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
All of the following drugs undergo hepatic metabolism before excretion EXCEPT: 
Select and explain. 
A. Phenytoin, B. Diazepam, C. Penicillin G, D. Cimetidine
C: Penicillin G
Answer: C: Penicillin G 
Explanation: None