Pacitane%20%28trihexyphenidyl%29

# Pacitane (trihexyphenidyl) ## Overview Trihexyphenidyl is a centrally acting anticholinergic agent used to reduce cholinergic overactivity in the basal ganglia. It improves rigidity, tremor, and dystonia but has limited effect on bradykinesia. ## Primary Indications - Parkinson disease (adjunct to levodopa or as monotherapy in early/mild cases) - Drug-induced extrapyramidal symptoms (EPS) including acute dystonia, parkinsonism, akathisia - Idiopathic or secondary dystonia (off-label) ## Adult Dosing - **Parkinsonism**: Initiate 1 mg orally once or twice daily. Increase by 2 mg every 3–5 days; usual maintenance 5–15 mg/day in 3–4 divided doses. Maximum 20 mg/day. - **Drug-induced EPS**: 1 mg orally once daily, titrate to 5–15 mg/day in divided doses as needed. Maximum 20 mg/day. - Dosing must be individualized; use lowest effective dose. Titration protocols vary by institution. ## Pediatric Dosing *(Limited evidence; use is off-label)* - **Dystonia/EPS**: Start 0.5–1 mg orally once or twice daily. Increase by 0.5–1 mg every 3–5 days. Typical range 2–8 mg/day in 2–3 divided doses. Maximum 12 mg/day (or 0.5–0.75 mg/kg/day, not to exceed adult max). Use with caution; base on weight and tolerability. ## Dose Adjustments - **Elderly or frail patients**: Start at 1 mg/day, titrate slowly (increase by 1 mg every 5–7 days). Lower maintenance doses often sufficient. - **Renal/hepatic impairment**: No specific guidelines; use with caution due to anticholinergic accumulation risk. - **Concomitant CNS depressants**: Consider dose reduction as sedation may be additive. ## Contraindications - Narrow-angle glaucoma (absolute) - Untreated urinary retention, prostatic hypertrophy (relative – may worsen) - Myasthenia gravis - Severe hepatic or renal impairment (relative – lack of safety data) - Hypersensitivity to trihexyphenidyl or any component ## Adverse Effects - **Common**: Dry mouth, blurred vision, constipation, urinary hesitancy, nausea, dizziness, drowsiness, nervousness. - **Serious**: Confusion, hallucinations (especially in elderly), tachycardia, heat intolerance, paralytic ileus, glaucoma exacerbation, central anticholinergic syndrome (high doses or overdose). - Withdrawal: Sudden cessation may precipitate cholinergic rebound (sweating, bradycardia, GI upset); taper slowly. ## Key Drug Interactions - **Other anticholinergics** (e.g., benztropine, atropine, amantadine): Additive anticholinergic effects – increase toxicity risk. - **Cholinergic agents** (e.g., donepezil, rivastigmine): Antagonize therapeutic effects; use with caution. - **CNS depressants** (e.g., benzodiazepines, alcohol, opioids): Enhanced sedation and cognitive impairment. - **Antipsychotics (typical)** : May reduce antipsychotic absorption; monitor therapeutic effect. - **Digoxin**: Trihexyphenidyl may reduce digoxin absorption (variable). ## Monitoring - Assess for anticholinergic side effects (dry mouth, vision, urinary function) at each visit. - In elderly: monitor cognition, confusion, falls risk. - In glaucoma patients: ensure intraocular pressure controlled; measure if symptoms change. - Therapeutic effect on tremor, rigidity, or EPS – titrate to symptom control. ## Clinical Pearls - Use lowest effective dose; tolerance to side effects often develops over 1–2 weeks. - Sustained-release formulations available (not interchangeable mg-for-mg with immediate-release); adjust timing. - Can be given with or without food; antacids may impair absorption (separate by 1–2 hours). - Discontinue gradually over 1–2 weeks to avoid withdrawal symptoms. - In drug-induced EPS, try reducing antipsychotic dose first before adding trihexyphenidyl. --- **Disclaimer:** This information is for educational purposes and does not replace current prescribing guidelines. Always consult the latest product monograph or local formulary for verified dosing, contraindications, and safety updates.