WBR0327

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Hematology
Prompt	[[Prompt::A 3 year old African American boy is brought by his parents to the emergency department for irritability and swelling in the hands and feet. Peripheral smear (shown below) demonstrates findings consistent with the patient's condition. The patient is started on a chemotherapeutic agent to relieve his symptoms. By what mechanism does the prescribed medication help relieve the patient's symptoms? ]]
Answer A	AnswerA::Increase in HbF levels
Answer A Explanation	AnswerAExp::Hydroxyurea is especially beneficial in patients with sickle cell disease (SCD) because it increases HbF levels.
Answer B	AnswerB::Decrease in thymidylate synthase activity
Answer B Explanation	AnswerBExp::5-Fluorouracil is known to inhibit thymidylate synthase.
Answer C	AnswerC::Increase in ribonucleotide reductase activity
Answer C Explanation	AnswerCExp::Hydroxyurea inhibits ribonucleotide reductase.
Answer D	AnswerD::Increase in HbA levels
Answer D Explanation	AnswerDExp::Patients with SCD have low HbA levels.
Answer E	AnswerE::Systemic vasodilatory effect
Answer E Explanation	AnswerEExp::Vasodilation is helpful for patients with SCD, but this is not the mechanism by which hydroxyurea is beneficial for these patients.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient is most likely diagnosed with sickle cell disease. Peripheral smear shows sickle-looking red blood cells that are consistent with the diagnosis. Patients with sickle cell disease require hydroxyurea, which provides symptomatic relief by increasing HbF levels. HbF has high affinity for oxygen and may thus delivery of oxygen to peripheral tissues in patients with SCD will be facilitated with hydroxyurea. Hydroxyurea is originally a chemotherapeutic agent that inhibits ribonucleotide reductase to decrease DNA synthesis at the S-phase. It is usually used for cancers such as melanoma and CML. Common side effects of hydroxyurea include Gi symptoms, bone marrow suppression, and increased risk of developing leukemias. Educational Objective: Hydroxyurea is used in patients with sickle cell disease to increase HbF levels. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::HbF, WBRKeyword::hemoglobin, WBRKeyword::hemoglobinopathy, WBRKeyword::hemoglinopathies, WBRKeyword::sickle, WBRKeyword::cell, WBRKeyword::disease, WBRKeyword::peripheral, WBRKeyword::smear, WBRKeyword::HbC, WBRKeyword::HbS, WBRKeyword::hydroxyurea, WBRKeyword::therapeutic, WBRKeyword::effect
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