Carbidopa

Carbidopa is an aromatic L-amino acid decarboxylase inhibitor and is usually used together with levodopa. Its main function is to prevent the premature metabolism of levodopa in peripheral tissues, thereby increasing the amount of levodopa that enters the central nervous system. Levodopa is a precursor of dopamine. If it is converted into dopamine by AADC in peripheral tissues, it cannot cross the blood-brain barrier and enter the brain, and it may also cause peripheral side effects such as nausea, vomiting, arrhythmia, and hypotension. Carbidopa, which cannot cross the blood-brain barrier, inhibits AADC activity in peripheral tissues so that levodopa can enter the central nervous system and then be converted into dopamine.