4.9.2 Antimuscarinic drugs used in parkinsonism

Choice	Drug	Dosage
1st choices	Procyclidine tablets 5mg	Dose: 2.5mg three times daily, increased gradually in steps of 2.5-5mg daily every 2-3 days if necessary; usual max 30mg daily in 2-4 divided doses; elderly preferably lower end of range
		Or
		Trihexyphenidyl hydrochloride tablets 2mg, 5mg	Dose: 1mg daily, increased by 2mg every 3-5 days according to response; usual maintenance dose 5-15mg daily in 3-4 divided doses (max 20mg daily); elderly preferably lower end of range – see cautions

Antimuscarinics are sometimes used as a first line therapy in young onset Parkinson’s Disease under specialist supervision, but not generally recommended in older patients – see Cautions
Antimuscarinics may occasionally be useful in patients with tremor which is unresponsive to other drugs, on the advice of a specialist.
Tardive dyskinesia is not improved by antimuscarinic drugs and may be made worse.

Antimuscarinics may cause cognitive impairment and urinary retention. They should be avoided in older patients.
Antimuscarinics are not generally recommended for use in Parkinson’s Disease because of toxicity in the elderly and the risk of aggravating dementia.
Abrupt withdrawal of antimuscarinics should be avoided.