Pharmacotherapy Newsletter

Volume 1, Issue 19, 05/25/2009

Question

Why is carbidopa added to levodopa (i.e., L-Dopa; Sinemet®; Sinemet CR®) for the treatment of Parkinson's disease, if when used alone has no therapeutic benefit?

Answer

Patients with Parkinson's disease are known to have a deficiency of dopamine in the brain.¹  In particular, the dopaminergic neurons within the substantia nigra begin to degenerate where they decrease the amount of dopamine transmitted to the corpus striatum.  This decrease in dopamine production and release in the striatum leads to an overall net inhibition of the thalamus and communication to the cerebral cortex for proper modulation of motor movements.  When approximately 80% of these dopaminergic neurons within the substantia nigra are depleted, symptoms of Parkinson's disease will begin to manifest.²