RESUMO
Metformin is a first-line medication used in the treatment of type 2 diabetes mellitus along with other conditions such as insulin resistance and polycystic ovarian syndrome. Overall, metformin appears to be well tolerated with a low incidence of side effects; however, in certain high-risk populations, it can trigger a hemolytic crisis. This case report describes a middle-aged man who was initiated on metformin for new-onset diabetes, following which he had an acute hemoglobin drop and was diagnosed to be having a hemolytic crisis requiring hospitalization. He was diagnosed with a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) on admission. Extensive workup was done to rule out other causes of hemolysis, all of which came back to be negative. The offending agent was stopped and the patient received supportive care after which he improved. This case highlights a rare, yet important, side effect of metformin that needs to be observed in certain individuals, especially patients with G6PD deficiency. Routine testing of high-risk populations known to be G6PD deficient should be considered before initiating metformin.