Entacapone is an anti–Parkinsonism drug. It acts by :
**Core Concept**
Entacapone is a catechol-O-methyltransferase (COMT) inhibitor, which plays a crucial role in the metabolism of dopamine in the brain. By inhibiting this enzyme, entacapone increases the availability of dopamine in the synaptic cleft, thereby alleviating symptoms of Parkinson's disease.
**Why the Correct Answer is Right**
Entacapone works by competitively inhibiting the activity of COMT, an enzyme responsible for the degradation of catecholamines, including dopamine. This inhibition leads to an accumulation of dopamine in the synaptic cleft, which in turn enhances dopaminergic transmission and improves motor function in patients with Parkinson's disease. The primary site of action of entacapone is in the peripheral circulation, where it prevents the breakdown of levodopa and dopamine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because entacapone is not a monoamine oxidase B (MAO-B) inhibitor, which is a different class of drugs used in the treatment of Parkinson's disease.
**Option B:** This option is incorrect because entacapone does not act by inhibiting the reuptake of dopamine, which is a mechanism of action of certain other drugs used in the treatment of Parkinson's disease.
**Option C:** This option is incorrect because entacapone does not act by blocking dopamine receptors, which is a mechanism of action of certain other drugs used in the treatment of Parkinson's disease.
**Clinical Pearl / High-Yield Fact**
It is essential to note that entacapone is often used in combination with levodopa and carbidopa to enhance the efficacy of levodopa therapy and reduce the risk of levodopa-induced fluctuations.
**Correct Answer: C. Inhibiting catechol-O-methyltransferase (COMT) enzyme**