Published: 6 June 2024


Medicine-induced hyponatraemia: increased risks in older people

Published: 6 June 2024
Prescriber Update 45(2): 34–36
June 2024

Key messages

  • Hyponatraemia (low serum sodium levels) is a common electrolyte disturbance in older people.
  • Medicine use is a common cause of hyponatraemia.
  • Due to a combination of risk factors, older people are more susceptible to hyponatraemia. Use medicines that may cause hyponatraemia with caution in older people.

The Centre for Adverse Reactions Monitoring (CARM)/Medsafe recently received a report where an older person experienced severe hyponatraemia shortly after starting a selective serotonin reuptake inhibitor (SSRI). The person was also taking furosemide (report ID 153509).

This article is a reminder about medicine-induced hyponatremia and risks in older people.

Hyponatraemia may be asymptomatic

Hyponatraemia (low levels of serum sodium) is a common electrolyte disturbance, especially in older people. It is defined as a serum sodium concentration of less than 135 mmol/L.1

Hyponatraemia signs and symptoms range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma).2 Hyponatraemia may also be asymptomatic.3

In older people, hyponatraemia can be associated with cognitive impairment, gait disturbances and falls and fractures.2

How ageing contributes to an increased risk of hyponatraemia

Age-related decline in renal function, urinary concentrating ability and changes to homeostatic mechanisms can contribute to the development of hyponatraemia.3 However, there are usually multiple factors implicated in the development of hyponatraemia in older people.3

  • Comorbidities: Many conditions that are known to cause hyponatraemia are prevalent in the older population including congestive heart failure, chronic kidney disease, neurological disease, diabetes, hypothyroidism and malignancy.2,3
  • Medicines: Medicines that cause hyponatraemia are often prescribed to older people, such as diuretics, selective serotonin reuptake inhibitors (SSRIs), antipsychotics and carbamazepine.2,3
  • Polypharmacy: Use of higher doses or multiple medicines increases the risk of medicine-induced hyponatraemia.3

Other risk factors in older people include female gender, low body mass and low baseline serum sodium.3

New Zealand reports

Between 2000 and 2023 Medsafe and CARM received 288 reports of hyponatraemia, of which, 208 reports were in people aged over 65 years.

Table 1 outlines the most frequently reported suspect medicines (by medicine class) for the hyponatraemia reports in people aged over 65 years.

Table 1: Hyponatraemia reports in people aged over 65 years: Most frequently reported suspect medicines, by class, 1 January 2000 to 31 December 2023

Medicine class Suspect medicine Number of reports
Diuretics Bendroflumethiazide 35
Chlortalidone 8
Proton pump inhibitor Omeprazole 22
Antidepressants Citalopram 19
Fluoxetine 14
Paroxetine 9
Escitalopram 6
Venlafaxine 7
Antiepileptic Carbamazepine 8
Angiotensin II receptor inhibitors Cilazapril 6
Antibiotics Trimethoprim 6
Other Colecalciferol 12

Source: New Zealand Pharmacovigilance Database

Prescribing considerations

Many medicines can cause hyponatraemia. Check the medicine data sheet for further information. When prescribing to older people, consider the following for medicines that are known to cause hyponatraemia.

  • Use with caution.3
  • If using a combination of medicines that cause hyponatraemia, consider lower doses or use alternative treatment options.3
  • Most cases of medicine-induced hyponatremia occur within the first few weeks. However, hyponatraemia may also occur later in treatment if other risk factors for hyponatraemia develop or during concurrent illness.3
  • Check plasma sodium levels before and shortly after starting treatment.3 Continue to monitor plasma sodium levels closely throughout treatment as clinically indicated.
  • If medicine-induced hyponatraemia occurs, manage the patient’s sodium levels and stop the suspected medicine if clinically indicated.3,4

Further information


  1. bpacnz. 2011. A primary care approach to sodium and potassium imbalance. Best Tests September 2011. URL: (accessed 11 April 2024).
  2. Adrogué HJ, Tucker BM, Madias NE. 2022. Diagnosis and management of hyponatremia: a review. JAMA 328(3): 280–91. DOI: 10.1001/jama.2022.11176 (accessed 11 April 2024).
  3. Filippatos TD, Makri A, Elisaf MS, et al. 2017. Hyponatremia in the elderly: challenges and solutions. Clinical Interventions in Aging 12: 1957–65. DOI: 10.2147/CIA.S138535 (accessed 11 April 2024).
  4. Jacob P, Dow C, Lasker SS, et al. 2019. Hyponatraemia in primary care. The BMJ 365: l1774. DOI: 10.1136/bmj.l1774 (acessed 9 May 2024).
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