<unk>  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.<unk>  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 availability 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. The use of<unk>  seems counter-intuitive in Parkinson's disease (PD) in that it prevents DDC conversion of levodopa/L-DOPA to dopamine. However, exogenously provided, levadopa/L-DOPA gets metabolized peripherally to its active metabolite dopamine before reaching the blood–brain barrier. Therefore, the PD brain, which is deficient in dopamine, will not receive as much of its prodrug precursor levodopa/L-DOPA due to peripheral DDC breakdown. However,<unk>  can decrease peripheral DDC conversion of levodopa/L-DOPA before it crosses the blood–brain barrier.<unk>  acts as a peripheral DDC inhibitor, as<unk> , itself, cannot cross the blood–brain barrier. In other words,<unk>  has no effect on brain DDC conversion of levodopa/L-DOPA to dopamine. Ultimately, a greater proportion of the exogenously provided levodopa/L-DOPA reaches the brain. Commercially,<unk> /levodopa combinations are available in the treatment of central dopamine deficiencies. Along with<unk> , other DDC inhibitors are benserazide (Ro-4-4602), difluromethyldopa, and α-methyldopa.
Carbidopa
Ciladopa
Droxidopa
Glybuzole
Glysobuzole
Fluorodopa
Droperidol
Memantine