Carbidopa (CDP)

Carbidopa inhibits aromatic-L-amino-acid decarboxylase (DOPA Decarboxylase or DDC), an enzyme important in the biosynthesis of L-tryptophan to serotonin and in the biosynthesis of L-DOPA to Dopamine (DA). DDC exists both outside of (body periphery) and within the confines of the blood–brain barrier. Carbidopa is used in the treatment of, among other diseases, Parkinson's disease (PD), a condition characterized by death of dopaminergic neurons in the substantia nigra. Increased dopamine available may increase the effectiveness of the remaining neurons and alleviate symptoms for a time. The pharmacologic objective is to get an exogenous dopamine-precursor known as levodopa/L-DOPA into the dopamine-deficient brains of PD patients. Levodopa/L-DOPA can cross the blood brain barrier, but dopamine cannot.