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 are topically used sulfonamides EXCEPT : 
Select and explain. 
A. Sulfacetamide, B. Sulfasalazine, C. Silver sulfadiazine, D. Mafenide
B: Sulfasalazine
Answer: B: Sulfasalazine 
Explanation: None