Entacapone is a drug that functions as a catechol-O-methyl transferase (COMT) inhibitor. It is used in the treatment of Parkinson's disease. When administered in conjunction with dopaminergic agents such as L-DOPA, entacapone prevents COMT from metabolizing L-DOPA into 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the periphery, which does not easily cross the blood brain barrier (BBB). Pharmacologically, entacapone is somewhat similar to carbidopa or benserazide, in that it is an inhibitor of an enzyme that converts L-DOPA into a compound that cannot cross the blood brain barrier. Carbidopa and benserazide inhibit aromatic L-amino acid decarboxylase, which converts L-DOPA into dopamine, which cannot cross the blood brain barrier. The most frequent undesirable effects caused by entacapone relate to the increased effects of L-DOPA, such as involuntary movements (dyskinesias).
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