Hyponatremia is an electrolyte disorder that can be caused by multiple factors, among which the syndrome of inappropriate antidiuretic hormone secretion (SIAHS) is one of the most frequent causes. Selective serotonin reuptake inhibitors (SSRIs) are the most widely used antidepressant drugs in all age groups for efficacy, safety, and adverse effects, although they can cause serious and undesirable side effects.

Report of a series of cases of patients with SIAHS secondary to the use of SSRIs.

We report 21 cases of patients between 52 and 76 years of age, of both sexes, undergoing treatment for depressive disorder with SSRI antidepressants and anxiolytics, concomitant with other clinical treatments (ACEI, thiazides, and carbamazepine). Biochemical laboratory and electrocardiogram studies were performed prior to the start of treatment.

In the first weeks (mean = 2.5) after starting psychopharmacological treatment, hyponatremia (mean = 126 mEq/L) was recorded in 9 symptomatic patients, and Inadequate Antidiuretic Hormone Secretion Syndrome (SIAHS) was diagnosed with referral to Nephrology and Endocrinology. The SSRI was withdrawn, achieving normalization of the biochemical values (plasma and urinary sodium, plasma, and urinary osmolarity), psychotherapy was reinforced until the rotation of another antidepressant. The mean time of suspension of the antidepressant was 7.1 days, the time of disappearance of symptoms after the suspension was 4.3 days and the normalization of biochemical values was 21.68 days. Only one case was severe and 5 required hospitalization.

In the cases presented, the SSRI antidepressants were associated with hyponatremia caused by the syndrome of inappropriate antidiuretic hormone secretion. This adverse event was more significant in elderly patients and in those treated with other drugs that cause the disease, such as antineoplastic, diuretic, and antiepileptic drugs, due to synergism between the causative mechanisms.

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