A patient with acute myeloid leukemia receives high-dose cyclophosphamide before hematopoietic stem cell transplantation. Which agent is most likely to decrease the toxicity of this regimen?

• A. Amifostine
• B. Leucovorin
• C. Filgrastim
• D. MESNA

Answer: (D)

High-dose cyclophosphamide can produce a urotoxic metabolite called acrolein, which damages the bladder lining and can cause hemorrhagic cystitis. MESNA (sodium 2-mercaptethanesulfonate) provides sulfhydryl groups that bind acrolein in the urine, forming non-toxic conjugates and preventing bladder injury. This makes MESNA the best choice to decrease the regimen’s toxicity in the HSCT setting.

Other agents don’t target this specific toxicity. Amifostine is used to reduce platinum- and radiation-related toxicities, mainly kidney protection with cisplatin, not acrolein-related bladder damage. Leucovorin rescues normal cells from methotrexate toxicity, not cyclophosphamide. Filgrastim (G-CSF) boosts neutrophil recovery but doesn’t prevent acrolein-induced bladder injury.