Anticholinergic — Parkinson's Disease / Dystonia Pregnancy: US Pregnancy Category C — should be given to a pregnant woman only if clearly needed; animal reproduction studies not conducted

Trihexyphenidyl

Brand names: Broflex

Trihexyphenidyl is an antimuscarinic (anticholinergic) agent used in Parkinson's disease, particularly for tremor, and to manage drug-induced extrapyramidal symptoms.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Idiopathic parkinsonism (initial therapy): 1 mg on the first day, then increase by 2 mg increments at intervals of 3 to 5 days until a total of 6 to 10 mg is given daily (optimal total individualised)

Route: Oral

Frequency: Total daily dose best divided into 3 doses taken at mealtimes; high doses (>10 mg daily) may be divided into 4 parts (3 at mealtimes, the fourth at bedtime)

Dosage should be individualised; start low and increase gradually, especially in patients over 60. Some patients, chiefly the postencephalitic group, may require a total daily dose of 12 to 15 mg. Drug-induced parkinsonism: total daily dosage usually 5 to 15 mg (occasionally controlled with as little as 1 mg daily); it may be advisable to commence with a single 1 mg dose and increase subsequent doses until control is achieved. Concomitant use with levodopa: a trihexyphenidyl dose of 3 to 6 mg daily in divided doses is usually adequate, and the usual dose of each drug may need to be reduced. Avoid abrupt withdrawal (risk of acute exacerbation of parkinsonism and neuroleptic malignant syndrome). Paediatric use: safety and effectiveness in paediatric patients have not been established.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to trihexyphenidyl or to any of the other ingredients
Narrow angle glaucoma (blindness after long-term use due to narrow angle glaucoma has been reported)

Side effects

Dryness of the mouth
Blurred vision
Dizziness
Mild nausea
Nervousness (minor side effects experienced by 30 to 50 percent of patients)

Interactions

Alcohol or other CNS depressants — may cause increased sedative effects
Cannabinoids, barbiturates, opiates and alcohol — additive effects; abuse potential exists
Monoamine oxidase inhibitors and tricyclic antidepressants with anticholinergic activity — may intensify anticholinergic effects
Levodopa — usual dose of either drug may need to be reduced during concomitant therapy (may increase drug-induced involuntary movements)

Clinical monograph

How it works

It blocks central muscarinic acetylcholine receptors, helping to redress the relative cholinergic excess that results from dopamine deficiency or dopamine-receptor blockade in the basal ganglia.

Prescribing in practice

Antimuscarinic effects make it hazardous in the elderly and it should be avoided where there is cognitive impairment, narrow-angle glaucoma, urinary retention or significant prostatic enlargement.
Confusion, hallucinations, dry mouth, blurred vision and constipation are common, especially in older patients.
It should be withdrawn gradually rather than stopped abruptly.

Monitoring

Monitor cognition, intraocular pressure where relevant, bowel and bladder function and overall antimuscarinic burden.

Counselling the patient

Report confusion, hallucinations, eye pain or difficulty passing urine.
Dry mouth and blurred vision are common; take care with tasks needing clear vision.

Evidence & guidelines

Its role in Parkinsonian tremor and drug-induced extrapyramidal symptoms is long established in clinical practice and standard references.

Reference: NICE NG71 (Parkinson's Disease); British Paediatric Neurology Association Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways