Pharmacodynamics
Tolcapone binds to the catalytic center of COMT in both peripheral and central nervous systems with greater affinity than any of the three catecholamine, including levodopa.[7] It thereby prevents the 3-0-methylation of L-DOPA (3-hydroxy-L-tyrosine) by COMT which produces 3-O-methyldopa, a major metabolite that competes with levodopa to cross the blood-brain barrier. Thus, tolcapone improves the bioavailability and reduces the clearance of levodopa and subsequently dopamine from the central nervous system (CNS)