Table 3.

TPMT/NUDT Phenotype and Dose of Thiopurines in Inflammatory Bowel Disease

TPMT/NUDT15 phenotype	Starting doses of AZA/6-MP/6-TG
TPMT/NUDT15 wild type	Start with normal dose
TPMT/NUDT15 heterozygote	Start with reduced dose (30%–80%). Dose adjustments to be made every 2–4 weeks
	Close follow up for development of adverse effects (myelosuppression). If myelosuppression occurs, further reduce the dose
TPMT/NUDT15 homozygote	Thiopurines are contraindicated; significant risk of myelosuppression

AZA, 6-MP, and 6-TG are used in doses of 1.5–2.5 mg/kg, 1.0–1.5 mg/kg, and 0.2–0.3 mg/kg respectively.

AZA, azathioprine; 6-MP, 6-mercaptopurine; 6-TG, 6-thioguanine; TPMT, thiopurine-S-methyltransferase; NUDT15, nucleoside diphosphate-linked moiety X-type motif 15.