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# Pacitane (Trihexyphenidyl)
## Overview
Trihexyphenidyl is an antimuscarinic (anticholinergic) agent used to manage parkinsonism and extrapyramidal symptoms. It acts by blocking central cholinergic receptors to restore the balance between dopamine and acetylcholine.
## Primary Indications
* Adjunctive therapy in Parkinson’s disease.
* Control of drug-induced extrapyramidal disorders (e.g., antipsychotic-induced parkinsonism).
## Adult Dosing
* **Parkinson’s Disease:** Initial 1 mg orally on day 1; increase by 2 mg every 3–5 days until a total of 6–10 mg daily (divided TID-QID) is reached.
* **Drug-Induced Extrapyramidal Disorders:** 1 mg initially; may increase as needed. Usual maintenance: 5–15 mg daily in divided doses.
* **Maximum Dose:** Generally 15 mg daily, though some sources suggest up to 20 mg in extreme clinical cases under strict supervision.
## Pediatric Dosing
* **Safety/Efficacy:** Not well-established. If used for drug-induced dystonia, common expert opinion suggests 1–2 mg total daily dose, titrated cautiously. Use in children should be restricted to specialist neurologists.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No formal standardized dosing guidelines exist. Use caution and lower starting doses, as reduced clearance may exacerbate anticholinergic toxicity.
* **Geriatric Patients:** High risk for BEERS Criteria adverse events (confusion, urinary retention, falls). Start at lowest possible dose (e.g., 0.5 mg) and titrate very slowly.
## Contraindications
* Hypersensitivity to the drug.
* Narrow-angle glaucoma.
* Pyloric or duodenal obstruction, stenosing peptic ulcers.
* Acalasia or bladder neck obstruction.
* Myasthenia gravis (relative).
## Adverse Effects
* **Common:** Dry mouth, blurred vision, constipation, nausea, tachycardia, dizziness.
* **Severe:** Confusion/delirium (especially in elderly), urinary retention, elevated intraocular pressure, hyperthermia, heat stroke (due to reduced sweating).
## Key Drug Interactions
* **Anticholinergics:** Additive toxicity with antihistamines, TCAs, and phenothiazines.
* **Dopaminergic agents:** May antagonize the effects of metoclopramide or dopamine agonists.
* **Absorption:** Reduced efficacy if taken with antacids or adsorbing agents.
## Monitoring
* Baseline and periodic intraocular pressure testing.
* Regular monitoring for cognitive impairment, confusion, or psychosis.
* Assessment of urinary output and GI motility.
## Clinical Pearls
* **Tapering:** Always discontinue gradually to avoid exacerbating parkinsonian or extrapyramidal symptoms.
* **Administration:** Can be taken with food to minimize GI upset.
* **Anticholinergic Burden:** Systematically review the patient's total anticholinergic load; avoid polypharmacy with other agents like benztropine or diphenhydramine.
* **Cognition:** Trihexyphenidyl should generally be avoided in patients with pre-existing dementia due to the risk of "anticholinergic-induced delirium."
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*Disclaimer: This information is for educational purposes and does not replace professional clinical judgment. Always verify current prescribing information, institutional protocols, and specific patient contraindications via reliable primary resources (e.g., Lexicomp, UpToDate) before prescribing or administering medication.*
