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NBME 21 Answers

nbme21/Block 4/Question#29 (28.8 difficulty score)
A 22-year-old man comes to the physician ...
Formation of destructive free radicals🔍
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This is a picture of Giardia lamblia… caused by drinking contaminated water with cysts.

Multinucleated trophozoites

Rx -- Metronidazole -- forms toxic free radical metabolites in the bacterial cell that damage DNA = BACTERICIDAL

qball  This is testing our knowledge in a FAIR way. Why cant there be more questions like this instead of them trying to trick us, have poorly worded questions or have us pick the least shitty answer. End of rant. +1  



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nieotailzd erferdrpe ude ot gensli osde

sweetmed  or metronidazole +  
niboonsh  what would his diagnosis be tho? +  
lostweightthxnorovirus  @niboonsh Giardia I believe. the trophozoite is pictured in the problem and has a classic "shield-like" appearance. FA 2019 pg. 155 has more information and the sketchy for it was really good! +1  
nwinkelmann  Per FA, DOC for giardia = metronidazole. MOA of metronidazole = formation of toxic free radical metabolites in the bacterial cell wall that damage DNA making it bactericidal and antiprotozoal. Metro treats = GET GAP = giardia, entamoeba, trichomonas, Gardnerella, anaerobes (below diaphragm), and H. pylori (as an alternative to amoxicillin in PCN allergy). Adverse effects = disulfiram-like reaction, HA, and metallic taste. I didn't know what Tinidazole is, and found out it is of the same drug class as Metronidazole, so makes sense why it would also be used for Giardia. For the purpose of the UMSLE 1, though, I think metronidazole would be DOC (especially because tinidazole isn't in FA). +2  
mannywillsee  This little bug has has a face, and now you can't unsee it either! +  



Is there any drug which would cause enhancement of cell membrane permeability to chloride? It seems like the MOA of ETEC & V. cholerae adenylate cyclase toxins and somewhat that of Ivacaftor used in cystic fibrosis.

kevin  For the purposes of STEP 1 I don't think there is an antibiotic that would do that. If you wanted to really stretch the definition of enhanced cell permeability you could go with a polymixin which is essentially a detergent for bacterial membranes and can be used rarely for pseudomonas and other bacteria +