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
Sterile haemorrhagic cystitis is caused by ? 
Select and explain. 
A. Busulfan, B. Ketoprofen, C. Methicillin, D. Cylclophosphamide
D: Cylclophosphamide
Answer: D: Cylclophosphamide 
Explanation: Ans. is `d' i.e., Cyclophosphamide "Haemorrhagic cystitis can develop in patients receiving cyclophosphamide or ifosfamide." o Hemorrhagic cystitis due to cyclophosphamide is attributed to the presence of its metabolite ACROLEIN in urine. Other drugs causing hemorrhagic cystitis Carmustine o Extended spectrum penicillins o Vincristine Chlorambucil o Nitrogen mustard o Busulfan