Nonimmediate allergic reactions induced by Mesna

Mesna (2‐mercaptoethane sulfonate Na), a drug that alleviates cyclophosphamide (CYC)‐induced hemorrhagic cystitis, is frequently used to treat cancer and collagen diseases. A 33‐year‐old woman presented with high fever during CYC‐based induction therapy for systemic lupus erythematosus. Her final diagnosis was mesna‐induced drug hypersensitivity. Although mesna is widely used, allergic reactions are rare. This may be because of misdiagnosis as a primary disease flare‐up, infection, or CYC‐induced hypersensitivity reaction, which are commonly reported. Thus, accurate diagnosis is important for completion of the CYC‐based regimen.