What should I do if my patient with Parkinson's disease experiences undesirable side effects from amantadine?

Management of Amantadine Side Effects in Parkinson's Disease

For a Parkinson's disease patient experiencing undesirable side effects from amantadine, you should discontinue amantadine and consider alternative treatment options or dose reduction if the medication is still needed for symptom control.

Understanding Amantadine Side Effects

• Amantadine can cause both mild and serious side effects in patients with Parkinson's disease 1
• Common side effects include CNS symptoms (nervousness, anxiety, insomnia, difficulty concentrating, and lightheadedness) 1
• More severe side effects can include marked behavioral changes, delirium, hallucinations, agitation, and seizures 1
• These serious side effects are more commonly observed in patients with:
  • Renal insufficiency 1
  • Seizure disorders 1
  • Psychiatric disorders 1
  • Elderly patients (especially those taking 200 mg/day) 1

Options for Managing Amantadine Side Effects

Option 1: Dose Reduction

• If the patient is benefiting from amantadine but experiencing side effects, consider reducing the dose 1, 2
• For elderly patients (≥65 years), the daily dose should not exceed 100 mg for treatment 1
• For patients with renal impairment:
  • Reduce dosage for patients with creatinine clearance ≤50 mL/min 1
  • Follow package insert guidelines for specific dosage based on creatinine clearance 1
• Observe patients carefully after dose reduction to monitor for adverse reactions 1

Option 2: Discontinuation

• If side effects are severe or persist despite dose reduction, discontinue amantadine 1, 2
• Important caution: When discontinuing amantadine, taper the medication gradually rather than stopping abruptly 3
• Abrupt withdrawal has been associated with:
  • Neuroleptic Malignant Syndrome (NMS) in rare cases 2
  • Hyperthermia (documented cases of patients experiencing temperatures of 39-40°C) 3

Alternative Approaches

• If amantadine was being used for dyskinesia management, consider consultation with a movement disorder specialist for alternative options 4
• If amantadine was being used for Parkinsonian symptoms:
  • Optimize levodopa/carbidopa dosing 5
  • Consider other adjunctive therapies such as dopamine agonists 5

Monitoring After Discontinuation or Dose Reduction

• Monitor for hyperthermia or NMS symptoms for several days after discontinuation 2, 3
• If these symptoms occur, consider reintroducing amantadine at a lower dose and then tapering more gradually 3
• Observe for changes in Parkinsonian symptoms that may require adjustment of other medications 5

Special Considerations

• For patients with liver disease, exercise caution when administering amantadine 2
• For patients with seizure disorders, amantadine may increase seizure activity 1
• For patients with psychiatric symptoms, amantadine may worsen these conditions 1

Common Pitfalls to Avoid

• Failing to recognize that amantadine side effects may appear after prolonged use, not just at initiation 6
• Not considering renal function when dosing amantadine, especially in elderly patients 1
• Stopping amantadine abruptly rather than tapering gradually 2, 3
• Not monitoring plasma concentrations in high-risk patients (plasma amantadine concentrations >3000 ng/ml are associated with increased risk of adverse effects) 6