This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Adverse Drug Effect, Subject name: Pharmacology
Haemorrhagic cystitis is caused by 
Select and explain. 
A. Cyclophosphamide, B. Busulphan, C. Prednisolone, D. Melphalan
A: Cyclophosphamide
Answer: A: Cyclophosphamide 
Explanation: Ans. is 'a' i.e., Cyclophosphamide Hemorrhagic cystic is most commonly associated with cyclophosphamide (seen in 5-10 % of patients).In Harrison drugs causing hemorrhagic cystitis have been listed and this also includes Busulphan.Still, I prefer cyclophosphamide as the answer because none of the pharmacology books (This even includes Goodman & Gilman) mention hemorrhagic cystitis as an adverse effect of Busulfan.More question on this topic: -Hemorrhagic cystitis has been attributed to cyclophosphamide because of the presence of acrolein.Adequate hydration and intravenous injection of MESNA (Sodium 2-mercaptoethane sulfonate) minimize this problem.