WBR0529

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::To study the effects of a newly developed drug, a researcher uses polarized microscopy to monitor the changes in living Pectinaria oocytes exposed to intermittent doses of this agent. Although most oocytes are not directly affected, those in active replication seem to arrest at a certain point during mitosis with a significant reduction in the size of meiotic spindles, as measured by loss of birefringence under polarized light. The researcher also notices that shortly after the drug is washed, mitosis would resume and the spindles would regain birefringence. Which of the following drugs most likely has the same mechanism of action?]]
Answer A	AnswerA::Carboplatin
Answer A Explanation	AnswerAExp::Carboplatin is a chemotherapeutic agent that cross-links DNA.
Answer B	AnswerB::Amantadine
Answer B Explanation	AnswerBExp::Amantadine is an antiviral drug that inhibits influenza uncoating by binding to the M2 protein.
Answer C	AnswerC::Griseofulvin
Answer C Explanation	AnswerCExp::Griseofulvin is a fungistatic agent that inhibits microtubule polymerization and inhibits mitosis.
Answer D	AnswerD::Etoposide
Answer D Explanation	AnswerDExp::Etoposide is an antineoplastic agent that acts as a topoisomerase inhibitor.
Answer E	AnswerE::Caspofungin
Answer E Explanation	AnswerEExp::Caspofungin is an antifungal drug that inhibits the enzyme β-glucan synthase and disturbs the integrity of the fungal cell wall.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Griseofulvin is a fungistatic antifungal drug used mostly in the treatment of fungal skin infections. It is deposited in keratin precursor cells and tightly bound to keratin, which explains its efficacy in dermatologic infections. It acts by inhibiting mitosis strongly in fungal cells and weakly in mammalian cells by affecting mitotic spindle microtubule function. It binds to microtubules and inhibits their ability to polymerize leading a decrease in the effective mitotic spindles. It is among the fastest reversible drugs acting on microtubules. Common side effects include urticaria and drug induced rashes. A more severe but rare adverse effect is severe liver toxicity. Treatment is indicated for resistant infections affecting skin, body, hair, or nails, including tinea capitis, tinea corporis, and tinea pedis. Educational Objective: Griseofulvin is a fungistatic agent that inhibits microtubule polymerization halting mitotic divison. References: Odds FC, Brown AJ, Gow NA. Antifungal agents: mechanisms of action. Trends in Microbiology. 2003;11(6):272-279.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Griseofulvin, WBRKeyword::Microtubule, WBRKeyword::Mitosis, WBRKeyword::Antifungal, WBRKeyword::Fungistatic, WBRKeyword::Fungal infection
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