Medication for Parkinson disease

There are many pharmacologic options available for the treatment of Parkinson disease, and regimens are individualized depending on the patient's age, symptoms, and symptom severity. However, currently, only symptomatic treatment is possible, though drugs which may slow or reverse the course of the disease are currently being investigated. Since treatment of Parkinson disease at an early stage can significantly improve a patient's subjective well-being (honeymoon period), medical therapy should be initiated as soon as symptoms begin to interfere with the patient's daily life. For most patients, first-line treatment consists of levodopa (L-DOPA) or dopamine receptor agonists, such as ropinirole and pramipexole. Other drugs that are used to treat Parkinson disease include amantadine, MAO-B inhibitors, and COMT inhibitors.

Substance class		Agent	Mode of action	Indication		Additional information
Dopamine precursors		L-DOPA (levodopa)	L-DOPA is converted to dopamine by DOPA decarboxylase at the presynaptic neuron → direct dopaminergic effect (especially at D2 receptors) Predominantly controls bradykinetic symptoms	First-line treatment for patients > 65 years of age or patients with comorbidities Second-line treatment choice for refractory disease: Jejunal tube for L-DOPA administration or subcutaneous apomorphine Second-line treatment for patients < 65 years of age		Mostly given as monotherapy in combination with decarboxylase inhibitors Most effective drug for reducing symptoms However, increased risk of severe motor dysfunction with long-term use (see “Side effects” below) Administer between meals (e.g., 30 minutes before a meal) to increase gastrointestinal absorption (→ avoid high-protein diets)
Decarboxylase inhibitors		Carbidopa	Decreased peripheral conversion of L-DOPA to dopamine → reduced peripheral side effects of L-DOPA (e.g., orthostatic hypotension, nausea and vomiting)			Always administered together with L-DOPA
Dopamine agonists	Non-ergot	Ropinirole Pramipexole Apomorphine Rotigotine	Act directly at striatal dopamine receptors Predominantly control bradykinetic symptoms	First-line treatment for patients < 65 years of age		Less effective than L-DOPA, but fewer side effects Effective in advanced disease stages
	Ergot	Bromocriptine		Second-line treatment for patients < 70 years of age
COMT inhibitors		Entacapone Tolcapone	Inhibition of the peripheral (entacapone) or central (tolcapone) catechol-O-methyl transferase (COMT) → ↓ metabolization of dopamine → ↑ dopamine effect → ↓ demand for L-DOPA and longer therapeutic effect for each dose	Entacapone: If L-DOPA loses effect or motor symptoms fluctuate during L-DOPA therapy Tolcapone: for refractory Parkinson disease		Monotherapy with COMT inhibitors is ineffective → should always be combined with L-DOPA and carbidopa
NMDA antagonists		Amantadine	Acts antagonistically at the glutamate N-methyl-D-aspartate (NMDA) receptor → dopaminergic effect Mostly controls bradykinetic symptoms	Short-term treatment of mild symptoms Drug of choice during akinetic crisis Reduction of L-DOPA-induced dyskinesia		Loss of effect after several months of treatment → cannot be used for long-term therapy May have cardiac side effects (prolonged QT interval)
MAO-B inhibitors		Rasagiline Safinamide Selegiline	Inhibition of MAO-B → decreased dopamine metabolization in the brain → prolonged dopamine effect → ↓ demand for L-DOPA	Alternative to L-DOPA or dopamine agonists for short-term therapy in patients with mild symptoms in early disease stages		The combination of L-DOPA and selegiline may reduce motor fluctuations.
Anticholinergic drugs (muscarinic antagonists)		Benztropine Trihexyphenidyl Biperiden	Inhibition of excitatory cholinergic neurons → ↓ concentration of acetylcholine	Useful as monotherapy in patients < 65 years with tremor as the main complaint May be used as an adjunct if tremor is not sufficiently controllable with standard treatment		Usually avoided in patients > 65 years because they are more prone to anticholinergic side effects (e.g., urinary retention, delirium, constipation)

Patients who do not respond to levodopa therapy will not respond to dopamine agonist therapy!

References:^{[1][2][3][4][5]}

L-DOPA (in combination with carbidopa)

• Loss of effect (may require a shorter interval between doses)
• Vegetative symptoms: : nausea and vomiting
• Psychotic symptoms
  • Hallucinations (often visual) , insomnia, anxiety, and aggressive behavior → treat with clozapine
  • Increased risk in elderly patients, women, concurrent dementia or other psychiatric disorders (e.g., depression), long duration of levodopa treatment, and high doses
• Motor fluctuations
  • Hypokinesia
    • End-of-dose akinesia/wearing-off phenomenon
    • Freezing
    • On-off phenomenon
  • Dyskinesia (hyperkinesia)
    • On-period dystonia
    • Off-period dystonia
    • Diphasic dyskinesias
• Akinetic crisis
  • Definition: : condition caused by severe dopamine deficiency (e.g., after discontinuation of L-DOPA therapy or insufficient L-DOPA absorption)
  • Clinical features: : complete inability to move , incomprehensible speech, possibly hyperthermia → increased risk of dehydration, deep-vein thrombosis, and pneumonia
  • Treatment: : intensive medical care, volume substitution, administration of L-DOPA, apomorphine, amantadine

Dopamine agonists

• Side effects common to all dopamine agonists
  • Vegetative: nausea; , vomiting, orthostatic hypotension; , dizziness, increased daytime drowsiness and sleep attacks
  • Motor function: dyskinesia (rare)
  • Psychiatric: unrest, hallucinations; , impulse control disorders (e.g., compulsive gambling, sexual activity, or shopping), psychosis
  • Dopamine agonist withdrawal syndrome
    • Etiology: : abrupt discontinuation of dopamine agonist therapy
    • Clinical features: : similar to malignant hyperthermia and neuroleptic malignant syndrome → hyperthermia; and rigor; akinesia; reduced vigilance; increased creatine kinase levels, transaminases, and leukocytes
    • Treatment: : intensive medical care, volume substitution, administration of L-DOPA, apomorphine, amantadine
• Side effects of ergotamine-derived agonists (e.g., bromocriptine)
  • Fibrosis: cardiac fibrosis, Raynaud's disease, pleural pulmonary fibrosis and retroperitoneal fibrosis

Other substances

• NMDA antagonists (amantadine)
  • Side effects similar to L-DOPA, but much less pronounced
  • Livedo reticularis, peripheral edema

NMDA antagonist can cause prolonged QT intervals! Do not administer NMDA antagonists to patients with a history of cardiac disorders!

• MAO-B inhibitors
  • Headache; , dyskinesia; , psychological disorders (e.g., hallucinations)
  • Inhibition of MAO-A with higher doses; → reduced peripheral degradation of catecholamines → adrenergic side effects (e.g., tachycardia, sweating, nervousness)
• Muscarinic antagonists (anticholinergics): see antimuscarinic side effects

Administration of antimuscarinic drugs to patients with mental disorders or delirium will likely worsen psychiatric symptoms!

• COMT inhibitors
  • Gastrointestinal side effects
  • Dyskinesia and psychiatric symptoms (e.g., hallucinations or confusion)

References:^[6][7]

We list the most important adverse effects. The selection is not exhaustive.