Objective:To describe the first case of amoxicillin-induced nonimmune hemolytic anemia in a child with glucose-6-phosphate isomerase (GPI) deficiency.Case Summary:A 3-year-old boy with GPI deficiency was admitted for upper respiratory tract infection and fever. The patient was treated with a standard dose of amoxicillin (50 mg/kg/day). On hospital admission, the child had a chronic moderately low hemoglobin level (8.6 g/dL), but within 24 hours of the first amoxicillin dose, the hemoglobin level markedly decreased (5.8 g/dL), the reticulocyte level increased (58%), and the urine darkened. Results of the direct and indirect Coomb's tests were negative and the acute hemolytic phase ended spontaneously 8 days after amoxicillin withdrawal (hemoglobin 9.5 g/dL, reticulocytes 22%).Discussion:All previous cases of amoxicillin-induced hemolytic anemia have been attributed to an immune mechanism. Given the absence of anti-reticulocyte antibodies (Coomb's test), we suggest that the amoxicillin-induced hemolytic anemia in our patient occurred via a nonimmune mechanism favored by the child's GPI deficiency. Based on a MEDLINE search, we believe this to be the first report of amoxicillin-induced nonimmune hemolytic anemia in a child with GPI deficiency. GPI deficiency has been associated with well-compensated chronic hemolytic anemia that can become clinically relevant consequent to the administration of drugs. GPI deficiency can lead to impairment of the system that removes free radicals generated by amoxicillin, thereby resulting in oxidation of hemoglobin and destabilization of red cell membranes, with acute hemolysis and severe hemoglobinuria. The Naranjo probability score was consistent with a probable relationship between the hemolytic anemia and amoxicillin therapy.Conclusions:This report reinforces the hypothesis that a drug-sensitivity reaction is closely related to a genetically transmitted enzyme deficiency.