3. Neuromuscular Blockers, Reversal Agents, Muscarinic Antagonists Flashcards
nicotine receptor location
autonomic ganglia
nicotine action
agonist
or
antagonist
nicotine use
smoking cessation
succinylcholine receptor location
NMJ
succinylcholine action
agonist
or
antagonist
rocuronium receptor location
NMJ
rocuronium action
antagonist
pancuronium receptor location
NMJ
pancuronium action
antagonist
vecuronium action
antagonist
botulinum toxin receptor location
NMJ
botulinum action
indirect acting antagonist
*inhibiting SNARE proteins so no NT can be released
botulinum use
cosmetic
blepharospasm
cervical dystonia
focused msucle relaxant
nicotinic receptor antagonists
nicotine
succinylcholine
rocuronium
pancuronium
vecuronium
botulinum toxin
nicotinic receptor type
ion channel
how many Ach molecules binding to NAchR provide max effect?
2 Ach bind to alpha subunits
how is Ach broken down?
acetycholineesterase
direct agonist
acting on the nAchR
agonist/antagonist
stimulate initially
stay bound longer which would be an antagonist to target NT
fetal receptors
enhanced response to D agent
relative resistance to ND agent
margin of safety
- 10% need to be activated to initial muscle Action Potential
- more NT than needed for each AP
- significant reserve capacity
Clinical evidence of block
75% of nicotinic receptors occupied by antagonist before clinical evidence of block
Complete suppression
95% nicotinic receptors occupied by antagonist
NMBs structure
NCH4+ functional group
functional duplicates of ACh
cations
Cations absorption
poor PO
avoid CNS penetration
- poor BBB passage
Depolarizing MR MOA
acts as agonist
then antagonist to Ach
binds Ach receptor
persistent depolarization of endplate
blocks Ach until it diffuses away
Depolarizing MR metabolism
slower than Ach
Non-Depolarizing MR MOA
competitive antagonist
Depolarizing MR Phase 1 block
depolarizing phase
persistant –> paralysis
Depolarizing MR phase 2 block
only happens w/lgr than recc doses or infusions
desensitizing phase
blocks conversion from depolarization to non-depolarizing block
MR blocks Ach
Depolarizing MR metabolism
slower than Ach
- not degraded by AchE
Non-depolarizing MR
competitive with Ach to bind w/nicotinic recepotr of end plate
bloc inhibits Ach from binding
how to reverse NDMR
AChE inhibitor
- neostigmine
surmountable
block can eventually be overcome
succinuylcholine onset/duration
rapid onset
- low lipid solubilty
- cation effect
- water soluble
short duration of action
- diffuses away quickly
Prolong Succinycholine duration
increase dose
continuous ijnfusion
decrease rate of metabolism
Succinylcholine metabolism
quick metabolism by pseudocholinesterase (plasma)
Succinylcholine DOA factors
hypothermia
- decrease hydrolysis
low enzyme (psuedocholinesterase)
- pregnancy, liver disease, renal fail
- drug interactions
- prolong 2-20 min
genetic
- heterozygotes (20-30min duration)
- homozygotes (4-8 hrs)
drugs that decrease psuedocholinesterase activity
neostimine
metoclopramide
esmolol
oral contraceptives
dibucaine
echothiophate
phenelzine
pancuronium
dibucaine number
measures enzyme function
dibucaine normal enzyme
80%
dibucaine homozygote number
20%
Succinylcholine drug interactions
cholinesterase inhibitors
- prolong phase 1 block
- reduce metabolism of sux
- pts w/myasthenia gravis/glaucoma
Nondepolarizing agents
- small dose may be antagonistic
- in phase 2 block, NDMR enhances
block
Succinylcholine dose
2 x ED95
ED95 = 0.35-0.5 mg/kg
Succinylcholine dose neonate
larger weight-based dose
(lgr mg/kg)
- higher Vd
Succ continuous infusion
2 mg/mL or 1 mg/mL
need nerve stimulation
Succ CV effects
- may act at ganglia and muscarinic receptors
- depends on underlying state
- leads to bradycardia w/elevated vagal tone
- peds more susceptible
- fasciculation
- hyperkalemia (incr serum0.5 mEq/L)
Manage Succ bradycardia
Atropine/Glycopyrrolate
denervation injury due to receptor upregulation
immature isoform
more spread out receptors
widespread depolarization
extensive K release
risk peaks 7-10 days post trauma
burn, trauma, neurological conds