Fig. 1.

Combined pharmacokinetic-pharmacodynamic network of thiopurines (thioguanine, mercaptopurine, azathioprine) displayed in the PharmGKB (https://www.pharmgkb.org/pathway/PA2040). Marked with red arrows are two key genes labeled as “very important pharmacogene” are TPMT (thiopurine methyl transferase), inactivating thiopurines, and NUDT15 (nucleoside diphosphate linked moiety X-type motif 15), mediating dephosphorylation of thioguanine phosphates. When deficient, both genes can cause severe toxicity. Clinical biomarker testing is recommended but not yet broadly implemented. PharmGKB grants use of its data and contents under the Creative Commons Attribution-ShareAlike 4.0 International License. PharmGKB, Pharmacogenomics Knowledge Base.