NDM Relaxant eLFH Flashcards
How are non-depolarising muscle relaxants structurally related to ACh?
through a common QUATERNARY AMMONIUM group.
It is the N+ -containing group of ACh that is responsible for the affinity to its binding site on the α subunit.
They act as antagonists by exhibiting affinity with no intrinsic activity.
What are the classifications of NDM relaxants?
- Benzylisoquinolinium compounds
2. Aminosteroid compounds
What percentage of receptors are NMJ must be occupied to produce neuromuscular block?
More than 90%
What agents are in the Benzylisoquinolinium group?
Atracurium, Mivacurium, Tubocurarine.
Two quaternary ammonium groups linked by a chain of methylene groups.
What aspect of structure in Atracurium causes histamine response?
the quaternary ammonium groups.
How is atracurium metabolised?
Hydrolysis by non-specific esterases in the plasma at ester group.
How is mivacurium metabolised?
hydrolysis by plasma cholinesterase at ester group.
What is the structure of aminosteriod group?
Which agents does this include?
composed of one or two quaternary ammonium groups inserted into the steroid nucleus.
Ie. Rocuronium, Vecuronium.
What part of the molecule allows deacetylation in the liver in Pancuronium?
ACETYL - ESTER LINK
at the 3-C position
Which muscle relaxant structure allows it to be excreted unchanged in bile and urine?
rocuronium which has a 3-OH group.
What TOF ratio is seen in non-depolarising blocks?
< 0.7
What TOF is seen in depolarising blocks?
In a depolarising block, the twitch amplitudes are similar from T1 to T4 and the TOF ratio is
> 0.7
What is post tetanic potentiation?
Post-tetanic potentiation or facilitation is the phenomenon where, following a tetanic stimulus of 50 Hz for 5 s, there is a temporary increase in the twitch amplitude.
Exhibited by NDMRs, not Sux.
What medication can prolong duration of block?
Pre-junctionally: Tetracyclines, Aminoglycosides and Magnesium by competing with Calcium mechanism, reducing ACh release.
Post-junctionally: volatile agents, LA, steroids, Ca antagonists, TCA’s
What physiological disturbances/ states can prolong NM block?
Acidaemia
Hypothermia
Advanced age
Hypermagnesaemia
Hypokalaemia
Hypocalcaemia
How does Myasthenia Gravis affect NM blockade?
Myasthenia gravis is associated with a reduced number of post-junctional nicotinic ACh receptors,
and therefore a given mass of drug occupies a greater proportion of receptors,
= RAPID ONSET
= PROLONGED DURATION BLOCK
How does 1Hz stimulus affect:
Depolarising vs non-depolarising block?
Sustained (depolarising) vs fade (non-depol)
TOF ratio in depolarising vs non-depolarising?
Depolarising: > 0.7
NDMR: < 0.7
How is Dantrolene constituted?
Dantrolene is available as capsules and in vials as an orange powder containing 20 mg dantrolene, 3 g mannitol and sodium hydroxide.
Each vial when reconstituted with 60 ml water has a pH of 9.5.
What drugs trigger malignant hyperthermia?
Sux and all volatile agents only.
Hofmann elimination accounts for how much of atracurium elimination?
40%
What processes slow down Hofmann degradation?
Acidosis and hypothermia will slow down the process of Hofmann elimination.
Laudanosine is the breakdown product of which process?
BOTH
ester hydrolysis and Hofmann degradation
Potency of atracurium vs cis-atracurium?
CIS-ATRACURIUM: 3-4 times more potent.
How is cis-atracurium predominantly metabolised?
Hofmann elimination,
Which muscle relaxants can cause critical illness myopathy?
All muscle relaxants with long-term use.
How is Vecuronium presented?
It is unstable in solution and therefore presented as a freeze-dried powder containing mannitol and sodium hydroxide.
