Beyond levodopa, the modern Parkinson disease therapeutic armamentarium includes dopamine agonists, MAO-B inhibitors, COMT inhibitors, amantadine, and anticholinergics — each with distinct roles in disease management. These agents address motor symptoms, motor fluctuations, and dyskinesias, and contribute to “levodopa-sparing” strategies in selected patients. This page covers the non-levodopa pharmacotherapy for PD motor symptoms.

Dopamine Agonists

Non-Ergot Agonists (Modern Use)

  • Pramipexole (Mirapex): D2/D3 selective; IR and ER formulations; 0.125 mg TID start, titrate to 1.5 mg TID.
  • Ropinirole (Requip): D2/D3 selective; IR and ER; 0.25 mg TID start, titrate higher.
  • Rotigotine (Neupro): D1/D2/D3; transdermal patch (24-hour) — convenient.
  • Apomorphine: nonselective dopamine agonist. SC injection (Apokyn) for rescue of “off” episodes; sublingual film (Kynmobi) as an alternative rescue route. ONAPGO (continuous subcutaneous apomorphine infusion) was FDA-approved in 2025 as a wearable daytime infusion for motor fluctuations in advanced PD — a non-enteral continuous-delivery option for patients with substantial OFF time, complementing levodopa-carbidopa intestinal gel (LCIG) and foslevodopa-foscarbidopa.

Ergot Agonists (Largely Replaced)

  • Bromocriptine, cabergoline, pergolide: 5-HT2B agonism → cardiac valve fibrosis risk.
  • Pergolide withdrawn for valvular disease.
  • Cabergoline still used for prolactinoma (lower PD doses); rare PD use.

Uses in PD

  • Monotherapy in younger patients (delay levodopa dyskinesia development).
  • Adjunct to levodopa for motor fluctuations.
  • Rescue (apomorphine SC, sublingual).

Adverse Effects

  • Nausea (often early; usually improves).
  • Orthostatic hypotension.
  • Sleep attacks: sudden onset of sleep; counsel about driving.
  • Excessive daytime sleepiness.
  • Peripheral edema.
  • Hallucinations, psychosis (especially in elderly, advanced disease).
  • Impulse control disorders: gambling, hypersexuality, compulsive shopping, binge eating (~14-17% of patients) — counsel patient and family; screen regularly.
  • Dopamine dysregulation syndrome: compulsive drug use.
  • Punding: stereotyped repetitive behaviors.
  • Withdrawal syndrome: dopamine agonist withdrawal syndrome (DAWS) — anxiety, depression, fatigue, sweating, restlessness; can be severe.

Restless Legs Syndrome

  • Dopamine agonists effective; gabapentinoids now often preferred first-line.
  • Augmentation: dopaminergic worsening with chronic use; emerging earlier with low-dose agonists.

MAO-B Inhibitors

Selegiline (Eldepryl, Zelapar)

  • Irreversible MAO-B inhibitor.
  • 5 mg BID; sublingual ODT formulation.
  • Symptomatic in early PD; modest motor benefit.
  • Transdermal (Emsam): higher-dose for depression; less MAO-B selective.
  • Side effects: insomnia, dyskinesia in advanced PD.

Rasagiline (Azilect)

  • Irreversible MAO-B inhibitor.
  • 1 mg daily; once-daily convenient.
  • Symptomatic + possible disease-modifying signal (ADAGIO trial; remains debated).
  • Less amphetamine-like metabolite than selegiline.

Safinamide (Xadago)

  • Reversible MAO-B inhibitor + glutamate release modulator.
  • For motor fluctuations as adjunct to levodopa.
  • 50-100 mg daily.

Considerations

  • Selective MAO-B at usual doses: less tyramine-related dietary restrictions; reduced hypertensive crisis risk vs nonselective MAOIs.
  • Caution with serotonergic drugs (theoretical serotonin syndrome; rare in practice but warning exists).
  • Discontinue 14 days before surgery to avoid anesthetic interactions.

COMT Inhibitors

Entacapone (Comtan)

  • Peripheral COMT inhibitor.
  • 200 mg with each levodopa dose; up to 1600 mg/day.
  • Reduces peripheral levodopa metabolism → extends “on” time by 30-60 min per dose.
  • Combined: Stalevo (carbidopa-levodopa-entacapone).
  • Side effects: orange urine, increased dyskinesia, diarrhea.

Opicapone (Ongentys)

  • Once-daily peripheral COMT inhibitor.
  • 50 mg evening dose.
  • Convenience advantage over entacapone.

Tolcapone (Tasmar)

  • Central + peripheral COMT inhibitor.
  • Hepatotoxicity risk → black box; LFT monitoring required.
  • Restricted use; rarely first choice.

Amantadine

  • Mechanism: increases dopamine release; NMDA antagonist; possible anticholinergic.
  • 100 mg BID; renal adjustment.
  • Main use in PD: dyskinesia management (first-line for peak-dose dyskinesias).
  • Also useful for: early symptomatic, freezing of gait (modest), reduced fatigue.
  • Adverse: livedo reticularis, peripheral edema, hallucinations, insomnia, dry mouth.
  • Amantadine ER (Gocovri, Osmolex ER): bedtime dosing; longer duration; specifically approved for dyskinesias.

Anticholinergics

  • Trihexyphenidyl (Artane): tremor.
  • Benztropine (Cogentin): tremor; drug-induced parkinsonism.
  • Effective for tremor; less effective for bradykinesia/rigidity.
  • Side effects: dry mouth, blurred vision, urinary retention, constipation, cognitive effects (avoid in elderly).
  • Reserve for young PD patients with prominent tremor; avoid in elderly.

PD Psychosis Management

  • Pimavanserin (Nuplazid): 5-HT2A inverse agonist; no D2 effect; FDA-approved for PD psychosis without worsening motor symptoms; QT prolongation.
  • Quetiapine: low-dose (12.5-50 mg) at bedtime; less D2 activity than other antipsychotics; off-label commonly used.
  • Clozapine: most effective; agranulocytosis risk; REMS monitoring; reserved for refractory.
  • AVOID: haloperidol, risperidone, olanzapine (worsen motor symptoms).
  • First step: reduce anti-PD meds (anticholinergics → amantadine → MAO-B → COMT → dopamine agonist → levodopa).

PD Dementia / DLB Cognitive Management

  • Rivastigmine (oral or transdermal): FDA-approved for PD dementia; effective in DLB.
  • Donepezil: off-label for PD dementia.
  • Memantine: data limited.

Non-Motor PD Symptoms

Autonomic Dysfunction

  • Orthostatic hypotension: fludrocortisone, midodrine, droxidopa, pyridostigmine; salt, fluid, compression.
  • Constipation: increase fluid, fiber; macrogol, lubiprostone, prucalopride (avoid metoclopramide).
  • Urinary urgency: anticholinergics (cognitive trade-off) or mirabegron.
  • Sialorrhea: glycopyrrolate, botulinum toxin to salivary glands.
  • Sexual dysfunction: PDE5 inhibitors.

Sleep Disorders

  • REM sleep behavior disorder: clonazepam, melatonin.
  • RLS: gabapentinoids, dopamine agonists.
  • Insomnia: address comorbidities; consider melatonin.
  • EDS / sleep attacks: modafinil; manage dopamine agonist dose.

Depression / Anxiety

  • SSRIs, SNRIs commonly used.
  • TCAs: avoid in elderly (anticholinergic).
  • Behavioral therapy.

Pain

  • Off-period pain: optimize levodopa.
  • Musculoskeletal: standard analgesics, PT.
  • Central pain: gabapentinoids, SNRIs.

Deep Brain Stimulation (DBS) — Pharmacologic Relevance

  • STN (subthalamic nucleus): improves motor fluctuations; allows medication reduction (~50%).
  • GPi (globus pallidus internus): less medication reduction but excellent dyskinesia control.
  • Vim (ventral intermediate thalamic): tremor-predominant PD.
  • DBS patients still need optimal medication management.
  • Programming requires pharmacology knowledge: medication reduction with stimulation.

MAO-B Inhibitor + SSRI Caveat

  • Theoretical serotonin syndrome with SSRI + selegiline/rasagiline.
  • Selective MAO-B at usual doses → low practical risk; many patients tolerate.
  • Common practice: SSRI + MAO-B inhibitor allowed with patient education.
  • Avoid: meperidine, tramadol with MAO-B inhibitor.

🔍 Did You Know?

The frequency and underrecognition of impulse control disorders (ICDs) in dopamine agonist therapy represents one of the most clinically important blindspots in modern PD management. Approximately 14-17% of PD patients on dopamine agonists develop ICDs — including pathological gambling, hypersexuality, compulsive shopping, binge eating, hoarding, or dopamine dysregulation syndrome (compulsive medication use). These behaviors are often hidden by the patient due to shame and may emerge only after significant financial, marital, or legal consequences. Risk factors include: younger age, male sex, family history of addiction, predominant motor predominantly tremor, and D3 receptor preferences (pramipexole, ropinirole are D2/D3 agonists). The clinical implications are profound: every patient and family member should be counseled before starting a dopamine agonist, with screening at each visit using validated tools (QUIP-RS). Specific questions: gambling, sexual behavior changes, compulsive shopping, eating, secret behaviors — and ask the spouse/partner who often sees what the patient denies. The lesson generalizes: dopaminergic drugs alter motivation and reward processing, not just motor function, and the cost-benefit calculation must include behavioral risks. Reducing the dopamine agonist (often with levodopa substitution) typically resolves ICDs, though some patients have persistent symptoms. For practicing neurologists, this is a non-negotiable safety conversation, and emerging strategies include cognitive behavioral therapy, naltrexone trials, and switching to lower D3 affinity agents.

Pitfalls and Pearls

  • Dopamine agonists: pramipexole, ropinirole, rotigotine; apomorphine rescue.
  • ICD warning: 14-17%; counsel patient + family; screen regularly.
  • Sleep attacks: counsel about driving.
  • DAWS: dopamine agonist withdrawal syndrome can be severe; taper slowly.
  • Ergot agonists: largely abandoned (cardiac valve fibrosis).
  • MAO-B inhibitors: rasagiline, selegiline, safinamide; mild symptomatic.
  • MAO-B + SSRI: theoretical serotonin syndrome; usually well-tolerated.
  • Entacapone: peripheral COMT inhibitor; with each levodopa dose.
  • Opicapone: once-daily COMT inhibitor; convenience.
  • Tolcapone: restricted (hepatotoxicity).
  • Amantadine: dyskinesia first-line; livedo reticularis; hallucinations.
  • Amantadine ER (Gocovri): bedtime; specifically for dyskinesias.
  • Anticholinergics: tremor only; avoid in elderly.
  • Pimavanserin: PD psychosis without motor worsening.
  • Quetiapine: low-dose; PD psychosis; off-label common.
  • Avoid in PD: haloperidol, risperidone, olanzapine, metoclopramide, prochlorperazine.
  • Rivastigmine: FDA-approved for PD dementia; transdermal option.
  • DBS: STN allows medication reduction; GPi excellent for dyskinesias.

References

  1. Bloem BR, Okun MS, Klein C. Parkinson’s disease. Lancet. 2021;397(10291):2284-2303.
  2. Voon V, Napier TC, Frank MJ, et al. Impulse control disorders and levodopa-induced dyskinesias in Parkinson’s disease: an update. Lancet Neurol. 2017;16(3):238-250.
  3. Olanow CW, Rascol O, Hauser R, et al. A double-blind, delayed-start trial of rasagiline in Parkinson’s disease (ADAGIO). N Engl J Med. 2009;361(13):1268-1278.
  4. Cummings J, Isaacson S, Mills R, et al. Pimavanserin for patients with Parkinson’s disease psychosis: a randomised, placebo-controlled phase 3 trial. Lancet. 2014;383(9916):533-540.
  5. Connolly BS, Lang AE. Pharmacological treatment of Parkinson disease: a review. JAMA. 2014;311(16):1670-1683.