Question

The short acting anticholinesterase drug is: 

• A. Physostigmine
• B. Edrophonium
• C. Ecothiophate
• D. Neostigmine

Answer 1

The Correct Option is B

The question asks for the identification of a short-acting anticholinesterase drug among the given options. To solve this, we need to understand what each drug does and determine which one fits the category of short-acting.

Anticholinesterase drugs work by inhibiting the enzyme acetylcholinesterase, which breaks down acetylcholine in the synaptic cleft. By inhibiting this enzyme, these drugs increase the amount of acetylcholine in the synaptic cleft, enhancing cholinergic transmission.

Let's examine each option provided:

1. Physostigmine: This is an intermediate-acting anticholinesterase agent. It is commonly used to treat glaucoma and certain types of poisoning, but it is not the shortest acting one.
2. Edrophonium: This is a short-acting anticholinesterase drug. It is primarily used in the diagnosis of myasthenia gravis (Tensilon test) because of its rapid onset and brief duration of action.
3. Ecothiophate: This is a long-acting anticholinesterase. It is an organophosphate compound used mainly in the treatment of glaucoma. It is not short-acting.
4. Neostigmine: Similar to Physostigmine, Neostigmine is an intermediate-acting agent used in the management of myasthenia gravis and as a reversal agent for neuromuscular blockade after surgery. It is not the shortest acting.

Based on the above analysis, the correct answer is Edrophonium, which is known for its short duration of action.

Conclusion: Edrophonium is the short-acting anticholinesterase drug among the given options.

Answer 2

The question asks which of these anticholinesterase drugs acts for the shortest time. The duration depends on how each drug binds to the enzyme acetylcholinesterase, so let's look at the binding mechanism of each.

1. Physostigmine: This drug forms a carbamylated bond with the enzyme that breaks down slowly, giving it an intermediate duration of action lasting a few hours. Being a tertiary amine, it can also cross the blood brain barrier.
2. Edrophonium: This drug attaches to the active site of acetylcholinesterase only through weak, reversible interactions such as electrostatic attraction and hydrogen bonding, without forming any lasting covalent bond. Because of this loose binding, it separates from the enzyme within minutes, giving it the shortest duration among these drugs.
3. Ecothiophate: This is an organophosphate that binds the enzyme through a bond that barely breaks down on its own, making the inhibition essentially irreversible and the drug's effect last for days to weeks, the longest of the four.
4. Neostigmine: Like physostigmine, this drug forms a carbamylated enzyme complex with an intermediate duration, commonly used to reverse muscle relaxants after surgery rather than for quick diagnostic use.

Because edrophonium binds only briefly and reversibly, without any covalent step, it separates from the enzyme far faster than the others, making it the shortest acting of the four.

Therefore, the correct answer is Edrophonium.