Background: Mirtazapine, which enhances central noradrenergic and serotonergic activity, is
a commonly prescribed drug for mood disorders in elderly patients due to the low incidence
of adverse effects. A heterocyclic antidepressant, mirtazapine has pharmacodynamics similar
to selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants. Nevertheless,
geriatric patients in general are more prone to experience adverse drug effects.
Objective: To report a case of hyponatremia in an elderly hospice patient associated with
mirtazapine use.
Case Summary: A 72-year-old Latino male with stage IV colon cancer entered into hospice
care and was treated for major depressive disorder with mirtazapine. On day 6 of treatment,
he was somnolent and confused. He was found to have severe hyponatremia (serum sodium
of 116 mmol/L) without any immediately identifiable physiologic cause. His previous sodium
levels were within normal limits over a 6-month period including when mirtazapine was
started. Upon discontinuation of mirtazapine, the patient's mental status improved, and his
sodium level returned to normal.
Discussion: Hyponatremia resulting from antidepressant use, particularly SSRIs, is rare in
the general population, but in the elderly population the incidence increases because of multiple
factors. There are few reports in the literature regarding hyponatremia induced by mirtazapine.
Conclusions: The benefit of treating mood disorders at the end of life outweighs the risks
of untreated depression. Hyponatremia, although an uncommon adverse effect of mirtazapine
therapy, should be considered in the elderly patient with altered mental status or delirium
who has recently initiated mirtazapine therapy.
