Phenergan (Promethazine) is Contraindicated in Parkinson's Disease
Promethazine should be avoided in patients with Parkinson's disease due to its dopamine receptor antagonist properties, which can worsen motor symptoms and cause extrapyramidal side effects. While not explicitly listed as an absolute contraindication in the provided evidence, promethazine's mechanism of action directly opposes the dopaminergic therapy that forms the foundation of Parkinson's disease treatment.
Mechanism of Harm
- Promethazine is a phenothiazine with dopamine receptor antagonist effects, along with antihistaminergic and anticholinergic properties 1
- Drugs that block dopamine receptors at the basal ganglionic level can induce or worsen parkinsonism, accounting for 4% of all patients with parkinsonism seen in neurology clinics 2
- The use of classical neuroleptic drugs and antidopaminergic agents in Parkinson's disease patients is contraindicated because of their extrapyramidal effects 3
Clinical Considerations
- Promethazine can cause extrapyramidal symptoms ranging from restlessness to oculogyric crises, in addition to hypotension, respiratory depression, and neuroleptic malignant syndrome 1
- The aged population is at increased risk of drug-induced parkinsonism due to intrinsic factors and polypharmacy 2
- Metoclopramide, another dopamine antagonist antiemetic, similarly blocks central dopamine receptors and worsens motor parkinsonian symptoms 4
Safer Alternatives for Nausea/Vomiting in Parkinson's Disease
- Ondansetron (5-HT3 receptor antagonist) is the preferred antiemetic, as it does not affect dopamine receptors 1
- Domperidone is a safer alternative because very little crosses the blood-brain barrier, resulting in minimal risk of extrapyramidal adverse effects 4
- Diphenhydramine (antihistamine) can be used for nausea, though it has anticholinergic effects that require caution in older adults 1
Common Pitfall
Physicians may inadvertently prescribe promethazine for nausea without recognizing its antidopaminergic properties and potential to exacerbate Parkinson's disease symptoms 2. Always review a patient's neurological history before prescribing any phenothiazine or dopamine antagonist medication.