Question

which statement explains the action of carbidopa-levodopa? carbidopa decreases symptoms of parkinsonism. carbidopa inhibits the breakdown of dopamine at the synapses in the brain. carbidopa inhibits the catechol-o-methyltransferase (comt) enzyme, increasing the concentration of levodopa. carbidopa prevents levodopa decarboxylation in the periphery, resulting in more levodopa being transported to the brain.

Explanation:

• Analyze each option:
• Option 1: Carbidopa itself does not directly decrease Parkinsonism symptoms; levodopa is the active agent for that, so this is incorrect.
• Option 2: Carbidopa does not inhibit dopamine breakdown at synapses. Drugs like MAO - B inhibitors do that, so this is wrong.
• Option 3: Carbidopa is a decarboxylase inhibitor, not a COMT inhibitor. COMT inhibitors (e.g., entacapone) work on COMT, so this is incorrect.
• Option 4: Carbidopa is a peripheral decarboxylase inhibitor. It stops levodopa from being decarboxylated (converted to dopamine) in the periphery. This means more levodopa can cross the blood - brain barrier and be converted to dopamine in the brain, which is the correct mechanism of carbidopa - levodopa.

Answer:

D. Carbidopa prevents levodopa decarboxylation in the periphery, resulting in more levodopa being transported to the brain.