Review Question - QID 212760

A 26-year-old man presents to the emergency department complaining of vomiting and abdominal pain. He states that the abdominal pain started 2 days ago and is diffuse. The vomiting began around the same time, and is non-bloody and non-bilious. He has not been able to tolerate food or drink all day. He has also noticed darker urine. He endorses that he had an ear infection a week ago and was started on a short-course of an antibiotic. His ear pain has since resolved. The patient’s temperature is 100.4°F (37°C), blood pressure is 109/62 mmHg, pulse is 114/min, and respirations are 26/min. On physical examination, pallor and moderate icterus are noted. Labs are drawn that show a hemoglobin of 9.3 with a reticulocyte count of 5%, a serum total bilirubin of 24.95 mg/dL, and a direct bilirubin of 3.43 mg/dL. A peripheral smear is obtained, as shown in Figure A, with arrows indicating abnormal cells. A Prussian blue stain of the urine is positive. Which of the following is the most likely cause of the patient’s presentation?