Short acting anticholinesterase is
**Core Concept**
Edrophonium is a short-acting anticholinesterase used in the diagnosis of myasthenia gravis. It works by inhibiting acetylcholinesterase, the enzyme responsible for breaking down acetylcholine in the synaptic cleft, thereby increasing the concentration and duration of acetylcholine's action on nicotinic receptors at the neuromuscular junction.
**Why the Correct Answer is Right**
Edrophonium's short duration of action is due to its rapid hydrolysis by pseudocholinesterase, an enzyme present in the plasma. This results in a brief increase in acetylcholine levels, which can be used to assess the response of patients with suspected myasthenia gravis. Edrophonium's action is terminated quickly, allowing for the assessment of muscle function without prolonged cholinergic effects.
**Why Each Wrong Option is Incorrect**
**Option A:** Physostigmine is a long-acting anticholinesterase, used to treat glaucoma and anticholinergic toxicity.
**Option B:** Pyridostigmine is a long-acting anticholinesterase, used in the management of myasthenia gravis.
**Option C:** Neostigmine is a long-acting anticholinesterase, used to reverse non-depolarizing neuromuscular blockade and treat myasthenia gravis.
**Clinical Pearl / High-Yield Fact**
Edrophonium's short duration of action makes it an ideal agent for the diagnosis of myasthenia gravis, as it allows for a rapid assessment of muscle function without prolonged cholinergic effects.
**Correct Answer: D. Edrophonium**