Neuromuscular Blocking Drugs & Reversal Agents Flashcards
(121 cards)
Name the first successful administration of curare to produce relaxation in 1912
Arthur Lawen
How does Succs work?
Succ produces a prolonged depolarization of the endplate region that results in desensitization of nicotinic acetylcholine receptors; inactivation of voltage gated sodium channels at the neuromuscular junction and increase in potassium permeability in the surrounding membrane. Thus producing the failure of the action potential generation due to membrane hyperpolarization and a block ensues
where is Acetylcholinesterase found?
what is it responsible for?
what are the two end products?
(“true” cholinesterase) is present at the neuromuscular junction
responsible for the rapid hydrolysis of released acetylcholine to
ACETIC ACID & CHOLINE
Butyrylcholinesterase
where is it synthesized?
what does it do and where?
(plasma cholinesterase or pseudocholinesterase) is synthesized in the liver.
It catalyzes (causes or accelerates) the hydrolysis of succinylcholine
which occurs mainly in the plasma.
Structure of neuromuscular blockers
2 points
what is the exception?
All neuromuscular blockers are quaternary ammonium compounds and are structurally related to acetylcholine.
Majority of NMBD are synthetic alkaloids
Exception is tubocurarine which is extracted from and Amazonian vine. It is cheaper to isolate from this plant than to synthesized.
Steroidal: presence of acetyl ester (Ach like) is thought to facilitate what?
thought to facilitate interactions of steroidal compounds with nicotinic acetylcholine receptors at the at the postsynaptic muscle membrane.
Tubocurarine:
who is it not suitable for
Monoquarternary, long acting
No active metabolism
Excreted unchanged in urine; liver is secondary
Not suitable for renal or liver failure patients
Onset slow
Duration is long
Recovery slow
Tubocurarine: intubating and maintenance
Intubating dose 0.5 – 0.6 mg/kg
Maintenance dose are 0.1 – 0.2 mg/kg
Atracurium
Racemic mixture of 10 stereoisomers
Isomers are separated into 3 geometrical isomer groups that are designated cis-cis, cis-trans, and trans-trans
Designed to undergo spontaneous degradation at physiologic temp and pH by Hofmann elimination yielding a laudanosine (tertiary amine) and a monoquaternary acrylate metabolite
Can undergo ester hydrolysis
Hoffmann elimination fragments atricurium to laudanosine and a monoquaternary acrylate
Laudanosine depends on the liver for clearance with ~70% excreted in bile with remainder in the urine
Atracurium (continued)
laudanosine does what?
Hepatic cirrhosis in humans does not alter clearance of laudanosine (metabolite)
Excretion of this metabolite is impaired in patients with biliary obstruction
Laudanosine easily crosses the BBB and has CNS stimulating properties
No evidence that shows normal or impaired renal function is likely to result in concentrations of laudanosine capable to produce convulsions.
Elimination of laudanosine is similar with normal or impaired renal function
Cisatracurium
Hoffman accounts for how much
how potent?
laudanosine?
Isomer of atracurium
Hoffman elimination to laudanosine and a monoquaternary alcohol metabolie
No ester hydrolysis of parent molecule
Hoffman is ~ 77% of clearance
23% is cleared by other organs with 16% being renal
4-5 times as potent as atricurium
5 times less laudanosine is produced and is thought to be of no clinical consequence
Does not cause histamine release like atracurium if given in clinical dose range
Mivacurium
Only currently available short acting NMBD
Discontinued in US (not because of safety reasons)
Mixture of 3 stereoisomers
Metabolized by butylcholinesterase at about 70-88% the rate of Sch to a monoester
May produce histamine release especially if given rapidly
Pancuronium
duration?
inhibiting properties?
shelf life?
name the metabolite that increases duration
Potent long acting
Vagolytic and butyrylcholinesterase inhibiting properties
~40-60% eliminated by kidneys and 11% in bile
15-20% metabolized by deacetylation in liver
3-OH, 17-OH, and 3,7-di-OH are less potent metabolites and excreted in urine
Accumulation of 3-OH metabolite is responsible for prolongation of the duration of Pancuronium
At room temperature remains stable for 6 months- good for military overseas stuff
Vecuronium
tell me about vagolytic properties
elimination?
what metabolite creates prolonged administration?
Monoquarternary with intermediate duration of action
Has a minor molecular difference from pancuronium characterized by:
Slight decrease in potency
Loss of vagolytic properties
Molecular instability in solution explaining shorter duration
Increased in lipid solubility resulting in greater biliary elimination of Vecuronium than pancuronium
Principle elimination is liver with renal accounting for about 30%
30-40% cleared in bile
Duration relies on liver function more so than renal function
Metabolized to 3-OH, 17-OH, 3,17-di-OH
3-OH has 80% the neuromuscular blocking potency of Vecuronium and with prolonged administration this metabolite may contribute to prolonged neuromuscular blockade
Rocuronium
Intermediately acting monoquaternary neuromuscular blocker with fast onset
6 times less potent than Vecuronium
Primarily eliminated by liver and excreted in bile
Carried to liver by carrier-mediated active transport system
30% excreted unchanged in urine
Remains stable for 60 days at room temperature
what effects your roc?
DES affects your ROC!!!!!
Someone always misses that questions
DES > SEVO > ISO > Halothane > Nitrous Oxide, barbiturate, or propofol
Expressed in terms of dose response relationship
50% depression of twitch height ED50 and 95% would be ED95
Mechanisms for potentiation:
potency of nmbd
Mechanisms for potentiation:
Central effect on alpha motoneurons and interneruonal synapses
Inhibition of postsynaptic nicotinic acetylcholine receptors
Augmentation of antagonist’s affinity at the receptor site
Antibiotics can potentiate neuromuscular blockade:
Aminoglycoside
Polymyxins
Lincomycine
Clindamycin
All inhibit the prejunctional release of acetylcholine and also depress postjunctional nicotinic acetylcholine receptor sensitivity to acetylcholine
Tetracycline exhibit post junctional activity only
what does Hypothermia or Magnesium Sulfate do to the blockers?
Hypothermia or Magnesium Sulfate potentiates blockade of NMBD
High magnesium concentrations inhibit calcium channels at the presynaptic nerve terminals that trigger the release of acetylcholine
Local Anesthetics do what for NMBD
LA given in large doses potentiate but in smaller doses not clinically significant
what does Antidysrhythmics such as quinidine do to NMDB
also potentiate NMBD
Factors decreasing potency of NMBD
Chronic use of anticonvulsant therapy:
thus need for increase doses to achieve block: can be attributed to increased clearance, increased binding of the neuromuscular blockers to alpha 1 acid glycoproteins and/or upregulation of neuromuscular acetylcholine receptors (and street therapy)
factors that decrease potency of NMDB in hyperparathyroidism hypercalcemia and NMBD
In hyperparathyroidism, hypercalcemia is associated with decreased sensitivity to atracurium and thus a short duration of neuromuscular blockade.
Muscle-nerve models have shown hypercalcemia to decrease sensitivity to tubocurarine and pancuronium
When is the ion channel of the Ach receptor closed?
during the resting state