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Parkinson's disease - Management
How are levodopa and dopa-decarboxylase inhibitors used in secondary care?

Levodopa

  • Is a precursor of dopamine and is metabolized centrally and peripherally by dopa-decarboxylase, catechol-O-methyltransferase (COMT), and monoamine oxidase.
  • Over time, the response may decrease and motor complications may occur, including:
    • Motor fluctuations, such as unpredictable switching between 'on' and 'off' states (on-off phenomenon), wearing off between doses, and dose failures.
    • Dyskinesias, such as athetosis (slow, writhing motions of fingers and hands) and dystonia (involuntary spasms of muscle contraction that cause abnormal movements and postures) occur.
  • Modified-release levodopa preparations may be used to reduce motor complications in people with later Parkinson's disease but can increase 'off' time and are not the drugs of first choice.
  • Oral dispersible levodopa may also be used to treat motor complications.
  • A levodopa gel given by continuous infusion directly into the jejunum (Duodopa®) is also licensed for the management of severe motor complications. It may reduce off-periods and improve motor function, activities of daily living, and quality of life, but its use may be limited by cost and the need for a jejunostomy.

Dopa-decarboxylase inhibitors (benserazide and carbidopa)

  • Are given routinely with levodopa (as co-beneldopa or co-careldopa) to prevent its peripheral metabolism to dopamine; this reduces its peripheral adverse effects and increases the amount of levodopa available to cross the blood–brain barrier.

[American Medical Directors Association, 2002; National Collaborating Centre for Chronic Conditions, 2006]

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