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Pharmacology I > 17. Central and peripheral myorelaxant drugs > Flashcards

17. Central and peripheral myorelaxant drugs Flashcards

1
Q

Use of myorelaxant drugs

A
  • During surgical anaesthesia to obtain skeletal muscle relaxation
  • Assist in intubation
  • Corneal/retinal surgery
  • Therapy of spastic disorders
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2
Q

Competitive neuromuscular blocking agents: Function

A

Selectively antagonise nicotinic receptors by preventing endogenous ACh binding & subsequent muscle cell depolarisation

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3
Q

Give the classes of neuromuscular blocking agent

A
  • Competitive (non-depolarising)
  • Depolarising
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4
Q

Competetive neuromuscular blocking agents:

To produce a complete block…% of receptors must be blocked

A

90%

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5
Q

Competitive neuromuscular blocking agents: properties

A
  • Ionised and water-soluble
  • Onset is slow & short duration
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6
Q

Competitive neuromuscular blocking agents: Metabolism & excretion

A
  • Metabolised in liver
  • Excreted by kidenys
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7
Q

Competitive neuromuscular blocking agents are antagonised by…

A

Cholinesterase inhibitors (Neostigmine)

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8
Q

Competitive neuromuscular blocking agents: Effect

A
  1. Motor weakness →
  2. Flaccid paralysis of skeletal muscles
  • ↓ Blood pressure
  • ↓ Coagulability of blood because of heparin release from mast cells
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9
Q

Competitive neuromuscular blocking agents: Examples

A
  • Curare (Histamine release)
  • Gallamine (Tachycardia; long-acting)
  • Atracurium (Safe in liver & kidney disease; most used; intermediate action)
  • Cisatracurium (intermediate-acting)
  • Rocuronium (intermediate-acting)
  • Vecuronium (intermediate-acting)
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10
Q

Central muscle relaxants

A

Relative specific depressant action in CNS

  • Causing ↓ motor activity/paralysis of voluntary muscles without LOC
  • Do not inhibit other CNS functions
  • Can potentiate the effect of anaesthetics and combinations
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11
Q

Central muscle relaxants: Examples

A
  • Guaiphenesin
  • Baclophen
  • Carisoprodol
  • Methocarbamol
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12
Q

Guaiphenesin

A
  • Spinal interneuronal blocking agent
  • Used to adjunct anaesthesia
  • Blocks polysynaptic and not monosynaptic reflexes
  • Effective against:
    • Convulsions
    • Tetanus
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13
Q

Baclophen

A
  • GABAB receptor agonist in CNS
  • Causes hyperpolarisation of neurons due to ↑ K+ ion conductance
  • Large therapeutic index
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14
Q

Carisoprodol

A

Useful for pain - Due to analgesic-sparing effect on opioid analgesics

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15
Q

Methocarbamol

A
  • Acts on internuncial neurones of the spinal cord
  • ↓ Skeletal muscle hyperactivity
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16
Q

Depolarising neuromuscular blocking agents: Function

A
  1. Stimulates opening of nicotinic ACh receptor channel
  2. Produces depolarisation of cell membrane
  3. Succinylcholine persists at neuroeffector junction, activating nicotinic receptor channels continuously
  4. Inactivation of voltage-gated Na+ channels → Cannot support further APs
17
Q

Depolarising neuromuscular blocking agents: Properties

A

Rapid onset; short duration

18
Q

Neuromuscular blocking drugs do not produce…

A

Analgesia

19
Q

Metabolism of depolarising neuromuscular blocking agents

A

Metabolised by plasma pseudocholinesterase & liver

20
Q

Depolarising neuromuscular blocking agents: Example

A

Succinylcholine

21
Q

Succinylcholine

A
  • Dog, cattle, sheep are sensitive
  • Weakness & paralysis of skeletal muscles
  • ↑ Blood pressure
22
Q

Succinylcholine: Side effects

A
  • Bradycardia
  • Hyperkalaemia
  • ↑ intraoccular & intragastric pressure
  • Anaphylaxis
23
Q

Succinylcholine: Phase I block

A
  • Depolarising block of motor end-plate
24
Q

Succinylcholine: Phase II block

A
  • Competetive block of motor end-plate/partially susceptible to reversal by cholinesterase inhibitors
25
Q

“Muscle relaxants” refers to which 2 therapeutic groups?

A
  • Neuromuscular blockers
  • Spasmolytics
26
Q

Spasmolytics: Use

A

Alleviate musculoskeletal pain and spasms

  • Specifically depress the CNS → ↓ Motor activity/ paralysis
  • No LOC
  • May cause drowsiness/sedation
27
Q

Neuromuscular blocking drugs: Aims

A
  • Relax skeletal muscles for surgery
  • Reduction of dislocations and fractures
28
Q

Neuromuscular blocking drugs: Function

A

Interferes with transmission at NMJ → Relaxation/paralysis

29
Q

Spasmolytics-smooth muscle relaxants

A

Parasympatholytics, Sympathomimetics, direct acting substances

30
Q

Spasmolytics-smooth muscle relaxants: Examples

A
  • Papaverine
  • Drotaverine
31
Q

Papaverine: Effect

A
  • Reduces spasm of visceral smooth muscle
  • Vasodilation
  • Bronchodilation
  • ↓ Heart excitability
32
Q

Papaverine: Indications

A
  • Excessive smooth muscle contraction
  • Urethral spasm
  • Colic spasm
  • Bronchial spasm
  • Relax uterus (drotaverine)

Pharmacology I (19 decks)

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