Amantadine induced syndrome of inappropriate antidiuretic hormone secretion in patient of Parkinsonism

Abstract Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is an uncommon but clinically significant adverse effect associated with certain medications, including amantadine. We report a case of a 57-year-old female with Parkinsonism for 14 years, on Levodopa–Carbidopa and chronic amantadine therapy, and known hypothyroidism on thyroxine replacement. She presented with headache, nausea, generalized weakness, and one episode of generalized seizure. Laboratory evaluation revealed marked hyponatremia, and clinical assessment fulfilled the diagnostic criteria for SIADH. Other potential causes, including hypothyroidism, were excluded. Amantadine-induced SIADH was suspected. Discontinuation of amantadine along with supportive management, including fluid restriction and gradual sodium correction, resulted in both clinical and biochemical recovery. This case highlights the need for clinician awareness of the risk of SIADH with amantadine, particularly in elderly patients with multiple comorbidities, to facilitate early recognition and prevent serious complications.