How can Sinemet (carbidopa-levodopa) be tapered in a patient with drug-induced parkinsonism?

Tapering Sinemet in Drug-Induced Parkinsonism

For drug-induced parkinsonism from antipsychotics, Sinemet (carbidopa-levodopa) should be tapered and discontinued, with amantadine being the preferred treatment option.

Understanding Drug-Induced Parkinsonism

Drug-induced parkinsonism is a common side effect of antipsychotic medications due to their dopamine-blocking properties. Unlike idiopathic Parkinson's disease, this condition:

• Is reversible upon discontinuation of the offending agent
• Often responds better to amantadine than to levodopa therapy
• Can worsen with continued antipsychotic use despite Sinemet treatment

Sinemet Tapering Protocol

When transitioning from Sinemet to amantadine for drug-induced parkinsonism, follow this tapering schedule:

1. Initial phase (Weeks 1-2):

   • Reduce Sinemet 10-100 from BID to once daily (preferably morning dose)
   • Start amantadine at 100 mg daily

2. Middle phase (Weeks 3-4):

   • Reduce Sinemet to 1/2 tablet (5-50 mg) once daily
   • Increase amantadine to target dose (typically 100 mg twice daily)

3. Final phase (Week 5):

   • Discontinue Sinemet completely
   • Continue amantadine at therapeutic dose

This gradual taper minimizes withdrawal symptoms and allows for assessment of response to amantadine. A decrease of 10% of the original dose per week is generally recommended for medication tapers 1.

Rationale for Amantadine

Amantadine is preferred for drug-induced parkinsonism because:

1. It works through non-dopaminergic mechanisms (NMDA receptor antagonism)
2. It doesn't interact with antipsychotics' therapeutic effects
3. It has established efficacy for drug-induced movement disorders

Monitoring During Transition

During the tapering process, monitor for:

• Worsening of parkinsonian symptoms (rigidity, tremor, bradykinesia)
• Emergence of withdrawal symptoms
• Response to amantadine therapy

If symptoms worsen significantly during tapering, slow the taper rate to 10% per month rather than per week 1.

Special Considerations

• For elderly patients: Consider a slower taper (10% reduction every 2 weeks) due to increased sensitivity to medication changes
• For patients with severe symptoms: Ensure amantadine reaches therapeutic levels before significant Sinemet reduction
• For patients with renal impairment: Adjust amantadine dosing appropriately as it is primarily renally cleared

Important Cautions

1. Abrupt discontinuation of Sinemet in drug-induced parkinsonism can lead to temporary worsening of symptoms
2. Sinemet is generally not the preferred treatment for drug-induced parkinsonism and should be discontinued when possible
3. If the patient cannot tolerate amantadine, consider alternative agents like anticholinergics (trihexyphenidyl) or switching to an antipsychotic with lower risk of extrapyramidal symptoms

The transition from Sinemet to amantadine represents the most evidence-based approach to managing drug-induced parkinsonism while maintaining control of the patient's psychiatric symptoms.