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

Exacerbation of delirium and epileptic seizures in an older man with idiopathic Parkinson's disease due to multiple prescriptions: a case report

Introduction

Parkinson's disease (PD) is a disorder characterized by motor symptoms, such as rigidity, akinesia, and resting tremor, as well as non-motor symptoms, including psychiatric manifestations and autonomic failure. The prevalence of PD increases with age, and the condition is more common in men than in women. Conversely, polypharmacy has emerged as a paramount medical concern, especially among older patients, correlating with medicines' adverse effects, interactions between medicines, frequent admissions to the hospital, and a high risk of morbidity and mortality.

Case description

We encountered an older male patient with idiopathic PD and mild renal dysfunction. Originally prescribed 14 types of medicines, including anti-PD drugs, the patient developed delirium and epileptic seizures during hospitalization. After reducing the number of medications, including amantadine, the symptoms significantly improved. This clinical course suggests that polypharmacy, in addition to PD itself, poses a significant risk of delirium and epileptic seizures, even in patients with mild renal dysfunction.

Conclusion

This report is indicative of the risk of polypharmacy and highlights the importance of citing drug interactions for a correct diagnosis in patients presenting with complex symptoms.

Central Nervous System Adverse Reactions to Amantadine Intoxication: A Case Report and Analysis of JADER

BACKGROUND/AIM

A few case reports of central nervous system (CNS) symptoms caused by amantadine intoxication have been published, detailing various types of symptoms and differing times to onset. We encountered a patient who developed CNS symptoms with amantadine. This prompted us to investigate the types, time to onset, and outcome of CNS adverse reactions to amantadine by analyzing data from a pharmacovigilance database.

PATIENTS AND METHODS

The patient was evaluated at Chutoen General Hospital, Shizuoka, Japan. Analysis was performed using the Japanese Adverse Drug Event Report (JADER) database.

RESULTS

In our case, the amantadine blood concentration was 4,042 ng/ml, i.e., in the toxic range. The time to onset was 26 days for dyskinesia and 90 days for depressed level of consciousness. Symptoms resolved when amantadine was discontinued. The JADER database contained 974 cases of adverse reactions to amantadine. The most frequently reported CNS adverse reaction was hallucination, with a reporting odds ratio of 64.28 (95% confidence interval=52.67-78.46). Positive signals were detected for all CNS adverse reactions. For all CNS reactions, clinical outcomes were poor in a comparatively low percentage of cases. Most CNS reactions occurred soon after administration of amantadine, usually within approximately one month.

CONCLUSION

Because most CNS adverse reactions to amantadine usually occur within approximately one month of initiating treatment, healthcare providers should exercise heightened vigilance in monitoring patients for such reactions during this period.

Amantadine-Induced Craniofacial Myoclonus: Distinctive Iatrogenic Dysarthria in Parkinson's Disease

Background

Amantadine is a widely prescribed medication in Parkinson's disease (PD). A distinctive craniofacial distribution of myoclonus with speech impairment is an underrecognized iatrogenic complication in amantadine-treated patients with PD.

Cases

We report 7 patients with idiopathic PD (disease duration, 6-21 years) who developed speech-induced craniofacial-predominant myoclonus with "stuttering-like" dysarthria and speech arrests days to months after amantadine initiation or dose increase. Renal insufficiency was identified as a risk factor in 4 cases. In all cases, reduction or discontinuation of amantadine markedly attenuated the myoclonus and restored speech intelligibility.

Literature Review

Amantadine can induce subcortical segmental or generalized myoclonus. A report in 1996 of "vocal myoclonus" in an amantadine-treated patient with PD was the first observation of a focal distribution of myoclonus, particularly affecting speech. Since then, few cases of craniofacial myoclonus with speech impairment have been reported, none with accompanying video. With 1 exception, the craniofacial distribution was part of a generalized pattern of amantadine-induced myoclonus. Comorbid renal insufficiency is a recognized risk factor.

Conclusions

Speech-induced craniofacial myoclonus, with marked "stuttering-like" dysarthria and speech arrests, is a disabling iatrogenic complication in PD that resolves upon amantadine discontinuation.