Clinical Overview
Trihexyphenidyl is an anticholinergic medication indicated for Parkinson’s disease and drug-induced extrapyramidal symptoms. It is commonly used to treat extrapyramidal side effects caused by antipsychotic medications, including dystonia, parkinsonism, and akathisia. It helps restore the balance between dopamine and acetylcholine in the basal ganglia.
Primary Clinical Applications
Trihexyphenidyl is indicated for Parkinson’s disease and drug-induced extrapyramidal reactions. It is frequently used as adjunctive therapy to treat movement disorders caused by antipsychotic medications, including acute dystonic reactions, drug-induced parkinsonism, and sometimes akathisia.
Mechanism and Clinical Benefits
Trihexyphenidyl blocks muscarinic acetylcholine receptors in the central nervous system, helping to restore the balance between dopamine and acetylcholine in the basal ganglia. This rebalancing alleviates the movement disorders that occur when dopamine activity is reduced or blocked by antipsychotic medications.
Clinical Considerations
While effective for extrapyramidal symptoms, trihexyphenidyl has significant anticholinergic side effects that can be problematic, particularly in elderly patients. It can cause cognitive impairment, confusion, and may worsen tardive dyskinesia. The medication should be used at the lowest effective dose and discontinued gradually when no longer needed.
Prescribing Information
Dosing & Administration
Parkinson’s Disease:
- Initial: 1 mg on first day
- Titration: Increase by 2 mg every 3-5 days until therapeutic response
- Range: 6-10 mg daily in 3-4 divided doses
- Maximum: 15 mg daily
Drug-Induced Extrapyramidal Symptoms:
- Initial: 1 mg daily
- Titration: Increase by 1-2 mg every few days as needed
- Range: 5-15 mg daily in divided doses
- Acute dystonia: 5-10 mg IM/IV, then oral maintenance
Administration:
- Divide daily dose into 3-4 administrations
- Take with or after meals to reduce GI upset
- Consistent timing each day
- Taper gradually when discontinuing
Indications
- Treatment of Parkinson’s disease
- Treatment of drug-induced extrapyramidal reactions
- Adjunctive therapy for movement disorders
Contraindications
- Hypersensitivity to trihexyphenidyl
- Narrow-angle glaucoma
- Bowel obstruction
- Megacolon
- Myasthenia gravis
Warnings & Precautions
- Anticholinergic effects: Dry mouth, constipation, urinary retention, confusion
- Cognitive impairment: Particularly problematic in elderly patients
- Heat stroke: Reduced sweating may lead to hyperthermia
- Tardive dyskinesia: May mask or worsen symptoms
- Abuse potential: Can cause euphoria and hallucinations at high doses
- Withdrawal: Abrupt discontinuation may worsen extrapyramidal symptoms
Drug Interactions
- Other anticholinergics: Additive anticholinergic effects
- CNS depressants: Enhanced sedation
- Phenothiazines: May reduce antipsychotic effectiveness
- Digoxin: May increase digoxin levels
- Levodopa: May reduce effectiveness
Adverse Reactions
Common (>10%):
- Dry mouth, blurred vision, constipation, nausea
- Dizziness, nervousness, drowsiness
Serious:
- Confusion, hallucinations, memory impairment
- Urinary retention, paralytic ileus
- Heat stroke, angle-closure glaucoma
Special Populations
- Elderly: Increased risk of confusion and cognitive impairment
- Glaucoma: Contraindicated in narrow-angle glaucoma
- Pregnancy: Category C – use only if benefits outweigh risks
- Hot weather: Monitor for heat stroke due to reduced sweating
Medical Disclaimer: This information is for educational purposes only and is not intended as medical advice. Always consult with qualified healthcare professionals before making any treatment decisions. Individual patient circumstances may vary significantly.
