This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Entacapone may be useful in patients being treated with levodopa-carbidopa combination because it : \nSelect and explain. \nA. Activates COMT, B. Decreases formation of 3–OMD, C. Inhibits monoamine oxidase type B, D. Inhibits dopamine uptake', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Levodopa is converted to dopamine by dopa decarboxylase (that cannot cross the blood-brain barrier).\nCarbidopa is an inhibitor of dopa decarboxylase in the periphery. It therefore increases the amount of l-dopa that reaches the brain (due to inhibition of peripheral metabolism to dopamine).\nDue to inhibition of l-dopa metabolism (by dopa decarboxylase), an alternative pathway of metabolism by catechol-O-methyl transferase (COMT) is activated.\nCOMT metabolizes l-dopa to 3-O-methyldopa (3-OMD) that can complete with l-dopa for entry in the brain.\nEntacapone and tolcapone is useful in Parkinsonism by inhibiting COMT.', 'role': 'assistant'}]