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Mechanism of Drug Action (Drugs) > Cholinergic transmission > Flashcards

Cholinergic transmission Flashcards

1
Q

What are the major processes that can be affected by drugs during cholinergic transmission?

A
  1. ACh synthesis
  2. ACh release
  3. ACh receptor binding
  4. ACh breakdown
  5. Breakdown product re-uptake
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2
Q

Which drugs affect ACh systhesis?

A

Triethylcholine: Competitive antagonist for choline acetyltransferase (CAT)

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3
Q

Which drugs affect ACh vesicular transport?

A

Vesamicol: Reversibly (but non-competitively) inhibits VAChT and prevents ACh loading into vesicles. Inhibits ACh release.

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4
Q

Which drugs affect ACh release?

A
  1. Botulinum toxin: Several isoforms all cut SNARE complex at different sites. Inhibits ACh release.
  2. Tetanus toxin: Degrades synpatobrevin. Inhibits ACh release.
  3. α-Latrotoxin: Causes massive uncontrolled discharge of ACh from nerve terminals and depletes ACh. Inhibits ACh release.
  4. β-bungarotoxin: Causes activation of phospholipase A2, leading to destruction of pre-synaptic nerve terminal. Inhibits ACh release.
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5
Q

Why does repeated use of botox result in decline in activity?

A

Botox is antigenic and neutralising antibodies eventually develop

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6
Q

Which drugs affect ACh re-uptake?

A

Hemicholinium: Inhibits Na+-dependent choline transporters (ChT) and thus inhibits choline re-uptake. This decreases amount of choline available for ACh synthesis and thus decreases ACh availability. Inhibits ACh release.

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7
Q

Which types of drugs affect ACh receptors?

A
  1. Neuromuscular-blocking drugs (nicotinic receptor antagonists)
  2. Ganglion stimulating/blocking drugs
  3. Muscarinic receptor agonists/antagonists
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8
Q

What are the types of neuromusclular-blocking drugs?

A
  1. Depolarising blocking agents
  2. Non-depolarising blocking agents
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9
Q

What are the depolarising blocking drugs?

A
  1. Suxamethonium
  2. Decamethonium
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10
Q

What is the mechanism of action of non-depolarising NMJ blockers?

A

All non-depolarising drugs are competitive antagonists of nAChRs (but more selective for N1).

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11
Q

What are the non-depolarising blocking drugs?

A
  • Clinically significant compounds include:
    1. Pancuronium
    2. Vecuronium
    3. Atracurium
    4. Mivacurium
  • Clinically insignificant compounds include:
    1. Curare
    2. D-tubocurarine
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12
Q

What is a non-reversible NMJ blocker?

A

α-bungarotoxin: Blocks nAChRs irreversibly in NMJ

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13
Q

What is the mechanism of action of ganglion-stimulating drugs?

A

nAChR agonists that bind selectively to N2 receptors in parasympathetic ganglia.

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14
Q

What are the ganglion stimulating drugs?

A
  1. Nicotine
  2. Lobeline
  3. Epibatidine
  4. Varenicline (clinically used to aid in nicotine withdrawal)
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15
Q

What is the mechanism of action of ganglion-blocking drugs?

A

All ganglion bocking drugs are nAChR antagonists specific for N2 ACh receptors.

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16
Q

What are the gangion blocking drugs?

A
  1. Hexamethonium
  2. Trimethapan
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17
Q

What is the clinical significance of trimethapan?

A

Lowers BP to minimise bleeding during surgery

18
Q

What are the classes of muscarinic agonists?

A
  1. Choline esters
  2. Cholinomimetic alkaloids
19
Q

What are examples of choline esters?

A
  • Acetylcholine
  • Methacholine
  • Carbachol
  • Bethanechol
20
Q

What are examples of cholinomimetic alkaloids?

A
  • Muscarine
  • Arecoline
  • Pilocarpine
  • Cevimeline
21
Q

What are the clinically used muscarinic agonists?

A
  1. Bethanechol
  2. Pilocarpine
  3. Cevimeline
22
Q

What is the clinical use of bethanichol?

A

Treatment of bladder/gastrointestinal hypotonia

23
Q

What is the clinical use of pilocarpine?

A

Treatment of glaucoma

24
Q

What is the clinical use of cevimeline?

A

Treatment of Sjögren’s syndrome

25
Q

What are the non-selective muscarinic antagonists?

A
  • Atropine
  • Hyoscine butylbromide (scopolamine)
  • Benzilylcholine
  • Tropicamide
  • Ipratropium
26
Q

What are the clinical uses of atropine?

A
  • Causes tachycardia (sinus bradycardia)
  • Inhibits GI mobility (diarrhoea)
  • [Low dose] Inhibits exocrine secretions (sweat, saliva, lacrimal…)
  • Used to reduce secretions in airways during surgery
  • Reduces GI and bladder spasms.
27
Q

What are the clinical uses of tropicamide/cyclopentolate?

A

Causes pupil dilation

28
Q

What are the clinical uses of scopolamine?

A
  • Prevents motion sickness
  • Relaxes gut muscles during endoscopy
29
Q

What are the clinical uses of ipratropium/tiotropium?

A

Bronchodilation (asthma/COPD)

30
Q

What are the M1 selective antagonists?

A

Pirenzepine

31
Q

What are the clinical uses of M1 antagonists?

A

Reduces gastric secretion and is used to treat gastric ulcers

32
Q

What are the clinical uses of pirenzepine?

A

Reduces gastric acid secreton (GORD & peptic ulcers)

33
Q

What are the M2 selective antagonists?

A

Tripitramine

34
Q

What are examples of M3 selective antagonists?

A

Darifenacin

35
Q

What are the clinical uses of M3-selective antagonists?

A

Relaxation of bladder (reduces urge for micturition)

36
Q

What are the classes of anticholinesterase drugs?

A
  1. Short-acting (non-covalent)
  2. Intermediate-acting (covalent)
  3. Irreversible (covalent)
37
Q

What are the short-acting (non-covalent) anticholinesterases?

A
  • Edrophonium: Diagnosis of myasthenia gravis
  • Tacrine: Treatment of Alzheimer’s disease
  • Donepezil: Treatment of Alzheimer’s disease
38
Q

What are the intermediate-acting (covalent) anticholinesterases?

A
  • Neostigmine:
    1. Intravenous → Reverses neuromuscular block
    2. Oral → Treatment of myasthenia gravis
  • Pyriostigmine: Treatment of myasthenia gravis
  • Physostigmine: Glaucoma (topical)
39
Q

What are the irreversible (covalent) anticholinesterases?

A
  • Echothiophate: Treatment of glaucoma
  • Dyflos: Treatment of glaucoma
  • Malathion: Treatment of headlice
40
Q

What are antidotes for organophosphate poisoning?

A
  • Atropine: Counteracts systemic effects
  • Pralidoxime (2-PAM): Reactivates AChE by dephosphorylating Ser203

Mechanism of Drug Action (Drugs) (26 decks)

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