Selective serotonin re-uptake inhibitors are better tolerated than older antidepressant agents but are associated with side effects of which internists may not be aware. One such side effect is the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Life-threatening hyponatremia due to SIADH has been described with both fluoxetine (Prozac, Dista Products Co., Indianapolis, Indiana) [1] and paroxetine (Paxil, SmithKline Beecham Pharmaceuticals, Pittsburgh, Pennsylvania) [2]. Recently, several reports in the psychiatric literature have described the occurrence of SIADH due to another selective serotonin reuptake inhibitor, sertraline (Zoloft, Roerig, New York, New York) [3-5]. We describe an additional case of sertraline-induced life-threatening hyponatremia and wish to alert internists to this possible complication.

A 59-year-old woman with a history of depression and chest pain presented with progressive lethargy. Her medications included aspirin, metoprolol, and nitroglycerin patches, which she had been receiving for several years without incident. Three weeks before admission, the patient began receiving sertraline, 25 mg/d. Her serum sodium level was normal at that time. At hospital admission, her vital signs were normal and no edema was noted. Results of a neurologic examination did not show focal neurologic abnormalities, but the patient was lethargic and nonverbal. Her serum sodium level was 117 mEq/L, her blood urea nitrogen level was 4 mg/dL, her serum creatinine level was 0.4 mg/dL, and her urine sodium level was 189 mmol/L. The patient's serum osmolality was 233 mOsm/kg, and concurrent urine osmolality was 465 mOsm/kg. A diagnosis of SIADH was made, and sertraline was stopped. Intravenous normal saline and furosemide were started. The patient's serum sodium level returned to normal by hospital day 4, and no recurrence of hyponatremia has been noted during 7 months of follow-up.

The development of hyponatremia shortly after the start of sertraline therapy strongly implicates this drug. The onset of hyponatremia within several weeks of starting sertraline and the degree of hyponatremia are both consistent with the findings of previous reports [3-5]. Internists should be aware of the risk for hyponatremia with this class of medication, as well as other recognized side effects and drug interactions related to selective serotonin reuptake inhibitors.