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Cholinomimetics 2


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What are cholinomimetic drugs?
They mimic parasympathetic activity "rest/digest".
Muscarinic agonists
Direct acting muscarinic agonist agents
Direct acting muscarinic agonist agents MOA
Bind to and activate muscarinic receptors
Heart --> decrease HR
Blood vessels --> vasodilation (via NO)
Ciliary muscle --> contraction/near vision
Irish sphincter --> miosis
GI tract --> increase activity
Bladder --> micturation
What would be the problem with using ACh as a drug?
Too nonspecific and very rapidly hydrolyzed by AChE and pseudo AChE
What are the therapeutic uses of Bethanechol?
Postoperative abdominal distension and urinary retention
What are the therapeutic uses of Pilocarpine?
Sjogren's syndrome
Radiation induced dry mouth
What effect does muscarnic receptor activation have in teh eye?
Contract ciliary muscle
Contract iris sphincter--miosis
How is Pilocarpine used?
For radiation of cancer in head or neck or for Sjogren's syndrome --> decreased salivary secretion --> Pilocarpine --> activate M receptor --> increased salivation
What is Cevimeline used for?
Newer drug for Sjogren's syndrome (longer lasting)
What is Carbachol used for?
It is the 2nd line drug after Pilocarpine in the treatment of glaucoma.
What is Muscarine?
It is NOT a drug and is present in Inocybe and Clitocybe mushrooms; mushroom poisoning (mycetism)
What symptoms might you expect to see in a person who has mushroom poisoning from Inocybe mushrooms?
Adverse effects of muscarinic agonists
Direct acting muscarinic agonist

Adverse Effects?
Intestinal cramps/NVD
Increased gastric acid secretion
Reflex tachycardia
Difficulty breathing/asthma attack
How does muscarine and barorecptors work together?
Muscarine --> M3 --> decreased BP --> baroreceptor --> CNS --> increased HR and force of contraction
What are the adverse effects of direct acting muscarinic agonists on the eye?
Contract cilicary muscle --> lens rounds out --> near vision (spasm of accomodation--blurry)
Contract iris sphincter --> miosis
Indirect acting cholinomimetics

Reversible AChE inhibitor agents?
"Stigmine" and "riums"
Edrophonium + Atropine
Indirect acting cholinomimetics

Reversible AChE inhibitor agents that work in CNS?
Reversible AChE inhibitors MOA
Slows down the hydrolysis of ACh by AChE.
What happens to acetylcholine in the presence of neostigmine?
Neo binds to enzyme and ACh can't hydrolyze --> prolonged activity of ACh at receptor
Where is the site of action of physostigmine?
All cholinergic synapses--not very specific.
What are the therapeutic uses of physostigmine?
Treatment of glaucoma
Reverses antimuscarinic effects from plants that contain muscarinic blockers and drugs that have antimuscarinic effects.
Advantage: Lipid soluble
What are the therapeutic uses of neostigmine and pyridostigmine?
Postoperative urinary retention and abdominal distention (Neo)
Myasthenia Gravis (both)
What other agent can be used to treat postoperative abdominal distention and urinary retention?
How can we increase muscle strenth in patients with MG?
Increase the concentration of ACh in the NMJ --> increased muscle strength
What is the duration of action of Neostigmine?
2 to 4 hours
What is the duration of action of Pyridostigmine?
3 to 6 hours
What is Edrophonium?
Analog of neostigmine
Less potent
Shorter acting (3-4 minutes)
IV only
What are the therapeutic uses of edrophonium?
Diagnostic test for MG
Pt is weak --> give edrophonium --> improved muscle strength for 3-5 min.
What are the other therapeutic uses of edrophonium?
Assesses the adequacy of treatment with neo

Differentiates between a myasthenic crisis and a cholinergic crisis
How can one tell if the Neostigmine dose is too high?
Pt on neo --> weak --> give edrophonium --> decrease or no change in muscle strength --> Neo dose is too high
How can one tell if the Neo dose is too low?
Pt on neo --> weak --> give edrophonium --> increase in muscle strength --> neo dose is too low
How can too much neo produce muscle weakness?
There is no time for muscle cells to repolarize (Depolarization blockade)
What centrally acting reversible AChE inhibitors treat Alzheimer's Disease (AD)?
What is the difference in the drugs that treat AD?
All drugs produce a similar improvement in cognitive function. The biggest difference is in the dosing and side effects.
Tacrine for AD
Many side effects (especially GI and hepatotoxic)
Donepezil for AD
Least GI side effects, 1 X d dosing
Galantamine for AD
Middle GI side effects, 1 x d dosing
Most GI side effects, 2 X d dosing
What is the newest drug for AD?
Memantine which is an NMDA antagonist
What is carbamate cholinesterase inhibitors used for?
Garden insecticides--low dermal absorption

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