Procyclidine

Why this drug is interesting

An acute dystonic reaction is one of the few things in emergency medicine you can abolish while the relatives watch. A young patient given metoclopramide, prochlorperazine or an antipsychotic develops torticollis, trismus, tongue protrusion or an oculogyric crisis; they are frightened, often unable to speak clearly, and frequently misdiagnosed as having a seizure, a psychiatric episode or tetanus. An anticholinergic reverses it within minutes.

The reason this page exists is that the formulation which made that possible has gone.

Pharmacology

Mechanism

The nigrostriatal pathway holds dopaminergic and cholinergic activity in balance. Dopamine D₂ blockade — by antipsychotics, by metoclopramide, by prochlorperazine — leaves striatal cholinergic transmission relatively unopposed, and the result is the extrapyramidal syndromes. Procyclidine is an antimuscarinic that reduces that cholinergic activity and restores the balance.

This is why the reversal is so fast: nothing has to be metabolised or eliminated, and no receptor has to be vacated by the offending drug. The antagonist simply rebalances the circuit while the D₂ blocker is still present.

Pharmacokinetics

The mean plasma elimination half-life is long enough that twice daily oral administration is adequate if more convenient than three times daily, and oral dosing may be better tolerated with food.¹

Dosing

Neuroleptic-induced extrapyramidal symptoms — the licensed oral regimen

"Treatment is usually initiated at 2.5 mg procyclidine three times per day, increasing by 2.5 mg daily until symptoms are relieved. The effective maintenance dose is usually 10 to 30 mg procyclidine per day."¹

The former injection

For completeness, and because it remains in circulating protocols: procyclidine injection was 5 mg/mL, and the conventional dose for acute dystonia was 5–10 mg intramuscularly or intravenously as a single dose, repeatable. That product is no longer supplied, its SmPC is not on the emc, and this figure is recorded here as history rather than as a prescribable dose.

Parkinson's disease

Start at 2.5 mg three times daily, increasing by 2.5–5 mg per day every two to three days; usual maintenance 15–30 mg daily, with doses up to 60 mg well tolerated at the prescriber's discretion.¹

Duration and review

After 3 to 4 months of therapy, procyclidine should be withdrawn and the patient observed to see whether the neuroleptic-induced symptoms recur; if they do, it is reintroduced. Periodic cessation is recommended even in patients who appear to need it long term.¹ Anticholinergics accumulate cognitive and antimuscarinic burden, and indefinite prescription without review is the commonest error after discharge.

Special populations

• Children — "the use of Kemadrin in this age group is not recommended".¹ Acute dystonia is nonetheless common in children and adolescents given antiemetics, so this is a real gap requiring specialist advice.
• Older people — may be more susceptible to anticholinergic effects; a reduced dose may be required.¹

The supply problem, and what is left

The clinical situation the injection existed for is a patient with trismus, tongue protrusion or laryngeal involvement who cannot reliably swallow a tablet. Options now, none of them clean:

Oral procyclidine

Practical, and the sensible default if the patient can swallow.³ Tablets are 5 mg; oral solutions at 2.5 mg/5 mL and 5 mg/5 mL exist and may be easier with a dystonic tongue.¹

Benzatropine injection

Reported as the recommended injectable alternative at 1–2 mg IM or IV, but "only available in the UK as an unlicensed import, requiring patient-named ordering, with longer lead times".³ That is not a resuscitation-room drug unless your pharmacy already stocks it.

A parenteral antihistamine

First-generation antihistamines have antimuscarinic activity and are used for this indication in other health systems. In the UK this is off-label and should be discussed with the poisons service or pharmacy rather than improvised.

A benzodiazepine

See midazolam. Not a mechanistic treatment for dystonia, but it relieves distress and muscle spasm while a definitive drug is found, and it is universally available.

Antipsychotic overdose

Procyclidine's antidotal role extends into deliberate antipsychotic poisoning, where extrapyramidal reactions can be severe. Haloperidol's label recommends parenteral administration of an anticholinergic antiparkinsonian agent for severe extrapyramidal reactions — which is now difficult to comply with in the UK.

Note the direction of travel: procyclidine treats the movement disorder, not the poisoning. It has no effect on sedation, hypotension, QT prolongation or the sodium channel.

Safety

Antimuscarinic burden

The predictable effects are dry mouth, blurred vision, urinary retention, constipation, tachycardia and confusion — the last particularly in older people, in whom a reduced dose is advised.¹ In a patient already on an antipsychotic with antimuscarinic activity, procyclidine adds to an existing load.

Misuse

Cautions

Standard antimuscarinic cautions apply — angle-closure glaucoma, prostatic hypertrophy and gastrointestinal obstruction — and the drug should not be stopped abruptly after prolonged use. As above, tardive dyskinesia may be worsened by anticholinergics.

Critical appraisal

There is no randomised evidence that procyclidine reverses acute dystonia, and there does not need to be: the effect is rapid, obvious, reproducible and mechanistically transparent, and the condition is otherwise distressing and prolonged. This is one of the small number of treatments where clinical experience is genuinely sufficient.

The interesting problem is entirely one of supply. A cheap, effective, decades-old injection has been withdrawn for commercial rather than safety reasons, and its recommended replacement is an unlicensed import — a pattern this batch of monographs has now met repeatedly, on the pralidoxime, pyridoxine and levocarnitine pages. Cheap parenteral antidotes for uncommon emergencies are exactly the products a market does not reliably supply.

References

1. 1
   Kemadrin Tablets 5 mg (procyclidine hydrochloride) — Summary of Product Characteristics, Aspen. electronic Medicines Compendium, product 5460. Sections 4.1, 4.2. Source of the licensed indications including acute dystonic reactions and akathisia, the 2.5 mg three times daily start, the 10–30 mg daily maintenance for extrapyramidal symptoms, the 15–30 mg and 60 mg Parkinson's figures, the 3–4 month review, the paediatric and elderly statements and the twice-daily half-life note. Verified 4 September 2026.
2. 2
   Medicines containing procyclidine hydrochloride — electronic Medicines Compendium ingredient index 627. Checked 4 September 2026: five products listed — Kemadrin Tablets 5 mg (5460), Procyclidine Hydrochloride 5 mg tablets (8488), Procyclidine Tablets 5 mg (14456), and Procyclidine Rosemont oral solutions 2.5 mg/5 mL (1562) and 5 mg/5 mL (1563). All oral; no injection is listed.
3. 3
   Ashtons. Discontinuation of procyclidine injection and management of acute dystonia, 8 May 2026. ashtons.com. Source of the discontinuation, the benzatropine 1–2 mg IM/IV unlicensed-import alternative and the recommendation that services review protocols. A pharmacy advisory notice; it cites no official regulatory notification, and none was located independently.