Fasting hypoglycemia is common during maintenance therapy for childhood acute lymphoblastic leukemia.

Nineteen of 35 children (54%) with acute lymphoblastic leukemia receiving maintenance therapy consisting of daily oral 6-mercaptopurine and weekly oral methotrexate developed hypoglycemia (blood glucose level <2.7 mmol/L [50 mg/dL] or <2.9 mmol/L [54 mg/dL] with symptoms) during 16 hours of overnight fasting. In 15 of 15 re-studied children, fasting tolerance had improved, and in 67% (10/15), it had become normal a few months after cessation of therapy.