Anagen Effluvium as an Early Sign of Azathioprine Toxicity.

Azathioprine is a purine analog which is Food and Drug Administration (FDA) approved for organ transplant and severe rheumatoid arthritis (RA). Off-label use in dermatological diseases like immunobullous diseases, atopic dermatitis, autoimmune connective tissue disorders like systemic lupus erythematosus (SLE) and dermatomyositis, and other medical conditions like Crohn's disease, Churg-Strauss syndrome, and myasthenia gravis has long been in the picture.^1-3 The active metabolite of this prodrug is 6-thioguanine (6-TG), which gets incorporated into DNA/RNA structure, causing decreased purine metabolism resulting in its immunosuppressive effect. Thiopurine methyltransferase (TPMT) converts 6-mercaptopurine (6-MP) to an inactive metabolite. TPMT deficiency will cause increased conversion of 6-MP to active metabolite 6-TG, which increases the risk of myelosuppression, one of the life-threatening side effects of the drug.^1,2.