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Pharmacology > Muscle Relaxants, NMBA (L&J Chp 14) > Flashcards

Muscle Relaxants, NMBA (L&J Chp 14) Flashcards

1
Q

Succinylcholine dose - dogs

A

0.3-0.4mgkg

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2
Q

Succinylcholine dose - cats

A

0.2mgkg

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3
Q

Succinylcholine dose - horses

A

0.12-0.15mgkg

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4
Q

Pancuronium dose - dogs

A

0.07-0.1mgkg

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5
Q

Pancuronium dose - cats

A

0.06-0.1mgkg

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6
Q

Pancuronium dose - horse

A

0.12mgkg

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7
Q

Atracurium dose - dogs

A

0.1-0.2mgkg

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8
Q

Atracurium dose - cats

A

0.1-0.25mgkg

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9
Q

Atracurium dose - horses

A

0.07-0.15mgkg

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10
Q

Vecuronium dose - dogs

A

0.1mgkg

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11
Q

Vecuronium dose - cats

A

0.025-0.1mgkg

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12
Q

Vecuronium dose - horses

A

0.1mgkg

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13
Q

Pipecuronium dose - cats

A

0.003mgkg

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14
Q

Pipecuronium dose - dogs

A

0.05mgkg

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15
Q

Cisatracurium dose - dogs

A

0.075-0.3mgkg

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16
Q

Cisatracurium dose - cats

A

0.05-0.3mgkg

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17
Q

Mivacurium dose - dogs

A

0.01-0.05mgkg

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18
Q

Mivacurium dose - cats

A

0.08mgkg

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19
Q

Rocuronium dose - dogs

A

0.1-0.6mgkg

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20
Q

Rocuronium dose - cats

A

0.1-0.6mgkg

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21
Q

Doxacurium dose - dogs

A

0.002-0.005mgkg

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22
Q

Gantacurium (GW280430A) dose - dogs

A

0.06mgkg

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23
Q

Gentacurium (GW280430A) dose - cats

A

0.06mgkg

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24
Q

Rocuronium dose - horses

A

0.3-0.6mgkg

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25
Q

Pancuronium

A
  • Non-depol (competitive) NMBA
  • Steroid molecule-based structure
  • Dose-dependent onset ~5’
  • Repeated doses = cumulative effect –> infusion not common
  • Duration of action 40-60’
  • Mostly renal excretion with some hepatic metabolism –> prolonged duration of action in patients with renal insufficiency
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26
Q

Pancuronium and CV effects

A
  • Blocks cardiac muscarinic R, increasing HR
  • Effect varies among species - usually not a clinical concern
  • Muscarinic blocking effect, associated tachycardia appear to be due to second positive charge on steroid ring
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27
Q

Difference btw pancuronium and vecuronium

A

Pancuronium - single methyl group (and thus positive charge) = vecuronium –> no CV effects

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28
Q

Atracurium

A
  • Short-acting, non-depolarizing (competitive) NBMA
  • Benzolisoquinoline structure similar to that of d-tubocurarine
  • Dose-dependent onset approx 5’
  • Dose-dependent duration in dogs approx 30’
  • Repeated doses do not tend to be cumulative so longer term maintenance of NMB via infusion is viable
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29
Q

Atracurium elimination

A
  • Almost half of drug degraded by Hoffmann elimination, nonspecific ester hydrolysis
  • Remaining fraction of the drug degraded by undefined routes –> no evidence of prolonged action in humans with renal or hepatic insufficiency
  • Can be safely given to patients with hepatic or renal insufficiency without an increase in duration of action
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30
Q

Atracurium: Hoffman elimination…

A

Does not require enzymatic activity

Is not a biologic proces

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31
Q

Storage of atracurium

A

Drug should be refrigerated

Supplied at pH 3.25-3.65 to slow degradation

32
Q

What happens when atracurium injected IV…

A
  • When injected at physiologic pH/temperature, spontaneously decomposes into laudanosine and quaternary monoacrylate
33
Q

Laudanosine

A
  • Byproduct of atracurium, cis-atracurium metabolism
  • has potential to induce seizures
  • Dependent on hepatic clearance –> plasma concentrations may be elevated in patients with hepatic insufficiency
34
Q

Are the theoretical concerns of laudanosine clinical concerns as well?

A

-Laudanosine-induced CNS stimulation/resultant seizures unlikely in clinical patients unless drug used for prolonged periods of time as might occur in intensive care settings

35
Q

What will increase duration of NMB using atracurium/decrease CRI rate?

A
  • Hypothermia
  • Hofmann elimination is pH/temperature dependent so hypothermia will increase duration of NMB and decrease infusion rate necessary to maintain NMB
36
Q

Esterhydrolysis of atracurium

A
  • Accomplished by several plasma esterases not related to plasma cholinesterase
  • Duration of action not prolonged in the presence of cholinesterase inhibitors (in contrast to depolarizing NMBA succinylcholine)
37
Q

NMBA with benzylisoquinolone structure

A

-Associated with histamine release –> varying degree of resultant hypotension

38
Q

d-Tubocurarine

A
  • Prototypical benzylisoquinolone NMBA

- Most potent histamine-releasing NMBA

39
Q

What is true about the newer NMBA (atracurium, cisatracurium) having the benzylisoquinolone structure?

A
  • Require several times the ED95 dose required for NMB before appreciable amounts of histamine are released
  • Hypotension, tachycardia not usually observed in clinical cases
40
Q

Atracurium Composition

A

-racemic mixture of ten optical isomers

41
Q

Cisatracurium

A
  • 1R-cis, 1R’-cis isomer

- Comprises approximately 15% of racemic atracurium –> approx 4x potency, reduced potential for histamine release

42
Q

Cisatracurium onset, duration of action

A

-Similar to atracurium

43
Q

Elimination of cisatracurium

A
  • Hofmann elimination responsible for greater than half administered dose of cisatracurium
  • No ester hydrolysis
44
Q

Production of laudanosine with cisatracurium metabolism

A
  • Hofmann elimination –> laudanosine production

- Since 4x as potent as atracurium, can give lower dose so have less laudanosine production

45
Q

Where do NMBA exert their effects?

A
  • NMJ

- Motor end plate

46
Q

NMJ

A

-Forms interface btw large myelinated motor nerve and muscle supplied by the nerve

47
Q

Parts of NMJ

A
  • Prejunctional motor nerve ending
  • Synaptic cleft
  • Postjunctional membrane of the skeletal muscle fiber
48
Q

What type of receptor is present on the pre junctional area of the NMJ?

A

Nicotinic R

49
Q

What type of receptor is present on the postjunctional area of the NMJ?

A

Nicotinic R

50
Q

Nicotinic R

A
  • Receptor type on the pre/post junctional area of the NMJ

- Bind/respond to ACh or another suitable ligand

51
Q

Prejunctional receptor

A

Thought to be important in the synthesis and mobilization of ACh stores but not in its release

52
Q

Two types of post junctional receptors

A
  • Junctional

- Extrajunctional

53
Q

Junctional post junctional receptors

A
  • Found on the motor endplates of normal adult animals
  • Responsible for binding with released ACh –> effecting muscle ctx –> therefore responsible for relaxant effect when NMBA administered
54
Q

Extrajunctional post junctional receptors

A
  • Not normally present in muscles of typical adults

- Present in neonates

55
Q

Why are extrajunctional post junctional receptors important?

A
  • Synthesized by muscles receiving less than normal degree of motor nerve stimulation
  • Produced by muscles following spinal cord or peripheral nerve injury or after period of disuse as when limb is casted
56
Q

Where are extrajunctional post junctional receptors located?

A

Not restricted to the motor endplate

May be located over the entire muscle surface

57
Q

What is true about extrajunctional post junctional receptors and NMBA?

A
  • Appear to be more sensitive to depolarizing NMBA, less sensitive to non depolarizing NMBA
  • If the degree of neural deficit is severe, extrajunctional receptors may be numerous and widely distributed over the muscle membrane
  • Such patients may very different responses to actions of depolarizing NMBA and thus profound release of intracellular K+ with concomitant adverse cardiac effects may result if succinylcholine is administered to these patients
58
Q

-Binding of ligands to the receptor is what kind of process?

A

Competitive
Whichever suitable ligand is present in highest concentrations in the vicinity of the receptor will win the competition and affect the outcome

59
Q

What advantage does an antagonist have over an agonist related to binding on the alpha subunits?

A
  • Two molecules of ACh required to bind to each of the alpha subunits on the R
  • Antagonists: need only to bind to one of the subunits to present normal NM transmission
  • Ctx of the muscle does not occur in response to motor nerve depolarization and paralysis results
60
Q

Interaction of ACh and NMBA at the post junctional receptors

A

Dynamic process of binding and release
Depends on the sheer number of receptors present (10-20,000/micrometer^2)
So: success or failure of NM transmission in the presence of NMBA is determined by the concentration of NMBA vs concentration of ACh

61
Q

What determines the success/failure of NM transmission in presence of NMBA?

A

success or failure of NM transmission in the presence of NMBA is determined by the concentration of NMBA vs concentration of ACh

62
Q

High % of R binding ACh…

A

Favoring of muscle contraction

63
Q

High % of R binding NMBA…

A

Favoring paralysis

64
Q

Mechanism of reversing paralysis induced by NMBA

A
  • Increasing concentration of ACh compared with concentration of NMBA will increase probability that ACh will win competition for R and restore normal NM transmission
  • Clinically: accomplished by administration of AChE inhibitors
65
Q

What happens when anticholinesterase drug administered?

A
  • eg neostigmine
  • Available ACh not degraded immediately but persists within the synapse
  • Able to repeatedly interact with receptors –> tips competitive balance in favor of ACh –> more R participate in current flow, global muscle strength increases
  • Interaction also seen as the activity of a NMBA wanes due to drug elimination
66
Q

Rocuronium

A
  • Derivative of vecuronium

- Approximately 1/8th potency

67
Q

Rocuronium vs vecuronium

A

-Similar molecular weights but rocuronium has a lower potency so larger injected dose of rocuronium places greater number of molecules near NMJ –> more rapid onset of blockade

68
Q

Rocuronium clinical uses

A
  • Similar duration of atracurium, vecuronium
  • More rapid onset but cannot provide optimal conditions for human intubation as quickly as succinylcholine
  • Virtually no CV effects
  • No histamine release
69
Q

Rocuronium elimination

A

Primary route - hepatic clearance

Small fraction eliminated by the kidney

70
Q

Rocuronium reversal

A

Administration of suggammadex

71
Q

Suggammadex

A

Used for reversal of rocuronium, vecuronium

Chelating agent that preferentially binds to, physically removes the NMBA from the motor end plate

72
Q

Pipercuronium

A

Steroid relaxant derived from pancuronium

73
Q

Differences btw pipercuronium and pancuronium

A
  • Manipulation of the steroid structure –> greatly reduced antimuscarinic effects
  • Piper = free of tachycardic effects while retaining long duration of action
  • Can cause hypotension in dogs
74
Q

Pipercuronium elimination

A

-Eliminated primarily by renal route with smaller fraction undergoing biliary excretion

75
Q

Vecuronium

A

-First NMBA devoid of CV effects

Pharmacology (7 decks)

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