Non-depolarizing muscle relaxants: general properties

Question 1

With regard to non-depolarising muscle relaxants, they (true or false):

Always contain a N+ group

Answer 1

True. It is the N+ group which is responsible for affinity to the binding site; bisquaternary compounds have greater affinity than monoquaternary ones.

Question 2

With regard to non-depolarising muscle relaxants, they (true or false):

Are highly ionized, lipid soluble compounds

Answer 2

False. They are highly ionized but are poorly lipid soluble.

Question 3

With regard to non-depolarising muscle relaxants, they (true or false):

Bind to the α subunit of the muscarinic ACh receptor

Answer 3

False. They bind to the α subunit of the nicotinic ACh receptor.

Question 4

With regard to non-depolarising muscle relaxants, they (true or false):

Form an ionic bond with the ACh receptor

Answer 4

True

Question 5

With regard to non-depolarising muscle relaxants, they (true or false):

Are metabolised at the neuromuscular junction

Answer 5

False. No, their action is terminated by diffusion away from the NMJ. The site of metabolism depends on the chemical structure.

Question 6

Hypercalcaemia is associated with prolonged neuromuscular block (true of false).

Answer 6

False. It is hypocalcaemia and Ca2+-channel antagonists which prolong neuromuscular block. Remember the crucial role of Ca2 in vesicle discharge.

Hypermagnesaemia and hypokalaemia are also associated with prolonged block.

Question 7

Acidaemia is associated with prolonged neuromuscular block (true of false).

Answer 7

True. Acidaemia favours the protonation of monoquaternary ammonium compounds, converting them to bisquaternary molecules and increasing their affinity for the nicotinic ACh receptor. In addition, acidaemia disrupts the optimal working environment of enzymes.

Question 8

Myasthenia gravis is associated with prolonged neuromuscular block (true of false).

Answer 8

True. Myasthenia gravis results in a reduced number of post-junctional ACh receptors and thus increases the depth and duration of block induced by non-depolarising muscle relaxants.

Question 9

Ciprofloxacin is associated with prolonged neuromuscular block (true of false).

Answer 9

False. The quinolone antibiotics are not known to interfere with neuromuscular function, unlike the aminoglycosides and tetracycline.

Question 10

Trazadone is associated with prolonged neuromuscular block (true of false).

Answer 10

True. Trazadone is a tricyclic antidepressant and thus prolongs neuromuscular block.