This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sedative-Hypnotics and Parkinsonism, Subject name: Pharmacology
DOC for Levodopa induced vomiting is? 
Select and explain. 
A. Metoclopramide, B. Ondansetron, C. Doxylamine, D. Domperidone
D: Domperidone
Answer: D: Domperidone 
Explanation: Domperidone crosses blood brain barrier poorly. The anti-emetic action is exeed mainly through CTZ which is not protected by blood brain barrier. Because of poor entry into CNS, it does not block the therapeutic effect of Levodopa in Parkinsonism, but counteracts its dose limiting emetic action. It is a D2 receptor antagonist, chemically related to haloperidol, but pharmacologically related to Metoclopramide.