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Pharmacology: WEEK 7 Muscarinic Agonists & Antagonists

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created 3 years ago by Husky_Murse
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updated 3 years ago by Husky_Murse

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1

This prototypical muscarinic agonist is used primarily to relieve urinary retention, but also GERD (increase gastric emptying), ileus (increase bowel motility), and post-op ABD distention

Bethanechol

2

This type of poisoning results in profuse salivation, tearing, visual disturbances, bronchospasm, diarrhea, bradycardia, and hypotension

Muscarinic agonist poisoning

3

Treatment for muscarinic agonist poisoning

Atropine

4

Prototypical muscarinic antagonist (anticholinergic) drug

Atropine

5

Another term for muscarinic antagonist

Anticholinergic

6

Atropine acts at muscarinic cholinergic receptor sites to induce these actions:

1. Increases HR

2. Reduce sweat/salivation/bronchial & GI secretion

3. Intestinal/bronchial relaxation

4. Causes urinary retention (relaxes bladder & contracts trigone/sphincter)

5. Causes mydriasis (pupil dilation)

6. CNS excitation

7

Some applications of anticholinergic drugs

-Preanesthetics

-Opthalmic exams (mydriasis - pupil dilation)

-Reversal of bradycardia

-TX of overactive bladder

-Management of muscarinic agonist poisoning

8

Classic adverse effects of anticholinergic drugs

-Dry mouth

-Blurred vision/photophobia

-Tachycardia

-Urinary retention

-Constipation

-Decreased sweating

9

This muscarinic receptor subtype is located in the CNS & salivary glands

M1

10

This muscarinic receptor subtype is located in the heart

M2

11

This muscarinic receptor subtype is located in the bladder, GI smooth muscle, & eyes (along with salivary glands)

M3

12

Low doses of atropine will produce anticholinergic effects in these areas

-Salivary glands (reduced)

-Sweat glands (reduced)

-Bronchial glands (reduced)

13

Moderate doses of atropine will produce anticholinergic effects in these areas

-Heart (increased rate)

-Eye (mydriasis, blurred vision)

-Urinary tract (retention)

14

High doses of atropine will produce anticholinergic effects in these areas

-Stomach/intestine (reduced acid secretion & tone)

-Lung (bronchial dilation)

15

Stimulation of parasympathetic & sympathetic postganglionic nerves & release of epi from adrenal medulla; type of receptor that comprises all preganglionic neurons

Nn

16

All parasympathetic target organs are innervated by this receptor type

Muscarinic (M)

17

Contraction of skeletal muscle; type of receptor in the somatic motor system that innervates skeletal muscle

Nm

18

This type of cholinergic agent binds to cholinergic receptors & "mimics", causing stimulation

Direct Acting (i.e. Bethanechol)

19

This type of cholinergic agent inhibits acetylcholinesterase, resulting in more ACh available for enhanced cholinergic (parasympathetic) response

Indirect Acting

20

Sources of muscarinic poisoning

-Direct Acting muscarinic agonists (Bethanechol)

-Cholinesterase inhibitors

-Mushrooms (i.e. Jack o' Lantern mushrooms)

21

Some pharmacological effects of muscarinic agonists (i.e. Bethanechol)

-Decrease HR/contractility

-Stimulate GI

-Contract bladder

-Stimulate salivation

22

Direct-acting muscarinic agonist

Bethanechol

23

Adverse effects of Bethanechol

-Salivation

-Diaphoresis

-GI hyperactivity

-Headache

-Colic

24

Drug that blocks action of ACh muscarinic receptors

Atropine

25

Uses of atropine include:

-Eye D/O (induces mydriasis for exam)

-TX bradycardia

-TX intestinal hypermotility

-TX muscarinic agonist poisoning

-TX asthma (induces bronchodilation)

-Refractory symptoms of PUD

26

Muscarinic antagonist used to treat overactive bladder

Oxybutynin

27

2 basic categories of cholinesterase inhibitors

Reversible & irreversible

28

This acronym is associated with remembering the adverse effects associated with cholinesterase inhibitors (i.e. parasympathetic system is let loose!)

SLUDGE:

-Salivation

-Lacrimation

-Urinary incontinence

-Diarrhea

-GI cramps

-Emesis

29

Reversible cholinesterase inhibitors, such as neostigmine, have these 2 clinical applications

-Myasthenia Gravis

-Reverse neuromuscular blocking agents

30

Autoimmune neuromuscular disease characterized by weakness & fatigue of muscles

Myasthenia Gravis

31

Pharmacological treatment for Myasthenia Crisis

Neostigmine (reversible cholinesterase inhibitor)

32

Longer acting; commonly found in insecticides; used primarily to treat glaucoma

Irreversible cholinesterase inhibitors

33

2nd leading cause of blindness; increased intraocular pressure & optic nerve atrophy

Glaucoma

34

Caused by overdose of cholinesterase inhibitor

Cholinergic Crisis

35

Treatment for Cholinergic Crisis (OD of cholinesterase inhibitor)

Atropine

36

This drug should be readily available for clients taking irreversible drugs

Atropine

37

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. What pharmacological TX would apply in his case?

Bethanechol (direct-acting muscarinic agonist)

38

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. You're considering Bethanechol for his urinary retention. You find out he's concurrently being treated for asthma. Is Bethanechol a good choice in light of this?

No - will cause bronchoconstriction (parasympathetic response)

39

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. You're considering Bethanechol for his urinary retention. You read that he had an obstructed urethra 5 years ago. Is Bethanechol a good choice in light of this?

No - may cause further damage to urethra

40

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. You're considering Bethanechol for his urinary retention. Your assessment reveals he's being treated with a vasodilator for HTN. Is Bethanechol still a good choice in light of this new information?

No - additive vasodilation due to cholinergic effects on blood vessels

41

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. You're considering Bethanechol for his urinary retention. You read he has a HX of constipation with no other GI pathology. Is Bethanechol still a good choice for his retention?

Yes - it may actually help with his constipation, too (cholinergic effects on GI system)

42

Melvin is a 62-year-old male post-op knee SX patient who hasn't voided in 18 hours. You're considering Bethanechol for his urinary retention. If Melvin reported the following symptoms r/t taking Bethanechol, would they be expected or unexpected?

1. Excessive salivation

2. Tachycardia

3. Mydriasis

4. Orthostatic hypotension

1. Expected

2. Unexpected (sympathetic)

3. Unexpected (sympathetic - atropine)

4. Expected

43

There is concern that there are pathologic changes in the vasculature of your patient’s eyes. You are assisting in an eye exam on your patient.

1. What class of drug will you likely use?

2. Will you likely give this drug systemic or local?

3. Your patient is leaving the clinic: What intervention may be helpful for your patient until the effects of the drug wear off?

1. Muscarinic antagonist - Atropine

2. Locally - reduce systemic effects

3. Sunglasses (photophobia r/t mydriasis caused by Atropine)

44

You go in to see your patient (Sheila) and she does not look well. You immediately get a set of vitals and note that her BP is 88/50 and her HR is 50. You notify your nurse who notifies the appropriate response team. Think muscarinic receptors and think HR: What class of drug/prototype drug will you want to give as a part of the pharmacologic intervention?

Muscarinic antagonist - Atropine

45

What does it mean if you are treating your patient with Atropine to decrease salivation versus treating your patient with Atropine to dilate bronchi?

Doses required to reduce salivation will be lower than those to required to dilate the bronchi ( we will likely see many anticholinergic side effects (involving eyes, gut, blood vessels etc) when using atropine to dilate bronchi)


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