NBME 20 Succinylcholine (NBME Answers)

Retired NBME 20 Answers

nbme20/Block 3/Question#47 (reveal difficulty score)
A 60-year-old woman has prolonged apnea ...
Succinylcholine 🔍 / 📺 / 🌳 / 📖
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submitted by ∗xxabi(293)

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The duration of action of Succinylcholine is determined by its metabolism by plasma cholinesterase. So if there is abnormal plasma cholinesterase (=psuedocholinesterase), it will lead to delayed metabolism of succinylcholine as well as mivacirum, heroin, and cocaine.

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athenathefirst So because there was a problem with cholinesterase then the only one would be affected is acetylcholine since it's metabolized by acetylcholine. +

athenathefirst *acetylcholine esterase (sorry meant that) +

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submitted by ∗niboonsh(409)

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https://www.youtube.com/watch?v=WGWFFN01qkA succinylcholine usually has v fast duration of action bcuz metabolized by plasma pseudocholinesterase. With atypical pseudocholinesterase, decreased metabolism of succinylcholine and thus causes a prolonged duration of action of succinylcholine ----> APNEA

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chandlerbas i love that mosquito and then SLAP +1

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submitted by ∗haozhier(23)

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From FA, succinylcholine can be reversed during phase 2 by cholinesterase inhibitor. Can someone explain if succinylcholine is metabolized by cholinesterase, how can we use cholinesterase inhibitors to reverse it?

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roseanneg I think what happens is that acetylcholinesterase inhibitors will start to increase acetylcholine in the synapse and that can now compete with succinylcholine. But then again, at phase 2, it says that there is desensitization to acetylcholine at phase II so idk. Also, note that succinylcholine is metabolized by PLASMA cholinesterase but is resistant to acetylcholinesterase. I'm not sure if that contributes to the reason. +

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submitted by thomas(3)

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Not sure about this, but it seems to me that this is referring to "pseudocholinesterase inhibitor deficiency. It's an enzyme defect that is triggered by NMJ blockers - succinylcholine or curare's.

https://en.wikipedia.org/wiki/Pseudocholinesterase_deficiency

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usmleuser007 I believe this question was stating that AchE activity was abnormal = it was not lowering the Ach activity. Which suggests that another ligand like Ach was being used. +

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