Antiparkinsonism drugs: replace dopamine, mimic it, or reduce its breakdown
Parkinson disease causes bradykinesia plus tremor and/or rigidity, with non-motor symptoms also common. Medicines improve symptoms but do not replace exercise, physiotherapy, falls prevention, speech/swallow support and assessment for depression, dementia and autonomic dysfunction. Treatment is individualised to age, functional impairment, cognition and risk of dyskinesia or impulse-control disorder.
Never stop dopaminergic therapy abruptly
Sudden withdrawal can cause severe rigidity, fever, autonomic instability and a neuroleptic-malignant-like syndrome. If a patient is nil by mouth, vomiting or admitted for surgery, get urgent specialist/pharmacy advice on an alternative route.
1. Drug classes
| Class | Examples | Use and major issue |
|---|---|---|
| Levodopa + decarboxylase inhibitor | Levodopa/carbidopa; levodopa/benserazide | Most effective symptomatic therapy; later motor fluctuations/dyskinesia may occur. |
| Dopamine agonists | Pramipexole, ropinirole, rotigotine | Can reduce off time but cause sleepiness, hallucinations, oedema and impulse-control disorders. |
| MAO-B inhibitors | Selegiline, rasagiline | Reduce dopamine metabolism; review serotonergic and sympathomimetic interactions. |
| COMT inhibitors | Entacapone, opicapone | Extend levodopa effect; can worsen dyskinesia and cause diarrhoea/discolouration of urine. |
| Antimuscarinics | Trihexyphenidyl, benztropine | Occasional tremor role in younger people; avoid in older adults/cognitive impairment because confusion, urinary retention and constipation are common. |
| Amantadine | Amantadine | May help dyskinesia; adjust in renal impairment and monitor hallucinations/livedo oedema. |
2. Dose-titration examples
| Medicine | Indicative adult starting approach | Monitor |
|---|---|---|
| Carbidopa/levodopa immediate release 25/100 mg | One tablet orally three times daily is a common label-based initial regimen; increase gradually to response. Product labels may allow up to eight 25/100 tablets/day, but specialist titration is usual. | Nausea, postural hypotension, hallucinations, dyskinesia, wearing off; timing with protein-rich meals may matter. |
| Pramipexole | Start low and titrate gradually; regimen differs by indication/formulation and renal function. | Sleep attacks, hallucinations, oedema and new gambling, shopping, hypersexuality or binge eating. |
| Entacapone | Given with individual levodopa doses in protocol-directed regimens; do not add it without reviewing total levodopa exposure. | Dyskinesia (often requires levodopa reduction), diarrhoea and interactions. |
3. Managing wearing off and dyskinesia
Wearing off is predictable return of symptoms before the next levodopa dose; dyskinesia is excessive involuntary movement, often at peak dose. First obtain a timed symptom/medicine diary. Check adherence, constipation/absorption issues and interacting dopamine blockers. Adjusting dose interval, formulation or adding an adjunct must be specialist-guided; simply escalating every dose can worsen dyskinesia and hallucinations.
4. Safety and OSCE
Ask about falls, BP lying/standing, swallowing, constipation, urinary symptoms, sleep attacks, hallucinations, cognition and impulse-control behaviour. Review all antiemetics/antipsychotics: dopamine-blocking medicines may worsen Parkinsonism. Counsel the patient and family to seek help for sudden confusion, dangerous sleepiness, compulsive behaviour, severe vomiting or inability to take regular dopaminergic medicine.
