Adjustment of azathioprine dose should be based on a lower 6-TGN target level to avoid leucopenia in NUDT15 intermediate metabolisers.

NUDT15 polymorphisms were associated with time-to-leucopenia during azathioprine treatment in Korean paediatric patients with IBD. In order to reduce the development of thiopurine-induced leucopenia (<15%) in NUDT15 intermediate metabolisers, adjustment of azathioprine doses should be based on a lower 6-TGN target level (<167.1 pmol/8 × 108 RBC).