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A. General Pharmacology > 2. Cholinergics & anticholinergics > Flashcards

2. Cholinergics & anticholinergics Flashcards

1
Q

Types of cholinergic receptors

A 
1. Muscarinic: 
M1: stomach, CNS (nausea and vomiting pathways) 
M2: heart, CNS
M3: lungs, glands, GI tract, CNS
M4, M5: CNS
  1. Nicotinic:
    N1 or Nm: skeletal muscle
    N2 or Nn: ganglion, CNS
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2
Q

Common adverse effects of cholinergic agonists

A

diarrhoea, diaphoresis, miosis, nausea, urinary urgency

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3
Q

General contraindications of cholinergic drugs

A
  1. asthma (they cause bronchoconstriction)

2. peptic ulcer (they enhance gastric acid secretion)

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4
Q

Types of direct cholinergic drugs

A

Muscarinic: pilocarpine, bethanechol
Nicotinic: nicotine, varenicline (partial agonist)
Muscarinic & nicotinic: acetylcholine

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5
Q

Does acetylcholine cross membranes or BBB?

A

No, it is a quaternary ammonium

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6
Q

MOA and uses of pilocarpine

A
  1. Alkaloid nonselective muscarinic acetylcholine receptor agonist
  2. M3 receptor activation
  3. Treatment of glaucoma (both narrow- and wide-angle) by freeing entrance to Schlemm’ canal for narrow-angle and enhancing tone of the trabecular meshwork for wide-angle
  4. Treatment of xerostomia (dry mouth) by promoting salivation
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7
Q

Adverse / side effects of pilocarpine

A
  1. topical ophthalmic administration → minimal systemic absorption but local stinging and irritation
  2. oral administration → sweating, blurred vision, and other cholinergic adverse effects + worsens asthma and COPD
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8
Q

MOA and uses of bethanechol

A
  1. quaternary choline ester muscarinic acetylcholine receptor agonist (M3)
    - GU: increase detrusor tone and decrease outlet resistance of internal sphincter
    - GI: increase motility and secretion
    - weak agonist at M2 → minimal cardiac effects
    - crosses BBB poorly → minimal CNS effects
  2. Treatment of gastric atony by increasing motility and secretion in the GI
  3. Treatment of urinary retention by increasing detrusor tone and decreasing outlet resistance of internal sphincter
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9
Q

Adverse / side effects of bethanechol

A
  1. pulmonary: bronchoconstriction, increase secretions
  2. GI: nausea, vomiting cramps and diarrhoea
  3. ophthalmic: miosis

Contraindicated in asthma!

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10
Q

MOA & uses of nicotine

A
  1. Nm (neuromuscular) nicotinic acetylcholine receptor agonist
    - Skeletal muscle contraction, fasciculations, spasms
    - High dose → depolarising blockade
  2. Nn (neuronal) nicotinic acetylcholine receptor agonist
    - Adrenal medulla: adrenaline release
    - Cardiac: increase HR
    - Vascular: peripheral vasoconstriction
    - GI: increase gut motility, increase secretions
    - Carotid bodies: increase RR
    - medullary emetic chemoreceptors: nausea & vomiting
  3. Clinical uses: aid to smoking cessation
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11
Q

Adverse / side effects of nicotine

A
  1. dependence due to activation of brain dopaminergic reward pathways
  2. low dose: increase HR, RR, BP, decrease appetite
  3. high dose: medullary depression, bradycardia, neuromuscular blockade
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12
Q

MOA & uses of varenicline

A
  1. partial nicotinic agonist

2. highly effective in smoking cessation

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13
Q

Adverse / side effects of varenicline

A

associated with psychiatric symptoms, including suicide ideation

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14
Q

Types of indirect cholinergic drugs

A
  1. Acetylcholinesterase (AChE) inhibitors

2. Low does nicotine

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15
Q

MOA of AChE inhibitors

A

Increase the availability of acetylcholine

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16
Q

Classification of AChE inhibitors

A
  1. Reversible
    - Short acting: Edrophonium
    - Long-acting: Neostigmine, Pyridostigmine, Physostigmine (carbamates) + Donepezil
  2. Irreversible or poorly reversible
    - Very long-acting: Sarin, malathion, parathion
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17
Q

MOA and uses of donepezil / physostigmine

A
  1. noncovalent acetylcholine esterase inhibitor
  2. crosses BBB readily (in contrast to neostigmine)
  3. physostigmine: carbamate AChE inhibitor that is tertiary amine → crosses BBB readily
  4. clinical use for donepezil → produces modest cognitive improvement → Alzheimer’s disease
  5. clinical use for physostigmine → antidote for atropine poisoning
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18
Q

Adverse/side effects of donepezil / physostigmine

A

diarrhoea, nausea, vomiting and other common cholinergic side effects

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19
Q

MOA & uses of neostigmine

A
  1. carbamate inhibitor of AChE
  2. M3: contracts GI and GU smooth muscles, decreases sphincter tone and increase secretions
  3. clinical uses for neostigmine:
    - reversal of nondepolarising neuromuscular blockade
    - myasthenia graves
    - increase GI motility on post op or neurogenic ileus
    - treatment of urinary retention secondary to bladder atony
20
Q

Adverse/side effects of neostigmine

A
  1. peripheral cholinergic adverse effects: diarrhoea, sweating, urinary urgency
  2. quaternary carbamate: poor absorption, do not penetrate into CSF
21
Q

MOA of sarin, parathion, malathion

A

potent suicide inhibitor of AChE → increase ACh at NM and neuronal synapses

22
Q

Clinical manifestation of sarin acute poisoning

A 
Cholinergic crisis:
SLUD
S - Salivation 
L - Lacrimation 
U - Urination 
D - Defecation

+ abdominal cramps, miosis, hypotension, bradycardia

23
Q

Antidote for sarin acute poisoning

A
  1. Cholinesterase regenerator: Pralidoxime

2. mACh receptor blockers: Atropine

24
Q

MOA / uses for Pralidoxime

A
  1. cholinesterase regenerator
  2. higher affinity for phosphate than AChE
  3. clinical use: acute treatment of organophosphate poisoning
25
Q

Limitations of pralidoxime

A
  1. Must be administered within a few hours before “ageing” occurs
  2. Only effective in organophosphate poisoning
  3. Not effective if AChE is carbamylated (e.g. by neostigmine)
26
Q

Types of direct anticholinergic drugs

A
  1. Receptor antagonists:
    - Muscarininc: atropine, benzatropine, scopolamine, ipratropium, oxybutynin
    - Non-depolarising neuromuscular blocking agents (NMBAs)
  2. Ganglionic blockers:
    High dose nicotine
27
Q

Adverse effects of anticholinergic drugs

A

blurred vision, confusion, mydriasis, constipation, urinary retention

28
Q

MOA / uses of atropine

A
  1. nonselective muscarinic acetylcholine receptor antagonist
    - M1 block → decrease gastric acid secretion; CNS confusion/delirium
    - M2 block → increase HR
    - M3 block → decrease saliva, decrease bronchial secretions; decrease sweat; mydriasis; cycloplegia; inhibit micturition; decrease GI tone and motility; decrease GI secretions
    - M4/M5 block → contribute to CNS effects
  2. treatment of bradycardia
  3. treatment of anti cholinesterase overdose
  4. GI antimotility agent to treat diarrhoea (with diphenoxylate)
  5. for ophthalmic examination - cycloplegia and mydriasis
29
Q

Adverse / side effects / contraindications of atropine

A

“red as a beet, blind as a bat, dry as a bone, hot as a hare, and mad as a hatter”

  1. red as a beet → superficial vasodilation
  2. blind as a bat → blurred vision
  3. dry as a bone → decrease secretions
  4. hot as a hare → hyperthermia (decrease sweat)
  5. mad as a hatter → delirium and hallucinations

Contraindicated in narrow-angle glaucoma!

30
Q

MOA / uses of benzatropine

A
  1. Nonselective muscarinic acetylcholine receptor antagonist
  2. Tertiary amine alkaloid → crosses the BBB better and has stronger CNS effects
  3. dopaminergic-cholinergic balance in striatum
  4. treatment of Parkinson’s disease and Parkinsonism
31
Q

Adverse / side effects / contraindications of benzatropine

A

hyperthermia (decrease sweat), glaucoma, urinary retention, dry mouth, constipation, blurred vision, sedation, amnesia, delirium, hallucinations

Contraindicated in narrow-angle glaucoma!

32
Q

MOA / uses of scopolamine

A
  1. Nonselective muscarinic acetylcholine receptor antagonist
    - M3 block → inhibits secretions and relaxes smooth muscles
    - M2 block → tachycardia
    - CNS → antiemetic and amnesic
  2. treatment of motion sickness, urinary incontinence, adjunct for anaesthesia (amnesia, decrease secretions, decrease nausea)
33
Q

Adverse / side effects / contraindications of scopolamine

A

dry mouth, constipation, urinary retention, blurred vision, sedation, glaucoma

Contraindicated in narrow-angle glaucoma!

34
Q

MOA / uses of ipratropium

A
  1. Nonselective muscarinic acetylcholine receptor antagonist
    - M3 block → decrease bronchoconstriction and decrease bronchial secretions
  2. Quaternary amine → poorly absorbed systematically and minimal CNS effects
  3. treatment of COPD (1st line therapy) & asthma (via inhalation as a 2nd line therapy)
35
Q

Side effects of ipratropium

A
  1. minimal due to poor systemic absorption
  2. dry mouth
  3. sedation (administration with bromide which can cross BBB to cause sedation)
  4. bradycardia (rarely)
36
Q

MOA / uses of oxybutynin

A
  1. Nonselective muscarinic acetylcholine receptor antagonist
    - M3 block → relaxes smooth muscle walls, increase sphincter tone and decrease secretions
    - M1 block → decease gastric acid production (via action on enterochromaffin-like cells)
  2. tertiary amine
  3. treatment for urinary incontinence
  4. reduction of gastric acid secretion and treatment of peptic ulcer (better tolerated drugs are used for this indication)
37
Q

Adverse effects / side effects/ contraindications of oxybutynin

A

Parasympatholytic effects: mydriasis (pupillary dilation), tachycardia, decrease GI motility, decrease secretions

Contraindications:

  1. pyloric obstruction; retentive bladder
  2. narrow-angle glaucoma
38
Q

What are non-depolarising NMBAs?

A
  1. Block Nm nicotinic ACh receptors
  2. Block neurotransmission at Nm junctions
  3. Paralysis of skeletal muscles
39
Q

Characteristics of non-depolarising NMBAs

A
  1. Poor oral absorption
  2. Low lipid solubility → do not penetrate BBB
  3. Small Vd
40
Q

Types of non-depolarising NMBAs

A

Short-acting: Rocuronium (0.5-3mins)
Intermediate-acting: Pancurorium, Atracurium (2-5mins)
Long-acting: Tubocurarine (2-13mins)

41
Q

MOA & uses of Pancuronium

A
  1. competitive antagonists of Nm nicotinic acetylcholine receptor
  2. non-depolarising blockade results in skeletal muscle paralysis
  3. IV → rapid onset of action and short half-life
  4. clinical uses: indication of paralysis for surgery
42
Q

Side effects of pancuronium

A
  1. Histamine release at higher doses: flushing, oedema, erythema, hypotension, tachycardia
  2. Weak antimuscarinic activity: increase HR, increase CO due to vagolytic effects
43
Q

Types of indirect anticholinergic drugs

A
  1. depolarising neuromuscular blocking agents (NMBAs): succinylcholine
  2. presynaptic toxin: botulinum toxin
44
Q

MOA and uses of succinylcholine

A
  1. Nm nicotinic acetylcholine receptor agonist
    Phase 1 → opens sodium channels associated with nAChR → depolarisation → fasciculations
    Phase 2 → continuous depolarisation → gradual repolarisation as the sodium channels close or is blocked → resistance to depolarisation → flaccid paralysis (depolarising blockade)
  2. clinical use: paralysis for brief surgical procedures
45
Q

Adverse effects of succinylcholine

A
  1. Malignant hyperthermia
  2. Apnea
  3. Hypotension, arrhythmias, respiratory collapse
46
Q

MOA and uses of botulinum toxin

A
  1. Cleaves SNARE proteins preventing exocytosis of ACh containing synaptic vesicles
  2. clincial uses: cervical dystonia, blepharospasm, strabismus, migraine and other headache disorders, upper limb spasticity
47
Q

Side effects of botulinum toxin

A
  1. paralysis of wrong muscle group

2. allergic reactions

A. General Pharmacology (7 decks)

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