Amantadine neurotoxicity in a pediatric patient with renal insufficiency

Amantadine intoxication despite moderate renal dysfunction: A case of combined use with donepezil

Amantadine intoxication occurred despite moderate renal dysfunction. This may have been affected by the use of donepezil, and we require careful attention to these combinations.

Status epilepticus in a pediatric patient with amantadine overdose

A 2-year-old boy who ingested 0.8-1.5 g of amantadine developed status epilepticus. One hour later, the child presented with agitation, diaphoresis, and vomiting. He was admitted to the pediatric emergency department 2 hours later. Generalized seizures evolved to status epilepticus, with alternating generalized tonic-clonic and partial seizures, over a period of 7 hours. Other initial clinical signs were sinusal tachycardia and reactive bilateral mydriasis. All symptoms resolved within 20 hours, with a good recovery; the child was released from the hospital on day 3.

Cardiotoxicity after massive amantadine overdose

INTRODUCTION

Amantadine hydrochloride is an antiviral medication used as therapy for parkinsonism and as a cognitive enhancer. We report 2 cases of massive, acute ingestion of amantadine hydrochloride confirmed with serial serum levels.

CASE REPORTS

A 47-year-old woman presented to the emergency department (ED) 30 minutes after ingesting 10 g of amantadine (150 mg/kg) by her report. Initial ECG revealed a sinus rhythm with rate of 93 bpm, and a QRS of 84 msec. While in the ED, the patient sustained a pulseless cardiac arrest and the monitor revealed ventricular tachycardia. She was successfully defibrillated. Postdefibrillation ECG showed a sinus rhythm (rate = 82 bpm), QRS of 236 msec, and QTc of 567 msec. The serum potassium was 1.0 mEq/L (1.0 mmol/L). The patient was given 300 ml (300 cc) 3% sodium chloride IV over 10 minutes. Ten minutes after completion of the hypertonic saline infusion, the patient's ECG abnormalities resolved and the QRS was 88 msec. Her potassium was repleted over the next 11 hours postpresentation, and she also received an IV bolus of 4 g of magnesium sulfate immediately after the cardiac arrest. No further hypotension, dysrhythmia, conduction delay, or ectopy was noted during the patient's hospital stay. The second case involved a 33-year-old female patient who presented 1 hour after ingesting 100 tablets of amantadine hydrochloride (100 mg/tab). Initial ECG revealed sinus tachycardia with a QRS of 113 msec, an R wave in lead aVR of 4-5 mm and a QTc of 526 msec. Her serum potassium was 3.0 mEq/L (3.0 mmol/L), her serum calcium was 9.4 mg/dl (2.35 mmol/L), and serum magnesium was 2.1 mg/dl (0.86 mmol/L) on labs drawn at initial presentation. The patient was intubated for airway protection, and her potassium was repleted and corrected over the next 9 hours. Her ECG abnormalities improved 8 hours after initial presentation and normalized at approximately 14 hours postingestion. The patient was discharged home 11 days after her ingestion.

CONCLUSION

Acute amantadine toxicity manifests with life-threatening cardiotoxicity. Concurrent, often profound, hypokalemia may complicate the administration of sodium bicarbonate in the management of cardiac dysrhythmias.

Amantadine-induced coma

Amantadine has found use primarily as an antiviral agent and in the symptomatic treatment of parkinsonism. However, the use of amantadine for the subjective alleviation of fatigue in multiple sclerosis and in the treatment of agitated aggressive behavior in the traumatic brain injured patient has also been described. Side effects of amantadine are primarily related to the central nervous system and include hallucinations, confusion, and nightmares. Toxic manifestations include acute psychosis, coma, cardiovascular toxicity, and death. Amantadine toxicity is a particular problem in patients with renal insufficiency because 90% of an oral dose is excreted unchanged in the urine. We present a case of amantadine-induced coma in a patient with multiple sclerosis and end-stage renal disease. Moreover, this degree of amantadine toxicity was profoundly apparent at a drug level usually not associated with such a severe presentation.