Trihexyphenidyl hydrochloride

How it works

It blocks central muscarinic acetylcholine receptors, helping to restore the dopamine-acetylcholine balance in the basal ganglia.

Prescribing in practice

• Antimuscarinic adverse effects and confusion are common, so it should be avoided or used very cautiously in older or cognitively impaired patients in whom it can precipitate delirium.
• It is contraindicated or hazardous in narrow-angle glaucoma, significant urinary retention, prostatic enlargement and gastrointestinal obstruction.
• It should not be withdrawn abruptly, and additive effects occur with other anticholinergic drugs.

Monitoring

Monitor cognition, mood, intraocular and urinary symptoms, and motor response during treatment.

Counselling the patient

• Report dry mouth, blurred vision, difficulty passing urine, constipation or confusion.
• Avoid stopping the medicine suddenly.
• Be cautious with other medicines that cause dry mouth or drowsiness.

Evidence & guidelines

Antimuscarinics such as trihexyphenidyl have a long-established but limited role in Parkinson's disease, mainly for tremor, as reflected in standard guidance.