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# Pacitane (trihexyphenidyl)
## Overview
Trihexyphenidyl is a synthetic tertiary amine antispasmodic drug that acts as a muscarinic acetylcholine receptor antagonist. It is used primarily for its central anticholinergic effects to treat Parkinsonism and extrapyramidal symptoms.
## Primary Indications
* Adjunctive treatment of all forms of Parkinsonism (postencephalitic, arteriosclerotic, and idiopathic).
* Control of drug-induced extrapyramidal disorders (secondary to neuroleptics).
## Adult Dosing
* **Parkinsonism:** Initial dose is 1 mg orally on day one. Increase by 2 mg increments at intervals of 3–5 days until a total of 6–10 mg/day is reached.
* **Drug-induced Extrapyramidal Symptoms:** 1 mg daily. May increase to a total of 5–15 mg daily if needed.
* **Maximum Dose:** Generally 15 mg/day.
## Pediatric Dosing
Safety and efficacy in children have not been formally established. Use is generally avoided due to high sensitivity to anticholinergic side effects. If required for refractory dystonia, clinical practice often starts at 0.05–0.1 mg/kg/day in divided doses, titrated cautiously. **Local institutional protocols must be consulted.**
## Dose Adjustments
* **Geriatric Patients:** High risk of confusion, urinary retention, and falls. Start at the lowest possible dose (e.g., 0.5–1 mg daily) and titrate slowly. Avoid if possible (Beers Criteria).
* **Hepatic/Renal Impairment:** No specific guidelines; use with caution and adjust downward if systemic accumulation is suspected.
## Contraindications
* Hypersensitivity to trihexyphenidyl.
* Narrow-angle glaucoma.
* Pyloric or duodenal obstruction, or stenosing peptic ulcers.
* Prostatic hypertrophy or bladder neck obstruction.
* Myasthenia gravis.
* Tachycardia/arrhythmias.
## Adverse Effects
* **Common:** Dry mouth, blurred vision, dizziness, nervousness, constipation, urinary hesitancy, and tachycardia.
* **Serious:** Glaucoma, urinary retention, hallucinations, confusion/delirium (especially in elderly), and risk of heatstroke (impaired sweating).
## Key Drug Interactions
* **Other Anticholinergics:** Additive toxicity (e.g., antihistamines, TCAs).
* **Oral Levodopa:** Trihexyphenidyl may reduce levodopa absorption by delaying gastric emptying.
* **CNS Depressants:** May potentiate sedation when combined with alcohol, opioids, or benzodiazepines.
* **Haloperidol/Phenothiazines:** May decrease efficacy of these antipsychotics due to opposing pharmacological actions.
## Monitoring
* Baseline and periodic intraocular pressure measurements.
* Monitoring for urinary retention and bowel function.
* Assess mental status, particularly in older adults (risk of anticholinergic delirium).
* Gradual withdrawal (to prevent recurrence of extrapyramidal symptoms).
## Clinical Pearls
* **Administration:** Can be taken with or after meals to reduce gastric irritation.
* **Abuse Potential:** Has been associated with reports of misuse for euphoric/hallucinogenic effects.
* **Heat Sensitivity:** Advise patients to avoid vigorous exercise or exposure to hot weather, as the drug impairs the body's ability to dissipate heat through perspiration.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice varies by jurisdiction and institution. Always verify specific dosing, safety warnings, and contraindications via official product labeling or current local clinical guidelines prior to prescribing or administering medication.
