Anticholinesterases and Anticholinergics, NMB Reversal Flashcards
Acetycholinesterase AChE
enzyme that hydrolyzes acetylcholine
inhibition of AChE allows for more ___ which facilitates?
ACh
- depolarization and muscle contraction
Mechanisms of Action for Anticholinesterases
inhibit AChE – by being hydrolyzed by the AChE, causing carbamylation of AChE or by attaching to the enzyme
Mechanisms of Action for Anticholinesterases
Presynaptic effects – cause increased availability of ACh, cause spontaneous contractions in the absence of NMB
Mechanisms of Action of Anticholinesterases
Direct effect on NMJ – too much ACh at the NMJ causes decreased sensitivity resulting in blockade effect
Neostigmine and pyridiostigmine _____ with Ach to be hydrolyzed by the AChE, then cause the enzyme to be _______and decrease its ability to hydrolyze Ach
compete
-carbamylated
Edrophonium is not broken down by the _____, but attaches to it electrostatically to decrease its ability to _____ ACh
-AChE
- hydrolyze
Carbamylated AChE is a ____ inhibition
reversible- 1/2 life of 15-30 min
which drugs are hydrolyzed by AChE, cause chemical change in the enzyme and reversibly inhibit its ability to hydrolyze ACh.
Neostigmine, Pyridostigmine and Physostigmine
What type of attachment is performed by edrophonium and is reversible
electrostatic bound/attachment
Edrophonium forms a reversible ______ attachment to AChE to inhibit its ability to hydrolyze ACh (it competes with ACh for the bonding site with AChE).
-electrostatic
-Edrophonium is not broken down by AChE, but attaches to it electrostatically to decrease its ability to hydrolyze ACh
____ forms an irreversible complex that must be replaced with generation of new enzyme.
Organophosphate anticholinesterase
examples of organophosphate anticholinesterases
Echothiophate – eye gtts
Insecticides
Nerve gases – tabum, saran, soman
Quaternary ammonium are ionized, _____ soluble and ____ insoluble
-water
- lipid
examples of drugs that are quaternary ammonium
Neostigmine, pyridostigmine, edrophonium
-Poor lipid solubility (cant cross blood brain barrier), water soluble
Tertiary amine properties:
-not ionized
- lipid soluble
which drug is a tertiary amine
physostigmine
Neostigmine (Prostigmine) dose , onset and elimination
0.06
-7-11 min
- 50% renal, 50% plasma esterases and hepatic metabolism
Edrophonium (Enlon) dose, onset, and elimination
Dose 0.5-1 mg/kg
Onset 30-60 seconds (presynaptic effect)
Elimination 75% renal
Pyridostigmine (Mestinon) onset, dose, and elimination
Dose 0.3 mg/kg
Onset 10 – 20 minutes
Elimination 75% renal
Physostigmine (Antilirium) dose, onset, elimination
Dose 0.5 – 2 mg (0.01-0.03 mg/kg) – give slowly(projectile vomiting) (1 mg/min)
Onset about 5 minutes
Elimination hepatic and hydrolysis by cholinesterases
Used to treat CNS effects of anticholinergic agents, anesthetics, and reduces shivering
Deep NMB reversed better with what drug?
Neostigmine
Endrophonium works better with
atracurium
Neostigmine works better with
Vecuronium
Ceiling effect:
Once AChE is maximally inhibited, giving more anticholinesterase will not reverse a NM block.
Max dose Neostigmine 0.07 mg/kg
Reversal of NMB affected by:
ANtibiotics, hypothermia, respiratory acidosis(PaCO2 > 50 mmHG) and hypokalemia- metabolic acidosis
Nicotinic receptors (cholinergic) all located within
ANS ganglion and at NMJ
Muscarinic receptors M1=
CNS, stomach
M2
principally in the heart, also airway smooth muscles
M3=
airway smooth muscles and salivary glands, contraction and secretion
Effects of Anticholinesterases: Cardiovascular
Cardiovascular
Bradycardia, junctional rhythm, PVCs, ventricular rhythm, asystole
Slowing of conduction – AV node
GI/GU effects
Increased secretions
Increased motility (treatment for paralytic ileus)
PONV- postoperative n/v
Pulmonary effects
Bronchoconstriction
Increased secretions
Opthalmic
Miosis – pupil constriction
Constriction of ciliary muscle (far-sighted)
Decreased intraocular pressure