Azathioprine Therapy in a Pediatric TPMT-Deficient Patient—Still an Option

: We describe the case of a pediatric patient on azathioprine therapy with previously undiagnosed homozygote thiopurine S-methyltransferase (TPMT) deficiency, resulting in myelotoxic thiopurine metabolite levels. The patient was successfully treated with a very low azathioprine dose of 50 mg once a week (4% of standard dose), guided by frequent thiopurine metabolite measurement and a close clinical surveillance. We demonstrate that azathioprine therapy still might be an effective and safe therapeutic option in pediatric thiopurine S-methyltransferase-deficient IBD patients.