An 8-year-old boy is brought to the physician because of a 1-day history of severe left hand pain. He has had similar painful episodes in the past that required hospitalization. Physical examination shows pale conjunctivae. There is tenderness on palpation of the wrist and the small joints of the left hand. Peripheral blood smear shows crescent-shaped erythrocytes. He is started on a pharmacologic agent that is known to cause macrocytosis. This drug causes an arrest in which of the following cell cycle phases?

Question

Quizplus · Accepted Answer

Eductional Objective: The S phase of the cell cycle will be arrested in a patient taking hydroxyurea. Hydroxyurea has toxic effects on the bone marrow and it has been shown to induce an atypical form of macrocytosis (nonmegaloblastic anemia) characterized by the presence of volumetric macrocytes. It is important to note that these macrocytes are different from the megaloblasts seen in megaloblastic anemia. S phase inhibition and macrocytosis are observed in a wide range of drugs with toxic effects on the bone marrow (e.g., methotrexate, adriamycin, purine antagonists, pyrimidine antagonists, and alkylating agents).

An 8-Year-Old Boy Is Brought to the Physician Because of a 1-Day