Prevention of mercaptopurine‐induced hypoglycemia using allopurinol to reduce methylated thiopurine metabolites

Skewing of mercaptopurine (6‐MP) metabolism preferentially toward the 6‐methylmercaptopurine (6‐MMP) metabolite over the antileukemic metabolite 6‐thioguanine (6‐TGN) is associated with 6‐MP‐related hepatotoxocity. Allopurinol when coadministered with 6‐MP can reduce this skewing and ameliorate the associated adverse effects. The cases we report here demonstrate that aberrant overproduction of 6‐MMP is also associated with profound 6‐MP‐associated hypoglycemia, which can be reversed by administration of allopurinol. This case series contributes to the scant literature on 6‐MP‐induced hypoglycemia and provides evidence that addition of allopurinol to reduced dose 6‐MP can successfully manage this severe toxicity.