Side effects of the antiparkinsonian drugs
1. Big picture
Antiparkinsonian drugs improve dopamine deficiency in Parkinson’s disease, but because dopamine also affects the psyche, autonomic system, sleep-wake regulation, gastrointestinal tract and movement control, these drugs commonly cause side effects.
The key exam sentence:
Antiparkinsonian drugs commonly cause drowsiness, sleep attacks, nightmares, hallucinations, agitation, orthostatic hypotension, nausea, vomiting, constipation, leg edema and drug-induced dyskinesias.
The most important clinical trap:
Treating Parkinson’s psychosis with haloperidol worsens parkinsonism. Use Parkinson-safe antipsychotics such as quetiapine or clozapine when needed.
2. Main antiparkinsonian drug groups
| Drug group | Examples | Main role |
|---|---|---|
| Levodopa + dopa decarboxylase inhibitor | levodopa/carbidopa, levodopa/benserazide | strongest symptomatic treatment |
| Dopamine agonists | pramipexole, ropinirole, rotigotine, apomorphine, bromocriptine | stimulate dopamine receptors |
| MAO-B inhibitors | selegiline, rasagiline, safinamide | reduce dopamine breakdown |
| COMT inhibitors | entacapone, tolcapone, opicapone | prolong levodopa effect |
| Amantadine | oral or IV | dyskinesia, sometimes crisis support |
| Anticholinergics | biperiden, procyclidine, trihexyphenidyl, metixene | tremor-dominant disease, mainly younger patients |
| Advanced therapies | levodopa intestinal gel, apomorphine infusion, deep brain stimulation |
MAO-B = monoamine oxidase B. COMT = catechol-O-methyltransferase.
3. General side effects of antiparkinsonian drugs
Lecture list of common side effects:
- dullness;
- drowsiness;
- daytime sleep attacks;
- sleep disorders;
- nightmares;
- hallucinations;
- orthostatic hypotension;
- nausea;
- vomiting;
- constipation;
- symmetrical leg edema not responding to diuretics.
Additional important effects:
- confusion;
- agitation;
- impulse-control disorders;
- dyskinesias;
- motor fluctuations;
- psychosis;
- urinary retention with anticholinergics;
- dry mouth;
- tachycardia;
- cognitive worsening in elderly patients.
4. Levodopa side effects
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