NDM Relaxant eLFH

Question 1

How are non-depolarising muscle relaxants structurally related to ACh?

Answer 1

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.

Question 2

What are the classifications of NDM relaxants?

Answer 2

1. Benzylisoquinolinium compounds

2. Aminosteroid compounds

Question 3

What percentage of receptors are NMJ must be occupied to produce neuromuscular block?

Answer 3

More than 90%

Question 4

What agents are in the Benzylisoquinolinium group?

Answer 4

Atracurium, Mivacurium, Tubocurarine.

Two quaternary ammonium groups linked by a chain of methylene groups.

Question 5

What aspect of structure in Atracurium causes histamine response?

Answer 5

the quaternary ammonium groups.

Question 6

How is atracurium metabolised?

Answer 6

Hydrolysis by non-specific esterases in the plasma at ester group.

Question 7

How is mivacurium metabolised?

Answer 7

hydrolysis by plasma cholinesterase at ester group.

Question 8

What is the structure of aminosteriod group?

Which agents does this include?

Answer 8

composed of one or two quaternary ammonium groups inserted into the steroid nucleus.

Ie. Rocuronium, Vecuronium.

Question 9

What part of the molecule allows deacetylation in the liver in Pancuronium?

Answer 9

ACETYL - ESTER LINK

at the 3-C position

Question 10

Which muscle relaxant structure allows it to be excreted unchanged in bile and urine?

Answer 10

rocuronium which has a 3-OH group.

Question 11

What TOF ratio is seen in non-depolarising blocks?

Answer 11

< 0.7

Question 12

What TOF is seen in depolarising blocks?

Answer 12

In a depolarising block, the twitch amplitudes are similar from T1 to T4 and the TOF ratio is

> 0.7

Question 13

What is post tetanic potentiation?

Answer 13

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.

Question 14

What medication can prolong duration of block?

Answer 14

Pre-junctionally: Tetracyclines, Aminoglycosides and Magnesium by competing with Calcium mechanism, reducing ACh release.

Post-junctionally: volatile agents, LA, steroids, Ca antagonists, TCA’s

Question 15

What physiological disturbances/ states can prolong NM block?

Answer 15

Acidaemia
Hypothermia
Advanced age

Hypermagnesaemia
Hypokalaemia
Hypocalcaemia

Question 16

How does Myasthenia Gravis affect NM blockade?

Answer 16

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

Question 17

How does 1Hz stimulus affect:

Depolarising vs non-depolarising block?

Answer 17

Sustained (depolarising) vs fade (non-depol)

Question 18

TOF ratio in depolarising vs non-depolarising?

Answer 18

Depolarising: > 0.7

NDMR: < 0.7

Question 19

How is Dantrolene constituted?

Answer 19

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.

Question 20

What drugs trigger malignant hyperthermia?

Answer 20

Sux and all volatile agents only.

Question 21

Hofmann elimination accounts for how much of atracurium elimination?

Answer 21

40%

Question 22

What processes slow down Hofmann degradation?

Answer 22

Acidosis and hypothermia will slow down the process of Hofmann elimination.

Question 23

Laudanosine is the breakdown product of which process?

Answer 23

BOTH

ester hydrolysis and Hofmann degradation

Question 24

Potency of atracurium vs cis-atracurium?

Answer 24

CIS-ATRACURIUM: 3-4 times more potent.

Question 25

How is cis-atracurium predominantly metabolised?

Answer 25

Hofmann elimination,

Question 26

Which muscle relaxants can cause critical illness myopathy?

Answer 26

All muscle relaxants with long-term use.

Question 27

How is Vecuronium presented?

Answer 27

It is unstable in solution and therefore presented as a freeze-dried powder containing mannitol and sodium hydroxide.