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Antimuscarinic Drugs for Parkinson's

Drugs in this group include benzatropine, orphenadrine, procyclidine, trihexyphenidyl (formerly benzhexol), amantidine. They work by reducing the effects of central cholinergic excess caused by lack of dopamine.

Indications1,2,3
  • They are effective in improving motor function but neuropsychiatric and cognitive adverse events occur frequently and are a more common reason for withdrawal than lack of efficacy.
  • They are useful in drug-induced Parkinson's, but they are not used in idiopathic condition as less effective than dopaminergic drugs and are associated with cognitive impairment.
  • They may have beneficial effects on tremor in some people.
  • They are useful in reducing sialorrhoea, but have no beneficial effect on tardive dyskinesia, and may make it worse.
  • Amantadine can be used as monotherapy in early Parkinson's Disease (PD) (for tremor or bradykinesia) but it has a weak and short-lived benefit. The evidence-base confirming efficacy and safety is lacking.

Contraindications1

Tardive dyskinesia.

Cautions1,4,5,6,7,8

  • Cardiovascular disease
  • Angle-closure glaucoma - can cause blurred vision
  • Gastro-intestinal obstruction
  • Prostatic hypertrophy - can aggravate hypertrophy and cause urinary retention
  • Elderly - confusion, hallucinations, memory impairment.
  • Can affect performance of skilled tasks, e.g. driving
  • Avoid sudden withdrawal - can cause confusion and recurrence of original symptoms
  • Potential for abuse - can cause alteration of mental function, hallucinations, delirium
  • Hepatic impairment, renal impairment - reduced metabolism and excretion likely to increase adverse effects
  • Pregnancy - lack of information
  • Lactation

Common Problems1,4,5

  • Dry mouth and blurred vision are common.
  • Confusion, hallucinations, euphoria, agitation, paranoid delusions, restlessness and memory impairment are particularly common in the elderly, but may also occur in younger individuals.
  • Less commonly nausea, vomiting and urine retention can occur.

Initiation1,4,5

Increase gradually, use lower end of dosage range for older patients.

Monitoring

None required.

Document references
  1. British National Formulary British Medical Association and Royal Pharmaceutical Society of Great Britain. London.
  2. Katzenschlager R, Sampaio C, Costa J et al Anticholinergics for symptomatic management of Parkinsons disease The Cochrane Database of Systematic Reviews 2002, Issue 3. Art. No.: CD003735.
  3. Crosby N J, K H O Deane, C E Clarke. Amantadine for dyskinesia in Parkinson's disease. The Cochrane Database of Systematic Reviews 2003, Issue 2. Art. No.: CD003467.
  4. Goetz, C.G., Koller, W.C., Poewe, W., et al. Anticholinergic therapies in the treatment of Parkinson''s disease. Movement Disorders 2002;17(Suppl. 4);S7-S12.
  5. Parkinson's disease, Clinical Knowledge Summaries (2007)
  6. Thompson F, Muir A, Stirton J et al Parksinon'as Disease Pharmaceutical Journal 2001:267;600-612
  7. Nappo SA, de Oliveira LG, Sanchez ZM, et al; Trihexyphenidyl (Artane): a Brazilian study of its abuse.; Subst Use Misuse. 2005;40(4):473-82. [abstract]
  8. Brocks DR; Anticholinergic drugs used in Parkinson's disease: An overlooked class of drugs from a pharmacokinetic perspective.; J Pharm Pharm Sci. 1999 May-Aug;2(2):39-46. [abstract]
AcknowledgementsEMIS is grateful to Dr Laurence Knott for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 265
Document Version: 1
DocRef: bgp25034
Last Updated: 17 Oct 2007
Review Date: 16 Oct 2008

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