WBR0507

Author	[[PageAuthor::Gonzalo A. Romero, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology, MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 2-year-old girl is brought to the pediatrician because her mother is concerned about her teeth being darker than usual, even though she has been brushing her daughter’s kid consistently. She states that at week 8 of pregnancy, she developed a ring-like rash in the leg after a camping trip, for which she took leftover antibiotic from her brother when he developed a similar rash after a boy-scout excursion into rural Connecticut. Which of the following mechanisms of action corresponds to the most likely drug used?]]
Answer A	AnswerA::Prevents attachment of aminoacyl-tRNA
Answer A Explanation	[[AnswerAExp::Correct. See overall explanation]]
Answer B	AnswerB::Inhibits the formation of initiation complex
Answer B Explanation	[[AnswerBExp::Incorrect. This is the mechanism of action of aminoglycosides used for gram negative rod infections]]
Answer C	AnswerC::Blocks translocation
Answer C Explanation	[[AnswerCExp::Incorrect. This is the mechanism of action of macrolides, used to treat atypical pneumonias (Mycoplasma, Chlamydia, Legionella), URiI, STDs, gram-positive cocci (streptococcal infections in patients allergic to penicillin), and Neisseria]]
Answer D	AnswerD::Require 02 for uptake;
Answer D Explanation	[[AnswerDExp::Incorrect. This refers to aminoglycosides]]
Answer E	AnswerE::Inhibit peptidyl-transferase action
Answer E Explanation	[[AnswerEExp::Incorrect. This is the mechanism of action of chloramphenicol]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The clinical vignette describes a patient who delivered a child who currently has discolored teeth. She took an antibiotic during pregnancy to treat Lyme’s disease. The treatment of choice of Lyme disease is tetracycline, which is contraindicated in pregnancy due to bone and teeth malformation. Tetracycline, specifically doxycycline inhibits the protein synthesis by binding to the 30s ribosomal subunit and preventing the aminoacyl-tRNA attachment. Educational objective: tetracycline use during pregnancy is associated with teeth discoloration (teratogenic) Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Teratogen
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::