Severe Delirium Caused by Short-Term Administration of Compound Paracetamol and Amantadine Hydrochloride Capsules in an Elderly Patient With Extremely Low Body Weight

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This study aimed to investigate the clinical characteristics, underlying mechanisms, and management strategies for severe central nervous system (CNS) toxicity caused by amantadine-containing compound cold medication in elderly patients with extremely low body weight. We report the case of an 83-year-old male patient weighing 37 kg (BMI 13.6 kg/m2) with a normal estimated glomerular filtration rate (eGFR), who presented with severe delirium, visual hallucinations, stereotyped behaviors, and aggressive actions after self-medicating with compound paracetamol and amantadine hydrochloride capsules (cumulative amantadine dose 800 mg) for five days to treat an upper respiratory tract infection. Detailed history-taking, physical examination, and auxiliary tests excluded alternative causes. Following medication discontinuation, full fluid replacement, and symptomatic treatment with low-dose olanzapine (2.5-5 mg/day), the patient's mental and behavioral symptoms completely resolved by day 11, with the Nursing Delirium Screening Scale (Nu-DESC) score decreasing from 10 to 0. The Naranjo score of 7 indicated that the adverse reaction was very likely related to amantadine. Advanced age (≥80 years) and extremely low body weight (BMI<15 kg/m2) may be key risk factors for amantadine-induced CNS toxicity. These factors can lead to rapid drug accumulation, even in patients with normal renal function. Therefore, clinicians should exercise caution in prescribing amantadine-containing medications to high-risk populations and enhance medication safety education.