MON-065 Prevention of 6-Mercaptopurine-Induced Hypoglycemia by Levocarnitine Replacement

Background: Symptomatic hypoglycemia has been reported in children less than 6 years of age receiving 6-Mercaptopurine for acute lymphoblastic anemia (ALL); however, the mechanism of 6-Mercaptopurine-induced hypoglycemia has been unclear. Objective: The objective was to investigate the metabolism in a 3-year-old patient with hypoglycemia induced by 6-Mercaptopurine during maintenance therapy for ALL. Methods: We reviewed test results including serum total and free carnitine levels at time of hypoglycemia in a 3-year-old child with ALL who had repeatedly low plasma glucose as a side effect of 6-Mercaptopurine. Hypoglycemia defined as plasma glucose <50 mg/dL was detected using a glucose meter and each time verified in the clinical laboratory. After Levocarnitine was added to 6-Mercaptopurine therapy, the glycemic control was assessed using a glucose meter, the clinical laboratory, and a continuous glucose monitor; serum total and free carnitine levels were repeated when hypoglycemia resolved. Results: Our patient presented with fatigue, tremors and plasma glucose 39 mg/dL to 47 mg/dL, corrected with a sugary beverage. He had plasma ACTH 38 pg/mL, serum cortisol 10 mcg/dL, total carnitine 24 nmol/mL (expected 35 - 84), free carnitine 18 nmol/mL (expected 24 - 63), plasma free fatty acids 1.62 mmol/L (expected >1.5), beta-hydroxybutyrate of 0.2 mmol/L to 0.7 mmol/L (expected >2.0), and urine ketone bodies negative when plasma glucose was between 33 mg/dL and 39 mg/dL. Plasma insulin was undetectable at time of hypoglycemia, and serum glucose increased by less than 30 points in response to Glucagon IV. Serum IGF-1 as measure of growth hormone effect and thyroid function were normal. Hypoglycemia continued to daily recur especially during the night despite bedtime snacks high in complex carbohydrates and was prevented only by Levocarnitine 25 mg/kg/dose every 12 hours PO that raised serum total and free carnitine levels. The patient remained hypoglycemia-free one month after Levocarnitine was added to 6-Mercaptopurine therapy, in particular, he had average glucose 114 mg/dL with standard deviation 30 mg/dL, glucose 70 mg/dL to 140 mg/dL 93% of the time, and glucose <55 mg/dL 0% of the time. Conclusions: Our patient had symptomatic hypoketotic hypoglycemia related to moderately reduced serum total and free carnitine, corrected with Levocarnitine replacement. Increase in plasma free fatty acids without expected increase in plasma and urine ketone bodies may be sign of impaired synthesis of carnitine, which is required for transport of fatty acids into the mitochondria to produce ketone bodies. Measuring serum total and free carnitine in hypoglycemia induced by 6-Mercaptopurine is helpful in identifying children, who may benefit from Levocarnitine replacement.