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
enzymearomatic 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.[2]
Examples of extracerebral decarboxylase inhibitors include
carbidopa and
benserazide.
Indications
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.[3] 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.[4][5]