4.9.2 Antimuscarinic drugs used in parkinsonism

ChoiceDrugDosage
1st choicesProcyclidine 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

Prescribing Notes

  • 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.

Cautions

  • 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.