This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Prior to general anesthesia and surgery which oral hypoglycemic drug should be discontinued? 
Select and explain. 
A. Piglitazone, B. Metformin, C. Glybenclamide, D. Glyclazide
B: Metformin
Answer: B: Metformin 
Explanation: None