Catechol-O-methyltransferase (COMT) Inhibitors Mechanism of action—

Entacapone and tolcapone are inhibitors of COMT, the enzyme in both the CNS and peripheral tissues that converts levodopa to 3-O-methyldopa(3OMD). Increased plasma levels of 3OMD are associated with poor response to levodopa partly because the compound competes with levodopa for active transport into the CNS. Entacapone acts only in the periphery.