Neostigmine antagonizes non–depolarizing blockade by all of the following mechanisms EXCEPT :
**Core Concept**
Neostigmine is a cholinesterase inhibitor that reverses non-depolarizing neuromuscular blockade by increasing the concentration of acetylcholine at the neuromuscular junction. This is achieved through the inhibition of acetylcholinesterase, the enzyme responsible for breaking down acetylcholine.
**Why the Correct Answer is Right**
Neostigmine increases the concentration of acetylcholine, which competes with non-depolarizing blockers for receptor sites on the muscle endplate. This competition leads to a decrease in the effectiveness of the non-depolarizing blockers, ultimately reversing the neuromuscular blockade. Additionally, neostigmine can also increase the release of acetylcholine from the motor nerve terminal, further contributing to the reversal of blockade.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not a correct mechanism of neostigmine action, but rather a potential side effect of neostigmine administration, such as bradycardia, which can occur due to increased parasympathetic tone.
**Option B:** This is a correct mechanism of neostigmine action, as it increases the concentration of acetylcholine at the neuromuscular junction, competing with non-depolarizing blockers for receptor sites.
**Option C:** This is a correct mechanism of neostigmine action, as it increases the release of acetylcholine from the motor nerve terminal, further contributing to the reversal of blockade.
**Clinical Pearl / High-Yield Fact**
Neostigmine is a reversible cholinesterase inhibitor, meaning that its effects are short-lived and it can be administered repeatedly as needed to reverse non-depolarizing neuromuscular blockade.
**Correct Answer:** A.