made no attempt to limit his intake.