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# Pacitane (Trihexyphenidyl)
## Overview
Trihexyphenidyl is an antispasmodic/anticholinergic agent that acts as a central muscarinic acetylcholine receptor antagonist. It is used primarily to manage symptoms of Parkinson’s disease and drug-induced extrapyramidal reactions.
## Primary Indications
* Adjunctive therapy in all forms of Parkinson’s disease.
* Control of extrapyramidal disorders induced by CNS drugs (e.g., antipsychotics).
* *Note: Not effective for tardive dyskinesia.*
## Adult Dosing
* **Parkinson’s Disease:** Initial 1 mg orally on day 1; increase by 2 mg increments at 3–5 day intervals. Usual maintenance: 6–10 mg/day in 3–4 divided doses. Maximum: 15 mg/day.
* **Drug-Induced Extrapyramidal Symptoms:** Initial 1 mg/day. May increase as needed up to 5–15 mg/day in divided doses.
## Pediatric Dosing
* **Safety/Efficacy:** Not well-established. Use is off-label and requires specialist supervision.
* **Dosing:** Reported ranges suggest 1–2 mg total daily dose, divided, titrated based on clinical response and tolerance. Pediatric patients are highly sensitive to anticholinergic side effects (e.g., hyperthermia, tachycardia).
## Dose Adjustments
* **Renal/Hepatic Impairment:** No standard guidelines; use caution and consider lower starting doses and slower titration due to systemic anticholinergic risk.
* **Elderly:** Use with extreme caution (Beers Criteria). Higher risk for confusion, urinary retention, and constipation. Start low, go slow.
## Contraindications
* Hypersensitivity to the drug.
* Narrow-angle glaucoma.
* Pyloric or duodenal obstruction or stenosing peptic ulcers.
* Prostatic hypertrophy/bladder neck obstruction.
* Myasthenia gravis.
* Megacolon.
## Adverse Effects
* **Common:** Dry mouth, blurred vision, tachycardia, constipation, urinary retention, dizziness, nervousness.
* **Serious:** Psychosis, confusion, hallucinations (especially in the elderly), angle-closure glaucoma, hyperthermia.
## Key Drug Interactions
* **Anticholinergics:** Additive toxicity (e.g., diphenhydramine, tricyclic antidepressants) increases risk of delirium and urinary retention.
* **Antipsychotics:** May decrease the efficacy of antipsychotics or exacerbate tardive dyskinesia.
* **CNS Depressants:** Enhanced sedation.
## Monitoring
* Monitor for neuropsychiatric monitoring (confusion/hallucinations), especially in elderly patients.
* Assess intraocular pressure if indicated.
* Monitor bowel habits and urinary output.
## Clinical Pearls
* **Administration:** May be taken with or after meals to minimize gastric irritation. If taking for drug-induced EPS, consider dose reduction or discontinuation if the patient remains stable on the antipsychotic.
* **Avoid Abrupt Withdrawal:** Can precipitate a crisis; taper dose slowly.
* **Heat Sensitivity:** Advise patients of reduced sweating, which increases the risk of heatstroke during physical exertion or high temperatures.
* **Dosing uncertainty:** Always consult your institution’s specific formulary or neurology guidelines, as titration schedules vary significantly between practitioners.
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*Disclaimer: This information is for educational purposes only. Clinical practice guidelines and local protocols vary. Please verify all dosages and contraindications against the current manufacturer’s prescribing information and your institutional pharmacy database before prescribing.*
