Case report
Low-dose Mirtazapine Induced Hyponatraemia with Probable Syndrome of Inappropriate Antidiuretic Hormone Secretion in an Elderly Male: A Case Report
VD05-VD07
Correspondence
Suvarna Jyothi Kantipudi,
Professor, Department of Psychiatry, Sri Ramachandra Medical College and Research Institute, Porur, Chennai-600116, Tamil Nadu, India.
E-mail: suvarna@sriramachandra.edu.in
Hyponatraemia is a common and potentially serious condition in elderly patients. It is associated with significant morbidity including delirium, falls and prolonged hospitalisation. Antidepressant induced hyponatraemia is a recognised adverse effect, most commonly attributed to Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH). Although Mirtazapine is often considered a safer alternative to other antidepressant-induced hyponatraemia, reports of SIADH related to its use remain limited. We report the case of a 72-year-old male with dementia and Behavioural and Psychological Symptoms of Dementia (BPSD) who developed symptomatic hyponatraemia 15 days after initiation of mirtazapine (3.75 mg/day). Evaluation revealed hypotonic hyponatraemia with a serum sodium level of 122 mEq/L, serum osmolality of 253 mOsm/kg, urine spot sodium of 31.1 mEq/L and clinical euvolaemia. Alternative causes of hyponatraemia and SIADH including adrenal insufficiency, hypothyroidism, renal dysfunction, cardiac failure, malignancy, respiratory disease, HIV infection and acute intracranial pathology were excluded. Mirtazapine was stopped while concomitant medications were continued unchanged along with fluid restriction and high-salt diet which resulted in improvement of serum sodium levels and resolution of hyponatraemia associated delirium within three days. The likelihood of Mirtazapine use causing hyponatraemia was probable (score 7) as per the Naranjo Adverse drug reaction probability scale. This case describes probable mirtazapine-associated SIADH occurring at a low dose of 3.75 mg/day in an elderly male and highlights the importance of baseline evaluation and regular monitoring of serum sodium along with vigilance for clinical signs of hyponatraemia in elderly patients and those with risk factors receiving mirtazapine although mirtazapine is considered a safer alternative for other antidepressant-induced hyponatraemia.