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NBME 22 Answers

nbme22/Block 3/Question#18 (35.5 difficulty score)
An 85-year-old woman is diagnosed with a ...
Morphine is metabolized to active metabolites that accumulate🔍
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 +11  upvote downvote
submitted by moloko270(60),
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staygoodpupper  Morphine mostly undergoes phase II metabolism and is then excreted renally. Some of the metabolites are metabolically active, and her creatinine was a little elevated, so renal clearance could have been impaired. +9  
celedkin  http://www.labpedia.net/test/177 the diagram in this article is useful to follow the metabolism of morphine +1  



 +0  upvote downvote
submitted by drzed(177),

Unfortunately, I chose (C) thinking that the down-regulation of receptors would lead to needing higher doses for efficacy (patient is using a patient controlled pump), however tolerance to miosis does not develop, and thus eventually this side effect would occur.

Could anyone point out where my train of thought is incorrect? I suspect that my assumption of the patient increasing their dose is not warranted?

aag  I also chose this, @drzed but looking back, if there was down-regulation of the receptors then she wouldnt have enough receptors to cause altered mental status and respiratory depression, side effects that you do develop tolerance to. How I would have remembered that morphine is metabolized to other active metabolites is beyond me. Happy studying hope this helps. +1  
waterloo  He's also on a controlled analgesic pump. I've been on one before, and basically you can't keep pumping yourself constantly with it. You can hit the button, get a small dose, and then have to wait a bit of time to hit it again. The next time you hit the effect (at least for me) was always the same meaning I wasn't becoming tolerant to it (I was on one for a week). This controlled pump phrase has come up in another exam, which makes me think when they say that they want you to think this isn't someone who's taking alot of meds all the time. I also like aag thought process. +