Which chemotherapy drug is known to cause cystitis?

• A. Doxorubicin
• B. Methotrexate
• C. Cyclophosphamide
• D. Vincristine

Answer: (C)

Cyclophosphamide can cause hemorrhagic cystitis because it is metabolized to acrolein, a highly irritating compound that is excreted in the urine and damages the bladder lining. This injury leads to inflammation and bleeding from the bladder mucosa. The risk increases with higher doses and inadequate hydration. Prevention includes good hydration, frequent urination, and the use of mesna, which binds acrolein and neutralizes its irritative effect. Other drugs listed have different toxicity profiles—doxorubicin can cause tissue injury if extravasated but isn’t known for cystitis, methotrexate can cause nephrotoxicity and mucositis, and vincristine is mainly associated with neurotoxicity.