Amantadine-induced serotonin syndrome in a patient with renal failure

Serotonin Syndrome Precipitated by Amantadine in a Patient With Persistent Post Concussive Symptoms - A Case Report

Symptoms after mild traumatic brain injury (MTBI) can persist for greater than 1 month in up to 20% of individuals, yet there are no current medications approved by the Food and Drug Administration for treatment of specific concussion related sequelae. Amantadine, a dopamine agonist and N-Methyl-D-aspartate antagonist, is increasingly being used as a treatment option for individuals with traumatic brain injury across the spectrum of injury severity. This case report describes a 22-year-old individual who sustained an MTBI without loss of consciousness or post-traumatic amnesia after striking their head against a metal cabinet. The individual was referred to an interdisciplinary outpatient brain rehabilitation program secondary to persistent symptoms after MTBI, was prescribed amantadine for post-traumatic headache 97 days after injury, and subsequently developed symptoms of serotonin syndrome (SS) within 10 days of medication initiation. While SS caused by amantadine has been described in individuals with renal failure, this case report is the first to describe amantadine precipitating SS - confirmed by a validated diagnostic criterion and successfully treated with lorazepam and cyproheptadine - in a patient with normal renal function already on duloxetine, bupropion, and gabapentin. This case report is important in elucidating potential contributions of amantadine to the development of SS and highlighting the important role clinicians have in assessing for polypharmacy when prescribing amantadine for individuals with traumatic and acquired brain injuries.

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.

Myoclonus Secondary to Amantadine: Case Report and Literature Review

The usual adverse events of amantadine are dizziness, dry mouth, and peripheral edema. Postmarketing experience has revealed abnormal movements such as tremors, involuntary muscle contractions, and gait abnormalities. Herein, we report a case of an elderly male who presented with generalized twitching associated with amantadine. A 64-year-old male presenting with jerking movements within one day of onset was admitted. Sudden and involuntary distal lower and upper limb muscle twitching was observed. The subject presented subsequent brief movements when attempting to stand or hold arms antigravity. He was diagnosed with Parkinson's disease three years ago. Eight days before the presentation to the emergency department, he consulted with his primary care physician, who prescribed amantadine to improve his motor symptoms. On the seventh day, he developed brisk abnormal movements. Laboratory exams, neuroimaging, and electroencephalogram were unremarkable. Amantadine was discontinued. After three days, the patient reported that his jerking movements had fully recovered. To the authors' knowledge, 22 individuals with amantadine-associated myoclonus had already been reported in the literature. The pathophysiology of amantadine-induced myoclonus is probably related to serotoninergic pathways. Myoclonus secondary to amantadine was slightly more common in men. The population affected was elderly, with a mean and median age of 67.7 and 64 years.

Management of severe arterial hypertension associated with serotonin syndrome: a case report analysis based on systematic review techniques

Serotonin syndrome is thought to arise from serotonin excess. In many cases, symptoms are mild and self-limiting. But serotonin syndrome can become life threatening, when neuromuscular hyperexcitability spins out of control. Uncontainable neuromuscular hyperexcitability may lead to cardiovascular complications, linked to extreme changes in blood pressure. Currently, there is little guidance on how to control blood pressure in hyperserotonergic states. We report a case with treatment-resistant arterial hypertension, followed by a clinical review (using systematic review principles and techniques) of the available evidence from case reports published between 2004 and 2016 to identify measures to control arterial hypertension associated with serotonin syndrome. We conclude that classic antihypertensives may not be effective for the treatment of severe hypertension associated with serotonin syndrome. Benzodiazepines may lower blood pressure. Patients with severe hypertension not responding to benzodiazepines may benefit from cyproheptadine, propofol or both. In severe cases, higher cyproheptadine doses than currently recommended may be necessary.

Efficacy and safety of amantadine for the treatment of L-DOPA-induced dyskinesia

L-DOPA induced dyskinesias (LIDs) may affect up to 40% of Parkinson's disease (PD) and impact negatively health-related quality of life. Amantadine has demonstrated significant antidyskinetic effects in animal PD models and in randomized double-blind placebo-controlled trials (RCTs) in patients with PD. These effects are thought to be related to the blockade of NMDA receptors modulating cortico-striatal glutamatergic-dopaminergic interactions involved in the genesis of LIDs. There are three pharmaceutical forms of amantadine currently available in the market: an oral immediate-release (IR) formulation, which is widely available; an extended-release (ER) formulation (ADS-5102) which has been recently developed and approved by the FDA; and an intravenous infusion (IV) solution, which is not commonly used in clinical practice. RCTs with amantadine IR or ER, involving more than 650 patients have shown consistent and long-lasting reductions in LIDs. Interestingly, ADS-5102 not only reduced LIDs, but also reduced significantly at the same time the duration of daily OFF-time, a unique finding compared with other antiparkinsonian medications that usually reduce time spent OFF at the cost of worsening of LIDs. Amantadine IR might also have possible effects on other PD symptoms such as apathy or fatigue. The most common adverse reactions with amantadine are constipation, cardiovascular dysfunction including QT prolongation, orthostatic hypotension and edema, neuropsychiatric symptoms such as hallucinations, confusion and delirium, nausea and livedo reticularis. Corneal degeneration is rare but critical. In summary, amantadine immediate and extended-release are effective and safe for the treatment of LIDs.

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.