Review Question - QID 212310

A 72-year-old man presents to his physician with complaints of fatigue, night sweats, and an unintentional weight loss of 20 pounds in the past few months. He had previously missed several routine primary care appointments due to feeling generally well until the onset of his current symptoms. Blood tests reveal a leukocyte count of 45,000/mm^3 and a peripheral blood smear demonstrates abnormal findings as shown in Figure A. 4 months after initiating a chemotherapy regimen, the patient develops shortness of breath with exertion. His temperature is 98.7°F (37°C), blood pressure is 128/81 mmHg, pulse is 91/min, respirations are 28/min, and oxygen saturation is 98% on room air. What medication is most likely the cause of the patient’s current symptoms?