Certified Neuroscience Registered Nurse (CNRN) Practice Exam

What is the primary mechanism of action for Carbidopa in the treatment of Parkinson's disease?

1. Inhibits the enzyme dopa decarboxylase

2. Stimulates dopamine receptors

3. Increases acetylcholine release

4. Blocks serotonin receptors

The correct answer is: Inhibits the enzyme dopa decarboxylase

Carbidopa's primary mechanism of action in the treatment of Parkinson's disease is the inhibition of the enzyme dopa decarboxylase. This enzyme is responsible for the conversion of levodopa to dopamine in the peripheral tissues. By inhibiting this enzyme, carbidopa ensures that more levodopa remains available to cross the blood-brain barrier where it can then be converted to dopamine within the central nervous system. This effective increase in central dopamine levels alleviates the motor symptoms associated with Parkinson's disease. This action is crucial because if levodopa was converted to dopamine in the periphery, it could lead to increased side effects without carrying the therapeutic benefit to the brain. Therefore, by inhibiting dopa decarboxylase, carbidopa enhances the efficacy of levodopa, allowing for lower doses and minimizing peripheral side effects. The other options do not accurately describe the role of carbidopa. For instance, carbidopa does not stimulate dopamine receptors or increase acetylcholine release, nor does it block serotonin receptors. Its specific action on dopa decarboxylase is what differentiates its role in therapy and highlights its importance in optimizing the treatment of Parkinson's disease.