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Anticholinergic — Parkinson's Disease / Dystonia Pregnancy: Use with caution — limited data; anticholinergic effects on fetus possible

Trihexyphenidyl

Brand names: Broflex

Adult dose

Dose: 1 mg on day 1; increase by 2 mg every 3–5 days
Route: Oral
Frequency: 3 times daily (with meals)
Max: 15 mg/day (Parkinson's); up to 30–40 mg/day in dystonia under specialist supervision
Slow titration essential to minimise anticholinergic side effects. Particularly useful for tremor-dominant Parkinson's in younger patients. Avoid in elderly — high risk of confusion and cognitive decline. Taper slowly on discontinuation.

Paediatric dose

Dose: 0.05–0.1 mg/kg/day initially mg/kg
Route: Oral
Frequency: 2–3 times daily
Max: Up to 40 mg/day in severe primary dystonia (specialist only)
Used in paediatric primary dystonia — higher doses tolerated than in adults; seek paediatric neurology guidance

Dose adjustments

Renal

Use with caution — reduce dose in significant renal impairment

Hepatic

Use with caution in hepatic impairment

Paediatric weight-based calculator

Used in paediatric primary dystonia — higher doses tolerated than in adults; seek paediatric neurology guidance

Clinical pearls

  • Generally avoided in elderly Parkinson's patients — anticholinergic burden causes cognitive decline and falls
  • More useful in younger patients with predominant tremor not responsive to levodopa
  • In primary dystonia (DYT1): high-dose trihexyphenidyl may be dramatically effective — up to 40 mg/day tolerated in children/young adults
  • Central anticholinergic effects can cause drug-induced psychosis — reduce dose or switch agent
  • Taper slowly over weeks/months to prevent cholinergic rebound

Contraindications

  • Narrow-angle glaucoma
  • Prostatic hypertrophy with urinary retention
  • GI obstruction
  • Myasthenia gravis
  • Tardive dyskinesia (may worsen)

Side effects

  • Dry mouth
  • Blurred vision
  • Constipation
  • Urinary retention
  • Confusion and hallucinations (especially elderly)
  • Tachycardia
  • Cognitive impairment
  • Anhidrosis
  • Hyperthermia in hot weather

Interactions

  • Additive anticholinergic effects with TCA, antihistamines, antipsychotics
  • Reduces gastric motility — delayed levodopa absorption
  • MAOIs — enhance anticholinergic effects

Monitoring

  • Cognitive assessments (especially elderly)
  • Intraocular pressure in glaucoma risk
  • Urinary symptoms
  • Core temperature in hot weather

Reference: BNFc; BNF 90; NICE NG71 (Parkinson's Disease); British Paediatric Neurology Association Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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