An aromatic L-amino acid decarboxylase inhibitor (synonyms: DOPA decarboxylase inhibitor, Extracerebral decarboxylase inhibitor, DDCI and AAADI) is a medication of type enzyme inhibitor which inhibits the synthesis of dopamine by the enzyme aromatic L-amino acid decarboxylase (AADC, AAAD, or DOPA decarboxylase). It is used to inhibit the decarboxylation of L-DOPA to dopamine outside the brain, i.e. in the blood. This is primarily co-administered with L-DOPA to combat Parkinson's disease. Administration can prevent common side-effects, such as nausea and vomiting, as a result of interaction with D2 receptors in the vomiting center (or cheomoreceptor trigger zone) located outside the blood–brain barrier.[1]
Examples of extracerebral decarboxylase inhibitors include carbidopa and benserazide.
Peripherally selective DDCIs incapable of crossing the protective blood–brain barrier (BBB) are used in augmentation of L-DOPA (levodopa) in the treatment of Parkinson's disease (PD) to block the conversion of L-DOPA into dopamine outside the brain, for the purpose of reducing adverse side effects.[2] Combined L-DOPA and DDCI therapy does not inherently decrease peripheral cardiovascular side effects of L-DOPA administration; however, combined therapy potentiates the central effects of L-DOPA by decreasing the dose-dependency 4-5 fold, therein allowing for effective Parkinson's disease treatment without cardiovascular risk associated with high peripheral dopamine.[3] [4]