Hyponatraemia, defined as the concentration of sodium in blood serum <135 mmol/l, is the most common disorder of water and electrolyte management in clinical practice. Hyponatraemia affects approximately 15–20% of patients hospitalized for emergency indications and up to 20% of critically ill patients. It can lead to a wide range of clinical symptoms, from mild to severe,and even life-threatening and associated with increased morbidity and mortality and prolonged hospitalization of patients with many different medical conditions. Elderly patients are at high risk for hyponatraemia because age is a strong independent risk factor for hyponatraemia. In older patients, when drugs suspected of inducing hyponatraemia are used, polypharmacy should be avoided, the use of the lowest effective doses of medications or the introduction of an alternative treatment regimen is preferred.

Keywords: hyponatraemia, ADH – Antidiuretic hormone, SIADH – Syndrome of inappropriate antidiuretic hormone secretion, drug-related side effect, elderly.