NBME 22 Dextromethorphan (NBME Answers)

NBME 22 Answers ↦

nbme22/Block 2/Question#45 (48.2 difficulty score)
An 86-year-old man who lives in a skilled ...
Dextromethorphan🔍
tags:

+10
submitted by rockediny(10),

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eoDtrx is the ccrotre aenrws ehe.r Frmo het eishocc en,vig teodrx si het lseta kellyi ot ecasu ostipninatoc incse ist nmia shneiamcm fo icntao is ANMD ginamnstoa /wsemo piooid ytiacitv -- it acn uaecs naioptsnocti tub the rteoh siecohc aer MCUH ROEM ikelyl to. sA for mahypierdihnnde = ti is ont ppoaiaterpr rfo llyrede eptaints and ti sint’ an inatsuetv.is

forerofore diphenhydramine and other Gen 1 antihistamines are good choices for chronic cough in allergy and patients with posterior draining and post viral chronic cough (careful with the elderly). That being said, apparently it also causes constipation, so dextro is still the correct answer. +2

passplease Could it also be that you would not prescribe diphenyhyrdramine because they are part of the beers criteria and should be avoided in the elderly? +3

+4
submitted by joanmadd(6),

in NBME 20 there is a question where a pt starts taking an antitussive and has constipation. The offending drug was dextro.... confusing, man...

+3
submitted by noselex(5),

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oretDx vs iedCeno: Btho rae tsae,stniivsu btu xeodrt si more fo NDAM tiogsan hatt saol sah poidoi iogtasn cttyvi.ai eDtrxo is tfeno ebsdua ot egt a airlmis tuo fo bdoy efnelig ude to sit NADM ogastin tef.fce enoiCed on eth torhe horet is a ulfoln- doipio itagn.so s’tI slao ueds as haraenr-li,tdai os nsnioipottca is rvye cmomon rdeseav .fetfce

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pparalpha According to Sketchy and Amboss: dextromethorphan is a weak opioid receptor AGONIST and NMDA receptor ANTAGONIST (it's not an agonist). +5

+0
submitted by calcium196(11),

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oHw si a tshyecnit pdoiio rpherott)nd(ohxeam atth oyu can fdni hwit a 2 scneod ggoole aershc as cnsguia sacptonionti hte rcrceto as?wren Is it sujt eausbce piotrutoim tulwo’nd tater eht gcoh?u

moneysacs Tiotropium would cause constipation bc it’s an anticholinergic. Don’t have any insight into why dextromethorphan is the right answer though, other than process of elimination and diphenhydramine wouldn’t treat his symptoms. +1

upstairs_bumblebee I thought it was dextromethorphan because it would bind NMDA receptors and have weaker opioid effect = less constipation? Idk though :/ +1

dr_salface I agree. I mainly went by way of elimination but even DXM made me think of opiod-induced constipation. Though, all the other answer choices had obvious anticholinergic effects. At least, that was my reasoning for picking dxm. +

+0
submitted by surely_not_a_robot_(0),

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rPe sifrt id.a pDxhtnretohmaroe = tsseiinvuA“t ezainntsg(oa DNMA tgaatuelm rsper).ceot tehcyStin dneeico .gaolna Has dlim oidopi cefeft whne udes ni xecs”se.

I sugse teh key si htat eht oopdii ecfetf si idlm. Smees ielk r’ehtye agnksi chhiw ouldw taetr teh posstmmy dan rcedeu hte dsei ,fctsefe ont sereicnlsya gte dir fo eth desi cestfef epmc.letoly eerAg htat ti is a llnecgihnag eno rfo Setp 1.

-1
submitted by calcium196(11),

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MBNE 20 hsa a stoeiuqn hwti a gyu antkgi reov eht uoecntr cgouh ieodanitcm nda nwo eh ahs noiaptino.sct Wnat to ssueg teh rse?anw tI swa drtoex! ;t&g- 0//ewo8s/a5.msn2tsnmmecneh/rxtaebb:m4/p

oS Im’ ptreyt eusr eth NEBM 22 tesuoniq is just ghrtiats up n.gwor

rockediny No, not so. Dextro *is* the correct answer here. From the choices given, dextro is the least likely to cause constipation since its main mechanism of action is NMDA antagonism w/ *some* opioid activity -- it can cause constipation but the other choices are MUCH MORE likely to. As for diphenhydramine = it is not appropriate for elderly patients and it isn’t an antitussive. +

surely_not_a_robot_ Agreed with @rockediny. Dextro would be the best to prescribe because it has the least amount of constipation out of the drugs that you could prescribe + Anti-cholinergics in the elderly have much more morbidity and risk of mortality. +

keycompany The only way to wrap your head around this is to conclude that Dextro is the "least wrong". I thought a lot about this, and I can't think of any drugs that can suppress cough without also causing constipation, so it makes sense that Dextro is the answer because it is the "least likely" to cause significant constipation. This is probably just a clinical correlate that will be learned during rotations/years in practice. +