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Mechanism of Drug Action > Pharmacology of the Peripheral Neural Transmission (Drugs) > Flashcards

Pharmacology of the Peripheral Neural Transmission (Drugs) 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 break-down
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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. Aminoglycoside antibiotics (e.g. streptomycin, neomycin): Inhibits P-type Ca2+ channels that mediate Ca2+ entry into the pre-synaptic terminal. Inhibits ACh release.
  2. Botulinum toxin: Several isoforms all cut SNARE complex at different sites. Inhibits ACh release.
  3. Tetanus toxin: Degrades synpatobrevin. Inhibits ACh release.
  4. α-Latrotoxin: Causes massive uncontrolled discharge of ACh from nerve terminals and depletes ACh. Inhibits ACh release.
  5. β-bungarotoxin: Causes activation of phospholipase A2, leading to destruction of pre-synaptic nerve terminal. Inhibits ACh release.
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5
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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6
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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7
Q

What are the types of neuromusclular-blocking drugs?

A
  1. Depolarising blocking agents
  2. Non-depolarising blocking agents
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8
Q

What are the depolarising blocking drugs?

A

Suxamethonium: nAChR agonist that causes sustained depolarisation of the post-synaptic terminal and thus induces blocking of ACh action (phase I and II)

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9
Q

What are the non-depolarising blocking drugs?

A

All non-depolarising drugs are competitive antagonists of nAChRs (but more selective for N1). Clinically significant compounds include:

  1. Pancuronium
  2. Vecuronium
  3. Atracurium
  4. Mivacurium
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10
Q

What is a non-reversible NMJ blocker?

A
  • α-bungarotoxin: Blocks nAChRs irreversibly in NMJ
  • Decamethonium
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11
Q

What are the ganglion stimulating drugs?

A

nAChR agonists that bind selectively to N2 receptors in parasympathetic ganglia. Non-clinically used compounds include:

  1. Nicotine
  2. Lobeline

Clinically used compounds include:

  1. Epibatidine
  2. Varenicline
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12
Q

What are the gangion blocking drugs?

A

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

Non-clinically used: Hexamethonium

Few are in clinical use due to widespread side effects. Clinically used: Trimethapan (lowers BP to minimise bleeding during surgery)

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13
Q

What are the muscarinic agonists?

A
  1. Choline esters:
    - Acetylcholine
    - Methacholine
    - Carbachol
    - Bethanechol
  2. Cholinomimetic alkaloids:
    - Muscarine
    - Arecoline
    - Pilocarpine
    - Cevimeline
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14
Q

What are the clinically used muscarinic agonists?

A
  1. Bethanechol: Treatment of bladder/gastrointestinal hypotonia
  2. Pilocarpine: Treatment of glaucoma
  3. Cevimeline: Treatment of Sjögren’s syndrome
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15
Q

What are the muscarinic antagonists?

A
  1. M1 selective:
    - Pirenzepine: Treatment of peptic ulcers (reduces gastric acid secretion)
  2. M2 selective:
    - Tripitramine
  3. M3 selective (treatment of over-reactive bladder):
    - Oxybutynin
    - Tolterodine
    - Darifenacin
    - Solifenacin
  4. Non-selective:
    - Atropine: Used to reduce secretions in airways during surgery and reduces GI and bladder spasms.
    - Hyoscine butylbromide: Anti-spasmodic
    - Benzilylcholine
    - Tropicamide
    - Ipratropium
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16
Q

Which drugs affect acetylcholine breakdown?

A
  1. Short-acting (non-covalent):
    - Edrophonium: Diagnosis of myasthenia gravis
    - Tacrine: Treatment of Alzheimer’s disease
    - Donepezil: Treatment of Alzheimer’s disease
  2. Intermediate-acting (covalent):
  • Neostigmine:
    Intravenous → Reverses neuromuscular block
    Oral → Treatment of myasthenia gravis
  • Pyriostigmine: Treatment of myasthenia gravis
    3. Irreversible (covalent):
  • Echothiophate: Treatment of glaucoma
  • Dyflos: Treatment of glaucoma
  • Malathion: Treatment of headlice
17
Q

What are antidotes for organophosphate poisoning?

A
  • Atropine: Counteracts systemic effects
  • Pralidoxime (2-PAM): Reactivates AChE by dephosphorylating Ser203
18
Q

Which drugs affect noradrenaline synthesis?

A
  1. α-methyltyrosine (phaeochromocytoma): inhibits tyrosine hydroxylase
  2. Carbidopa (Parkinson’s): Inhibits DOPA decarboxylase (DDC)
  3. Disulfiram (Chronic alcoholism): Inhibits dopamin β-hydroxylase (DBH)
  4. α-Methyldopa (Hypertension): False transmitter and inhibits action of NA is several ways:
    - Inhibits DDC and DBH
    - Displaces NA from vesicles and causing MAO breakdown
    - Binds to pre-synpatic α2 receptors and inhibits NA release via feedback inhibition
19
Q

Which drugs block noradrenaline storage and release?

A
  1. Reserpine: Inhibits VMAT and thus NA uptake into vesicles
  2. Guanethidine: Possibly inhibits exocytosis of NA and displaces NA from vesicles
20
Q

What are the indirect sympathomimetics?

A
  • Tyramine (found in foods)
  • Ephedrine (nasal congestion)
  • Dextroamphetamine (narcolepsy & ADHD)
21
Q

Which drugs affect noradrenaline uptake?

A
  • Tricyclic antidepressants (e.g. imipramine): Inhibits NET (uptake 1)
  • Cocaine: Inhibits NET (uptake 1)
  • Steroid hormones (e.g. hydrocortisone): Inhibits EMT (uptake 2)
  • Normetnephrine: Inhibits EMT (uptake 2)
  • Phenoxybenzamine: Inhibits NET & EMT
22
Q

Which drugs selectively act on α1 adrenreceptors?

A

Agonists:

  1. Phenylephrine
  2. Oxymetazoline

Antagonists:

  1. Prazosin
23
Q

Which drugs selectively act on α2 adrenoreceptors?

A

Agonists:

  1. Clonidine
  2. Xylazine

Antagonists:

  1. Yohimbine
24
Q

Which drugs non-selectively act on α adrenoreceptors?

A

Agonists:

  1. Topical decongestants

Antagonists:

  1. Phenozybenzamine
  2. Phentolamine
25
Q

Which drugs selectively act on β1 adrenoreceptors?

A

Agonists:

  1. Dobutamine

Antagonists:

  1. Metoprolol
  2. Nebivolol
26
Q

Which drugs selectively act on β2 adrenoreceptors?

A

Agonists:

  1. Salbutamol
  2. Salmeterol
  3. Terbutaline
  4. Clenbuterol

Antagonists:

  1. Butoxamine
27
Q

Which drugs act selectively on β3 adrenoreceptors?

A

Agonists:

  1. Mirabegron
28
Q

Which drugs act non-selectively on β adrenoreceptors?

A

Agonists:

  1. Isopraline

Antagonists:

  1. Propanolol
  2. Alprenolol
29
Q

Which drugs act non-selectively on adrenoreceptors in general?

A

Agonists:

  1. Adrenaline
  2. Noradrenaline

Antagonists:

  1. Labetalol
  2. Carvedilol

Mechanism of Drug Action (28 decks)

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