**Question:** In treatment of Parkinsonism, L–Dopa is combined with carbidopa mainly:

A. To reduce the peripheral side effects of L-Dopa
B. To increase the bioavailability of L-Dopa
C. To enhance the anti-Parkinsonian effects of L-Dopa
D. To reduce the frequency of L-Dopa administration

**Correct Answer:** A. To reduce the peripheral side effects of L-Dopa

**Core Concept:** Parkinsonism is a neurological disorder characterized by motor symptoms such as tremors, rigidity, bradykinesia, and postural instability. L-Dopa, a precursor to dopamine, is a commonly used medication to treat Parkinsonism because of its ability to cross the blood-brain barrier and increase dopamine levels in the central nervous system (CNS).

**Why the Correct Answer is Right:** Carbidopa is an enzyme inhibitor that specifically blocks the peripheral decarboxylase enzyme, which is responsible for converting L-Dopa into dopamine in the gastrointestinal tract. By inhibiting this enzyme, carbidopa prevents L-Dopa from being broken down in the gut, allowing a higher proportion of L-Dopa to reach the CNS where it is effective in treating Parkinsonism.

**Why Each Wrong Option is Incorrect:**

A. B. C. D.

**Option A:** Reducing the peripheral side effects of L-Dopa is correct because carbidopa helps prevent L-Dopa from being converted into dopamine in the periphery, reducing the risk of side effects such as nausea, flushing, and dizziness associated with L-Dopa administration.

**Option B:** Increasing the bioavailability of L-Dopa is incorrect because the purpose of combining L-Dopa with carbidopa is to prevent peripheral conversion, not to increase its bioavailability.

**Option C:** Enhancing the anti-Parkinsonian effects of L-Dopa is incorrect because the primary purpose of combining L-Dopa with carbidopa is to reduce peripheral side effects, not to increase the drug's therapeutic efficacy in the CNS.

**Option D:** Reducing the frequency of L-Dopa administration is incorrect as the primary reason for combining L-Dopa with carbidopa is to prevent peripheral conversion, not to reduce the administration frequency.

**Clinical Pearl:** In summary, the correct combination of L-Dopa with carbidopa helps in the treatment of Parkinsonism by preventing L-Dopa from being converted into dopamine in the periphery, thereby reducing the risk of peripheral side effects and allowing higher concentrations of L-Dopa to reach the CNS, where it can alleviate motor symptoms in patients with Parkinson's disease.