Are high doses of carbidopa a concern - A randomized, clinical trial in Parkinsons disease

Movement Disorders, 05/10/2012

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.


  • The authors 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.
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