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 cause discolouration of urine EXCEPT : 
Select and explain. 
A. Nitrofurantoin, B. Digoxin, C. Azo dyes, D. Rifampicin
B: Digoxin
Answer: B: Digoxin 
Explanation: None