Hyponatraemia associated with antidepressant use

Hyponatraemia can be caused by tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), serotonin and noradrenaline reuptake inhibitors (SNRIs) and monoamine oxidase inhibitors (MAOIs). Mild hyponatraemia is usually asymptomatic but patients may experience nausea and general malaise. If hyponatraemia is severe or develops rapidly, it can cause convulsions, coma or death.

Factors that further increase the risk of hyponatraemia include:

• older age
• female gender
• low body weight
• concurrent use of drugs that cause hyponatraemia (eg diuretics, NSAIDs, carbamazepine, chemotherapy)
• impaired kidney function
• comorbidities such as hypothyroidism, diabetes, chronic obstructive pulmonary disease, hypertension, stroke and head injury
• hot weather.

Routine measurement of serum sodium concentration is not required, but may be considered 3 to 4 weeks after starting treatment in patients at high risk of hyponatraemia.

If hyponatraemia occurs, see here for assessment and management. Stopping the causative drug is usually required. If the causative drug is an SSRI, subsequent rechallenge with the same or a different SSRI may be possible without recurrence of hyponatraemia.