What is the muscle‑relaxant of choice for a patient with Parkinson disease who is already receiving levodopa and amantadine?

Muscle Relaxant Selection in Parkinson's Disease

Baclofen is the preferred muscle relaxant for patients with Parkinson's disease on levodopa and amantadine, as tizanidine (the most commonly used centrally-acting muscle relaxant) should be avoided due to significant sedative and hypotensive effects that can worsen Parkinsonian symptoms and increase fall risk. 1

Why Avoid Tizanidine

• Tizanidine carries substantial risks in Parkinson's patients, particularly those already on multiple medications like levodopa and amantadine, due to its profound sedative and hypotensive effects 1
• The American Academy of Neurology specifically warns against tizanidine use in elderly patients (the typical Parkinson's demographic) because of these adverse effects 1
• Sedation from tizanidine can worsen the cognitive symptoms already present in many Parkinson's patients and significantly increase fall risk 1
• The hypotensive effects are particularly problematic since orthostatic hypotension is already a common issue in Parkinson's disease, and both levodopa and amantadine can contribute to blood pressure instability 2

Preferred Alternative: Baclofen

• The American Geriatrics Society specifically recommends baclofen over tizanidine when true muscle spasm is present, noting that traditional muscle relaxants like tizanidine have nonspecific effects not truly related to muscle relaxation 1
• Baclofen works through GABA-B receptor agonism and has a more favorable side effect profile in neurodegenerative disease patients 1
• Baclofen does not interfere with dopaminergic pathways, making it safer in patients already on levodopa and amantadine 1

Critical Drug Interaction Considerations

• Amantadine itself has muscle relaxant properties through NMDA receptor antagonism and is already being used in this patient for dyskinesia management 2, 3
• Amantadine can decrease levodopa-induced dyskinesias and has mild symptomatic benefit for Parkinson's symptoms 3, 4
• Adding another centrally-acting agent like tizanidine creates additive CNS depression and polypharmacy risks 1

Common Pitfall to Avoid

• Do not reflexively prescribe tizanidine (the most commonly prescribed muscle relaxant in general practice) without considering the specific vulnerabilities of Parkinson's patients on complex medication regimens
• If muscle spasticity is related to rigidity from Parkinson's disease itself rather than true muscle spasm, optimizing the existing antiparkinsonian regimen may be more appropriate than adding a muscle relaxant 2, 3

Monitoring if Baclofen is Used

• Start at low doses (5 mg two to three times daily) and titrate slowly 1
• Monitor for muscle weakness, urinary function changes, and sedation 1
• Avoid abrupt discontinuation due to risk of withdrawal symptoms 1