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Retired NBME 23 Answers

nbme23/Block 4/Question#26 (reveal difficulty score)
A 28-year-old man has hypertriglyceridemia ...
Aspirin ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—lfsuarez(160)
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When patients are given Nicotinic acid(Niacin) they are told to expect common side effects to occur such as warmth and redness. One can avoid these side effects by taking aspirin

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mcl  To expand on this, the flushing/warmth/redness is due to release of PGD2 and PGE2 which is why taking an NSAID helps. +20
snripper  Doesn't acetaminophen inhibits COX 1-2, too? Why can't you use that instead of aspirin? Just wondering. +4
raspberryslushy  I had this same question too, and had it narrowed down to those two choices. Ended up going w/aspirin but it was sort of a coin toss. Still not sure why it's not acetaminophen. +
eagleeeee  I think the reason is that acetaminophen is inhibited peripherally and is mainly used to inhibit COX in the CNS +8
whatup  The worst side effect of Niacin is hepatotoxicity. Acetaminophen is famously known for hepatoxicity so aspirin is a better answer +4
doctordave  Acetominophen is an antipyretic and analgesic, but it is not antiinflammatory, so it wouldn't be useful for Niacin induced flushing. (See sketchy pharm for NSAIDs) +3
meja2  Acetiminophen mainly inhibits COX-2, thus would lead to inhibition of production of Leukotrienes, and more prostaglandins will be made from arachidonic acid only getting up by COX-1 [ I remember this by using its name, Ace-two-minophen for COX-2] +
fatboyslim  Maybe aspirin is chosen over acetaminophen because aspirin irreversibly inhibits COX +

COX-3, a splice variant of COX-1, has been suggested to be the site of action of paracetamol, but genomic and kinetic analysis indicates that this selective interaction is unlikely to be clinically relevant. There is considerable evidence that the analgesic effect of paracetamol is central and is due to activation of descending serotonergic pathways, but its primary site of action may still be inhibition of PG synthesis. The action of paracetamol at a molecular level is unclear but could be related to the production of reactive metabolites by the peroxidase function of COX-2, which could deplete glutathione, a cofactor of enzymes such as PGE synthase.

https://journals.lww.com/americantherapeutics/Abstract/2005/01000/Mechanism_of_Action_of_Paracetamol.8.aspx

But mainly, Acetominophen is an antipyretic and analgesic, but it is not antiinflammatory, so it wouldn't be useful for Niacin induced flushing.


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submitted by kungfupanda(5)
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Acetaminophen acts by inhibiting the COX-3 in the CNS and hence decreasing the body temperature, but not on the peripheral COX-1 & 2. hence, Aspirin is the better choice

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