Mechanism of Action
Carbidopa
When levodopa is administered orally, it is rapidly decarboxylated to dopamine in extracerebral
tissues so that only a small portion of a given dose is transported unchanged to the central
nervous system. Carbidopa inhibits the decarboxylation of peripheral levodopa, making more
levodopa available for delivery to the brain.
Levodopa
Levodopa is the metabolic precursor of dopamine, does cross the blood-brain barrier, and
presumably is converted to dopamine in the brain. This is thought to be the mechanism whereby
levodopa treats the symptoms of Parkinson's disease.