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# Pacitane (Trihexyphenidyl)
## Overview
Trihexyphenidyl is an antispasmodic agent and a synthetic tertiary amine anticholinergic. It exerts its effects by blocking central cholinergic receptors, helping to balance the neurotransmitter imbalance between acetylcholine and dopamine in the basal ganglia.
## Primary Indications
* Adjunctive treatment of all forms of Parkinsonism (postencephalitic, arteriosclerotic, and idiopathic).
* Drug-induced extrapyramidal reactions (e.g., neuroleptic-induced parkinsonism).
## Adult Dosing
* **Parkinsonism:** Initially 1 mg orally on day one. Increase by 2 mg increments at intervals of 3–5 days until a total daily dose of 6–10 mg is reached.
* **Drug-induced Extrapyramidal Reactions:** Initially 1 mg per day. Dosage can be titrated upward until control is achieved, typically 5–15 mg daily.
* **Maximum Dosage:** Usually 15 mg daily; clinical monitoring is required for doses exceeding this limit.
## Pediatric Dosing
Safety and efficacy in pediatric patients are not well established. Use is generally restricted to treatment of drug-induced extrapyramidal reactions under specialist supervision.
* **Suggested starting dose:** 1 mg daily.
* **Titration:** Individualized based on response and tolerability.
## Dose Adjustments
* **Renal/Hepatic Impairment:** Use with caution. If impairment is significant, lower initial doses and slower titration are recommended due to altered metabolism/excretion.
* **Geriatric Patients:** High susceptibility to anticholinergic side effects (e.g., confusion, urinary retention). Start at 1 mg daily and increase cautiously. **Considered inappropriate in the elderly per Beers Criteria.**
## Contraindications
* Hypersensitivity to trihexyphenidyl or any product components.
* Narrow-angle glaucoma.
* Pyloric or duodenal obstruction, pylorospasm, or achalasia.
* Prostatic hypertrophy or bladder neck obstruction.
* Tachycardia/arrhythmias.
* Myasthenia gravis.
## Adverse Effects
* **Common:** Dry mouth, blurred vision, constipation, nausea, dizziness, nervousness, and urinary retention.
* **Serious:** Cognitive impairment (especially in the elderly), hallucinations, psychotic episodes, tachycardia, and elevated intraocular pressure.
## Key Drug Interactions
* **Anticholinergics/Antihistamines:** Additive anticholinergic effects (increased risk of delirium, urinary retention).
* **Phenothiazines/Haloperidol:** May decrease the efficacy of antipsychotics or worsen anticholinergic toxic syndrome.
* **Levodopa:** Rarely, trihexyphenidyl may reduce systemic bioavailability of levodopa due to slowed gastric emptying.
## Monitoring
* **Baseline:** Intraocular pressure (baseline), cognitive function.
* **Ongoing:** Monitor for symptomatic improvement of extrapyramidal symptoms, assess for early signs of cognitive decline, urinary retention, and constipation.
## Clinical Pearls
* **Administration:** May be taken with or after meals to minimize gastric irritation.
* **Abrupt Withdrawal:** Do not discontinue abruptly; taper gradually to prevent rebound parkinsonism or withdrawal symptoms.
* **Antimuscarinic Toxicity:** Be vigilant for the signs of overdose/toxicity: "Hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter."
* **Dosing Variations:** Individual response varies significantly; always adhere to institutional protocols for titration speed.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult the most current product monograph, clinical guidelines, and institutional policies before prescribing or administering medication. Confirm drug doses using reliable, localized sources.
