Antimuscarinic drugs are less effective than levodopa for idiopathic Parkinson's disease. If they are used it is most commonly in the earlier stages of Parkinson's disease, with the aim of improving motor symptoms. Antimuscarinic drugs should not be offered to patients with Parkinson's disease who have developed dyskinesia or motor fluctuations. Tardive dyskinesia is not improved and may be worsened by antimuscarinic drugs.

Antimuscarinic drugs have value in post-encephalitic parkinsonism. They reduce tremor and rigidity but have little effect on bradykinesia. They are useful in reducing sialorrhoea and reducing the symptoms of drug-induced parkinsonism.

They also have a high incidence of peripheral parasympathomimetic side effects, and may also worsen confusional states.

Orphenadrine

• Oral solution sugar free 50mg/5ml (£139.59 = 150ml)

Indications

• Parkinsonism; drug-induced extrapyramidal symptoms (but not tardive dyskinesia)

Dose

• Adults: Initially 150 mg daily in divided doses, then increased in steps of 50 mg every 2–3 days, adjusted according to response; usual dose 150–300 mg daily in divided doses; maximum 400 mg per day
• Elderly: Preferably dose at lower end of range

Procyclidine

• Tablets 5mg (click here for preferred brand)
• Oral solution sugar free 2.5mg/5ml, 5mg/5ml (£70.04 = 5mg/5ml x 150ml)
• Solution for injection 10mg/2ml (£14.50 per ampoule)

Indications and dose

• Parkinsonism; drug-induced extrapyramidal symptoms (but not tardive dyskinesia)
  • By mouth: Adults: 2.5mg 3 times daily, increased gradually in steps of 2.5–5mg daily every 2–3 days if necessary; usual maximum 30mg daily in 2–4 divided doses (60mg daily in exceptional circumstances)
• Acute dystonia:
  • Intramuscular or intravenous injection: Adults: Acute dystonia, 5–10mg (occasionally more than 10mg), usually effective in 5–10 minutes but may need 30 minutes for relief

Notes

1. For elderly patients use lower end of dose range.
2. Where a preferred brand is recommended for a particular presentation, prescribing by brand helps ensure cost-efficient use of local NHS resources (see preferred brand link above).

Trihexyphenidyl

• Tablets 2mg, 5mg (£12.05 = 5mg x 84 tablets)
• Oral solution 5mg/5ml (£108.44 = 200ml)

Indications and dose

• Parkinsonism; drug-induced extrapyramidal symptoms (but not tardive dyskinesia)
  • By mouth: Adults: 1mg daily, increased by 2mg every 3–5 days according to response; usual maintenance dose 5–15mg daily in 3–4 divided doses (maximum 20mg daily). Elderly: lower end of range is preferable
• Parkinson's disease (if used in combination with co-careldopa or co-beneldopa
  • By mouth: Maintenance dose 2-6mg daily in divided doses

Notes

1. Not recommended for use in Parkinson's disease because of toxicity in the elderly and the risk of aggravating dementia.