reversible cholinesterase inhibitors

Question 1

Name the 4 reversible cholinesterase inhibitors

Answer 1

Edrophonium, neostigmine, pyridostigmine, physostigmine

Question 2

What is the short acting reversible inhibitor and what is the mechanism of action?

Answer 2

Edrophonium - positive charge binds weakly to anionic site of AChE (simple competition) thus reducing ACh breakdown in synapse and potentiating neurotransmission

Question 3

What can be used to identify/diagnose myasthenia gravis muscle weakness?

Answer 3

Edrophonium. It’s action too short for therapeutic use.

Question 4

What is an adverse effect of edrophonium?

Answer 4

May exacerbate asthma. Unwanted parasympathetic actions can be reversed by atropine.

Question 5

What are the 2 long acting reversible inhibitors?

Answer 5

Neostigmine and pyridostigmine

Question 6

How does neostigmine act?

Answer 6

Reversible inhibition of acetylcholinesterase reduces breakdown of ACh at cholinergic nerve-endings, so potentiating transmitter action. Binds to both esteratic and anionic sites in the enzyme. The esterase is carbamylated.

Question 7

What is the clinical use of neostigmine (and pyridostigmine)?

Answer 7

Myasthenia gravis - increases time ACh is present in synapse and so increases likelihood of binding, increasing muscle response and decreasing muscle weakness. Reversal of non-depolarising neuromuscular block.

Question 8

What is the clinical use of physostigmine?

Answer 8

Gluacoma - decreases intra-ocular pressure by increasing parasympathetic synaptic transmission.

Question 9

How can neostigmine be used in the GI tract?

Answer 9

Enhances muscle tone