This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Histamine, 5-HT and PGs, Subject name: Pharmacology
Which of the following drug is not used for prophylaxis of migraine? 
Select and explain. 
A. Topiramate, B. Propranolol, C. Flunarizine, D. Ethosuximide
D: Ethosuximide
Answer: D: Ethosuximide 
Explanation: Propranolol is the most commonly used drug for prophylaxis of migraine attacks. Timolol, atenolol, metoprolol and nadolol can also be used but the drugs with ISA (e.g. pindolol) are ineffective. Calcium channel blockers like flunarizine (also blocks Na+ channels) is also effective. Diltiazem, verapamil and nimodipine can also be used. Methysergide, cyproheptadine and TCAs like amitriptyline, imipramine and noriptyline can also be used. Clonidine can be used orally for the prophylaxis of migraine attacks. Topiramate (anticonvulsant drug) has recently been approved for prophylaxis of migraine Valproate and gabapentin also possess some prophylactic activity.