Azathioprine hypersensitivity: report of two cases and review of the literature.

Azathioprine (AZA) is a widely-used drug in the treatment of different diseases such as vasculitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel diseases and in renal transplantation. Side effects of AZA can be classified as toxic, mainly dose related (myelosuppression and hepatotoxicity) and idiosyncratic, mainly dose independent. While the toxic effects are common and well documented, the hypersensitivity reactions are rare and it is not often easy to distinguish them from systemic sepsis or disease recurrence. We report two cases of AZA hypersensitivity occurring in patients with anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis each mimicking a vasculitis relapse or a septic complication of immunosuppression, as well as a review of the literature.