Are high doses of carbidopa a concern? A randomized, clinical trial in Parkinson's disease

Lissa S. Brod, Jason L. Aldred, John G. Nutt

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Recommended doses of carbidopa are 75-200 mg/day. Higher doses could inhibit brain aromatic amino-acid decarboxylase and reduce clinical effects. We compared 4-week outpatient treatments with carbidopa (75 and 450 mg/day) administered with L-dopa on the subjects' normal schedule. After each treatment phase, subjects had two 2-hour L-dopa infusions. The first infusion examined the effects of carbidopa doses administered the preceding 4 weeks, and the second infusion determined the acute effects of the two dosages of carbidopa. The antiparkinsonian effects and L-dopa and carbidopa plasma concentrations were monitored during the infusions. Twelve subjects completed the study. Carbidopa concentrations were eight times higher after the high-carbidopa phase. Area under the curve (AUC) for clinical ratings did not differ for the four L-dopa infusions, although AUC for plasma L-dopa was modestly increased with 450 mg of carbidopa. Nine subjects reported that the high-carbidopa outpatient phase was associated with greater response to L-dopa. Doses of 450 mg/day of carbidopa did not reduce the responses to L-dopa infusion, extending the safe range of carbidopa to 450 mg/day.

Original languageEnglish (US)
Pages (from-to)750-753
Number of pages4
JournalMovement Disorders
Issue number6
StatePublished - May 2012


  • Carbidopa
  • L-dopa
  • Parkinson's disease

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology


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