WBR0755

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A 45 year old man presents to the physician's office complaining of excruciating left great toe pain. The patient explains that he has been having recurrent episodes of the same pain, each lasting for a few days. Physical examination is remarkable for erythema and tenderness of the first metatarsophalangeal joint. Work-up shows elevated levels of uric acid and elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). The physician prescribes a medication that directly inhibits the conversion of hypoxanthine to xanthine and lacks a purine ring. What is the most likely prescribed medication to treat this patient's condition?]]
Answer A	AnswerA::Allopurinol
Answer A Explanation	AnswerAExp::Allopurinol is a xanthine oxidase inhibitor that contains a purine ring.
Answer B	AnswerB::Febuxostat
Answer B Explanation	AnswerBExp::Febuxostat is a xanthine oxidase inhibitor that lacks a purine ring.
Answer C	AnswerC::Probenicid
Answer C Explanation	AnswerCExp::Probenicid is a uricosuric that inhibits the reabsorption of uric acid in the proximal convoluted tubule.
Answer D	AnswerD::Colchicine
Answer D Explanation	AnswerDExp::Colchicine binds and stabilizes tubulin and inhibits polymerization. It impairs chemotaxis and degranulation of leukocytes.
Answer E	AnswerE::Pegloticase
Answer E Explanation	AnswerEExp::Pegloticase is a pegylated recombinant mammalian uricase that converts urate to allantoin, a more soluble and easily excreted compound.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient is presenting with symptoms consistent with gout. The most likely prescribed medication is febuxostat. Febuxostat is a new non-purine xanthine oxidase inhibitor that is considered more potent than allopurinol, which is also a xanthine oxidase inhibitor that contains a purine ring. Xanthine oxidase is an enzyme required for 2 consecutive steps in the pathway of uric acid degradation. Xanthine oxidase inhibition leads to decreased conversion of hypoxanthine to xanthine and similarly, conversion of xanthine to plasma uric acid. Educational Objective: Febuxostat is a xanthine oxidase inhibitor that lacks a purine ring, as compared to allopurinol, which also inhibits xanthine oxidase but contains a purine ring. Reference: Edwards L. Febuxostat: a new treatment for hyperuricaemia in gout. Rheumatology. 2009; 48(2):ii15-ii19. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::allopurinol, WBRKeyword::febuxostat, WBRKeyword::pegloticase, WBRKeyword::colchicine, WBRKeyword::probenicid, WBRKeyword::xanthine, WBRKeyword::oxidase, WBRKeyword::inhibitor, WBRKeyword::inhibitors, WBRKeyword::inhibition, WBRKeyword::gout, WBRKeyword::hyperuricemia, WBRKeyword::podagra, WBRKeyword::acute, WBRKeyword::attack, WBRKeyword::great, WBRKeyword::toe
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