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
Hemorrhagic cystitis is caused by : 
Select and explain. 
A. Cyclophosphamide, B. 6 Mercaptopurine, C. 5 Fluorouracil, D. Busulfan
A: Cyclophosphamide
Answer: A: Cyclophosphamide 
Explanation: Cyclophosphamide is a prodrug and is activated by hepatic biotransformation to aldophosphamide. One of its degrada­tion products is acrolein that is responsible for hemorrhagic cystitis (its characteristic adverse effect). This adverse effect can be decreased by vigorous hydration and by the use of mercapto ethane sulfonic acid (mesna).