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Pharmacology > Lecture 12: Cholinergic Agonists > Flashcards

Lecture 12: Cholinergic Agonists Flashcards

1
Q

Describe cholinergic transmission

A
  1. ACh synthesized from choline and acetyl CoA
  2. Stored in vesicles
  3. Depolarization and influx Ca2+ causes vesicular fusion and release
  4. Stimulates cholinergic or muscarinic receptors
  5. Alters target cell function
  6. Hydrolyzed by AChE and endocytosed
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2
Q

What receptor does Bethanecol target

A

M receptor agonist

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3
Q

T or F: all uses for Bethanecol are extra label

A

True

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4
Q

What are the indications for use for Bethanecol

A
  1. GI and bladder atony in cats, dogs and maybe horses
  2. Cecal displacement in cows
  3. Equine gastric ulcer syndrome
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5
Q

Why might you not want to use bethanecol to treat cecal displacement in cows

A

Requires compounding

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6
Q

What are the pharmacodynamics of bethanecol

A

Affect GI and urinary systems most strongly

M receptor agonist- direct cholinergic agonist

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7
Q

How is Bethanecol administered in dogs and large animals

A

Dogs- PO
Large animals- SQ

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8
Q

What are the adverse effects of bethanecol

A

Overextension of the therapeutic effect—-> too much GI and bladder motility

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9
Q

What can bethanecol cause in horses

A

Colic

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10
Q

What are some contraindications for bethanecol

A
  1. GI obstruction
  2. Blocked urethra
  3. Gastric ulcers in small mammals
  4. Hyperthyroidism
  5. Bradycardia, hypotension, vagal nerve dysfunction
  6. Asthma
    7.epilepsy
  7. Recent GI surgery
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11
Q

Why is bethanecol only contraindicated in small animals with GI ulcers but is used as a treatment for large animals

A

Large animals gastric pH is much higher and the purpose of increased GI motility is to remove the gastric acid. In small mammals it would just make it worse

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12
Q

Why is bethanecol contraindicated in hyperthyroid patients

A

HR for hyperthyroid patients is so high that an abrupt change can induce atrial fibrillation

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13
Q

what do M receptor agonists do to the respiratory system

A

Stimulate PNS system so bronchoconstriction

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14
Q

Why do you not want to use bethanecol after a recent GI surgery

A

Rip sutures

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15
Q

How do indirect cholingeric agonists like neostigmine and pyridostigmine work

A

Competitive antagonism with acetylcholine for acetylcholinesterase, so they tie up AChE so it will leave ACh alone and can increase its time in cleft

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16
Q

What are some etiologies for myasthenia gravis

A
  1. Autoimmune attack of NM receptors
  2. Paraneoplastic- thymoma
  3. Treatment with methinazole in cats with hyperthyroidism
  4. Congenital
17
Q

What are the labeled indications for neostigmine

A

GI or bladder atony especially following surgery

Labeled for use in sheep, swine, cattle and horses

18
Q

What is the extra label use of neostigmine

A

Diagnosis and treatment of myasthenia and reversal fo NMJ blockade (atracurium)

19
Q

What is the absorption of neostigmine

A

Administered IV so 100%

20
Q

What is the distribution of neostigmine

A

0.13l/kg in labs

21
Q

What is the metabolism for neostigmine

A

Plasma cholinesterases and liver

22
Q

What is the elimination for neostigmine and t1/2

A

Urinary, t 1/2- 40 seconds

23
Q

What is an adverse effect of neostigmine

A

Cholinergic crisis

24
Q

What happens during a cholingeric crisis

A

Decrease BP, decrease HR, bronchoconstriction

25
Q

What is the labeled used for pyridostigmine bromide

A

Treatment of myasthenia gravis in dog

26
Q

Why is pyridostigmine bromide extra label use in cats

A

Because myasthenia like symptoms are usually a result of treatment with methinazole for hyperthyroidism so take patient off drug and symptoms resolve

27
Q

What is the absorption of pyridostigmine bromide

A

Not well characterized

28
Q

What is the distribution of pyridostigmine bromide

A

1L/kg in labs

29
Q

What is the metabolism of pyridostigmine bromide

A

Plasma cholinesterases and liver

30
Q

What is the elimination and t1/2 for pyridostigmine bromide

A

Urinary, t1/2-2 minutes

31
Q

What are the adverse effects of pyridostigmine bromide

A
  1. Tolerance due to downregulation of Nm receptors so must increase dose
  2. Intussusception- usually a result of high doses
32
Q

What do cholinergic agonists do to heart, lungs, GI, eyes, GU and vasculature

A

Heart: decrease HR
Lungs: bronchoconstriction
GI: increase motility
Eyes: miosis, tear formation, decrease IOP
GU: relax sphincter and contract fundus to promote urination
Vasculature: direct acting agonist act on M receptors in vasculature and decrease BP via vasodilation

Pharmacology (14 decks)

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