Objective: To report a case of possible theophylline-induced hyponatremia due to the syndrome of inappropriate antidiuretic hormone (SIADH).
Case summary: An 88-year-old man developed severe symptomatic hyponatremia (serum sodium 112 mEq/L) associated with inappropriate natriuresis (urinary sodium 58 mEq/L) temporally related to the initiation of theophylline. The patient fulfilled the criteria for the diagnosis of SIADH after all other causes of hyponatremia were excluded. Furthermore, no other drugs or conditions that could have evoked SIADH were found.
Discussion: Theophylline has rarely been associated with hyponatremia. A thiazide-like action of the drug on the stimulation of SIADH could be the underlying mechanism for SIADH.
Conclusions: Theophylline should be considered as a possible cause of hyponatremia.