Pramipexole-Induced Hyponatremia: A Rare but Potentially Symptomatic and Treatment-Resistant Effect at Low Doses

Introduction: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a rare side effect of pramipexole. It has been previously reported in patients taking high doses of pramipexole, with resolution following dose reduction. In our case, the patient developed symptomatic hyponatremia while on a low dose, which was resistant to correction despite multiple aggressive interventions, including hypertonic saline and loop diuretics. Hyponatremia is only resolved after discontinuation of pramipexole. Case Description: A 74-year-old female with atrial fibrillation, Hodgkin's lymphoma, and stage IIIB vulvar squamous cell carcinoma (SCC) successfully treated, presented to the emergency room with lethargy, found to have severe hyponatremia, with a serum sodium (Na) of 123 mmol/L, down from 137 mmol/L prior to admission. Laboratory workup revealed a urine osmolality of 952 mOsm/kg and a urineNa of 12 mmol/L, along with a newly reduced ejection fraction (EF). The patient was treated with 3% hypertonic saline and loop diuretics. Despite these interventions, both her mental status and serum Na failed to improve. In fact, her Na level worsened reaching a nadir of 117 mmol/L. Serum Na and mental status remained refractory to correction until pramipexole 0.5 mg daily was discontinued. Following discontinuation, serum Na gradually normalized and remained stable without further hyponatremia treatment. Discussion: Pramipexole-induced SIADH is rare. While asymptomatic hyponatremia has been reported to resolve with dose reduction, our case is notable because the patient had multiple risk factors for developing hyponatremia and was taking only a low dose of pramipexole, yet presented with symptomatic and treatment-resistant hyponatremia. This outcome was unexpected given the low dose and the rarity of pramipexole as a causative agent. Our case suggests that even low-dose pramipexole can lead to clinically significant, treatment-resistant hyponatremia, especially in patients with underlying risk factors. This can prolonged hospital stays and increased morbidity. Therefore, in patients taking pramipexole who present with hyponatremia—regardless of dosage—clinicians should maintain a high index of suspicion and consider prompt evaluation and potential discontinuation of the medication as part of the treatment strategy.