Hyponatraemia, defined as serum sodium below 135 mmol/L, is a common electrolyte disturbance that ranges from asymptomatic to life-threatening. Its causes are diverse, but medications are a major contributor—particularly in elderly patients with multiple comorbidities and polypharmacy. Levodopa, a standard treatment for Parkinson’s disease, has been rarely associated with hyponatraemia, with only a few reported cases. We present the case of a 67-year-old woman with Parkinson’s disease, atrial fibrillation, hypothyroidism, and chronic hyponatraemia who developed acute symptomatic hyponatraemia secondary to co-beneldopa (levodopa/carbidopa). She was admitted following a fall that resulted in a left femoral neck fracture and underwent hemiarthroplasty. Postoperatively, she developed acute confusion associated with a significant decline in serum sodium from her baseline of approximately 125 mmol/L to 108 mmol/L. Laboratory investigations demonstrated euvolemic hyponatraemia with normal adrenal and thyroid function, consistent with the Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH). Medication review identified co-beneldopa as the most likely precipitant. Levodopa is thought to stimulate antidiuretic hormone release through dopaminergic pathways, thereby inducing SIADH-like effects. Discontinuation of co-beneldopa and transition to a rotigotine transdermal patch led to gradual normalisation of sodium levels and full neurological recovery. She was discharged home within a few days, when sodium levels returned to baseline, and review in clinic three weeks later found her well and with an improved sodium level of 132 mmol/L. This case highlights levodopa-induced hyponatraemia as a rare yet clinically significant adverse drug reaction. Awareness of this association is essential, particularly in elderly patients or those with pre-existing electrolyte disturbances. Prompt recognition and withdrawal of the causative agent can prevent serious complications. Alternative dopaminergic therapies, such as rotigotine, should be considered to ensure safe and effective management of Parkinson’s disease. Proactive medication review and individualised care remain crucial in preventing iatrogenic harm.

Haddy is a medical doctor with a master's degree in molecular pathology of cancer and bachelors degree in biomedical sciences