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# Pacitane (Trihexyphenidyl)
## Overview
Trihexyphenidyl is an antispasmodic agent and a synthetic anticholinergic. It acts primarily by blocking central cholinergic receptors to restore the balance between dopamine and acetylcholine in the basal ganglia.
## Primary Indications
* Adjunctive therapy in all forms of Parkinson’s disease (postencephalitic, arteriosclerotic, and idiopathic).
* Control of extrapyramidal disorders induced by CNS drugs (e.g., antipsychotics).
## Adult Dosing
* **Parkinson’s Disease:** Initial dose 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 Disorders:** Initial dose 1 mg/day. May increase gradually based on response. Usual maintenance range is 5–15 mg/day in divided doses.
* **Maximum Dose:** Generally 15 mg/day, though some clinicians may use higher under strict supervision.
## Pediatric Dosing
* **Drug-Induced Extrapyramidal Disorders:** Safety and efficacy are not well-established. Use is clinical-judgement based. Limited data suggest 1–2 mg/day in divided doses, titrated cautiously. Consultation with a pediatric neurologist is strongly advised.
## Dose Adjustments
* **Renal/Hepatic Impairment:** Use with caution. No standardized dosage adjustments exist; start at the lower end of the dosing range due to potential for accumulation and increased sensitivity to anticholinergic effects.
* **Elderly:** Highly susceptible to adverse CNS effects (confusion, delirium). Start at 1 mg/day and titrate very slowly.
## Contraindications
* Hypersensitivity to the drug.
* Narrow-angle glaucoma.
* Pyloric or duodenal obstruction, or stenosing peptic ulcers.
* Prostatic hypertrophy or bladder neck obstruction.
* Myasthenia gravis.
## Adverse Effects
* **Common:** Dry mouth, blurred vision, dizziness, nervousness, constipation, urinary retention, and tachycardia.
* **Serious:** Psychosis, confusion, hallucinations (especially in the elderly), angle-closure glaucoma, and heat stroke (decreased sweating).
## Key Drug Interactions
* **Anticholinergics:** Additive toxicity (e.g., diphenhydramine, benztropine, TCAs).
* **Antipsychotics:** May decrease the efficacy of antipsychotics or exacerbate antipsychotic-induced tardive dyskinesia.
* **Alcohol:** Increased CNS depression and cognitive impairment.
## Monitoring
* Monitor for cognitive changes, memory impairment, and signs of psychotic behavior.
* Monitor intraocular pressure if clinical signs of glaucoma appear.
* Monitor bowel and bladder function (esp. in geriatric patients).
## Clinical Pearls
* Administering after meals may reduce minor GI side effects; administering before meals may be preferred if dry mouth is not a significant issue.
* Avoid abrupt withdrawal; taper the dose gradually to prevent precipitation of severe extrapyramidal symptoms.
* High risk for "Beers Criteria" concerns in patients age 65+ due to significant anticholinergic burden.
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**Educational Disclaimer:** This information is for educational purposes only. Always verify current prescribing information, local hospital protocols, and patient-specific contraindications via official sources (e.g., FDA-approved labeling, Lexicomp, or Micromedex) before prescribing or administering medication.
