Procyclidine

Procyclidine hydrochloride is a centrally acting antimuscarinic drug used to reduce cholinergic overactivity in the basal ganglia. It provides symptomatic relief in Parkinson’s disease and drug-induced extrapyramidal syndromes (EPS), especially dystonia and rigidity. It remains a first-line option for acute dystonic reactions due to antipsychotic drugs. Always 🔗 check the BNF entry here for up-to-date dosing and cautions.

⚙️ Mode of Action

• Acts as a centrally acting competitive antimuscarinic agent at M₁ receptors in the brain.
• Restores the balance between dopaminergic inhibition and cholinergic excitation in the basal ganglia.
• By reducing cholinergic tone, it decreases rigidity, tremor, and dystonia in Parkinsonism and EPS.
• Has mild antihistaminic and local anaesthetic properties, contributing to its sedative effects.

💊 Indications & Dose

• Parkinson’s disease or drug-induced EPS:
  • Start 2.5 mg three times daily; increase gradually according to response up to a usual maximum of 30 mg/day.
  • In older adults, use half the dose due to increased risk of confusion, urinary retention, and falls.
• Acute dystonic reaction:
  • Procyclidine 5–10 mg IV or IM — onset within 10 minutes; repeat if symptoms recur.
  • Transition to oral maintenance therapy (2.5–5 mg TDS) if further episodes expected.

🧪 Pharmacology

• Onset: Oral: 1 hour; IV/IM: within 5–10 minutes.
• Half-life: ~12 hours.
• Metabolism: Hepatic (extensive first-pass metabolism).
• Excretion: Renal.

🤝 Interactions

• Other antimuscarinics (e.g. tricyclics, antihistamines): additive CNS and peripheral anticholinergic effects.
• Antipsychotics: may mask or worsen tardive dyskinesia; use only for EPS, not long-term prophylaxis.
• Alcohol, opioids, sedatives: increased drowsiness and impaired coordination.
• Antihypertensives: may enhance postural hypotension, especially in elderly patients.

⚠️ Cautions

• Cardiac disease or hypertension: risk of tachycardia and palpitations.
• Angle-closure glaucoma: may precipitate acute rise in intraocular pressure.
• Prostatic hypertrophy: risk of urinary retention.
• Hepatic or renal impairment: start at lower doses and titrate slowly.
• Avoid abrupt withdrawal — may cause rebound Parkinsonism or dystonia.

⛔ Contraindications

• Myasthenia gravis (worsens neuromuscular weakness).
• Intestinal obstruction or paralytic ileus.
• Untreated narrow-angle glaucoma.

💢 Side Effects

• CNS: drowsiness, dizziness, confusion, agitation, hallucinations (especially in elderly).
• Autonomic: dry mouth, blurred vision, constipation, urinary retention, tachycardia.
• Ocular: precipitate or worsen angle-closure glaucoma — advise prompt attention for eye pain or visual changes.
• Gastrointestinal: nausea, vomiting, reduced GI motility.

🧠 Clinical Pearls

• Useful for acute dystonic reactions from haloperidol, metoclopramide, or prochlorperazine — rapid and reliable relief.
• In idiopathic Parkinson’s disease, benefit is mainly for tremor rather than rigidity or bradykinesia.
• Avoid chronic use in elderly or those with cognitive impairment — high risk of confusion and falls.
• Always review need for continuation after acute episode; most drug-induced dystonias do not require ongoing therapy.
• Encourage hydration and monitor for urinary difficulty and constipation.

📚 References

• BNF: Procyclidine Hydrochloride
• NICE CKS: Parkinson’s disease – management and adverse effect treatment.
• UpToDate: “Acute dystonic reactions to antipsychotics and antiemetics.”
• MHRA Drug Safety Update (2023): Anticholinergic burden in elderly patients.