PHARMACOLOGY - Neuromuscular Blocking Drugs

Question 1

What is the mechanism of action for neuromuscular blocking drugs?

Answer 1

Neuromuscular blocking drugs are competitive antagonists for nicotinic acetylcholine receptors at the neuromuscular junction

Question 2

What is the general structure of neuromuscular blocking drugs?

Answer 2

Rigid, bulky molecules with a central quaternary nitrogen

Question 3

What is the desired affect of neuromuscular blocking drugs?

Answer 3

Flaccid motor paralysis

Question 4

Why are neuromuscular blocking drugs only given after the patient is under general anaesthesia?

Answer 4

Neuromuscular blocking drugs cause complete flaccid motor paralysis without affecting consciousness and they have no analgesic or anaesthetic affects, so it is unethical to give neuromuscular blocking drugs when a patient is not under anaesthesia

Question 5

What are the two last muscles to be affected by neuromuscular blocking drugs?

Answer 5

Intercostal muscles
Diaphragm

Question 6

What are the two main adverse affects of neuromuscular blocking drugs?

Answer 6

Hypotension
Tachycardia

Question 7

How do neuromuscular blocking drugs cause hypotension?

Answer 7

Neuromuscular blocking drugs inadvertently block nicotinic receptors within the ganglia, reducing sympathetic tone resulting in hypotension. Neuromuscular blocking drugs may also stimulate histamine release which can cause hypotension as histamine is a vasodilator

Question 8

How do neuromuscular blocking drugs cause tachycardia?

Answer 8

Neuromuscular blocking drugs cause hypotension which stimulates tachycardia to maintain adequate blood flow and tissue perfusion. Neuromuscular blocking drugs can also inadvertently block muscarinic receptors on the heart which reduces parasympathetic tone resulting in tachycardia

Question 9

Why are neuromuscular blocking drugs incapable of crossing cell membranes?

Answer 9

The central quaternary nitrogen makes neuromuscular blocking drugs inherently charged and thus they cannot cross cell membranes

Question 10

Which organ metabolises neuromuscular blocking drugs?

Answer 10

Liver

Question 11

Which organs excrete neuromuscular blocking drugs?

Answer 11

Kidneys

Question 12

How should neuromuscular blocking drugs be administered?

Answer 12

Neuromuscular blocking drugs should only be administered intravenously (I.V.)

Question 13

Why is it so important to make sure patients are breathing completely on their own before taking them off of mechanical ventilation following the use of neuromuscular blocking drugs?

Answer 13

The intercostal muscles and the diaphragm are resistant to neuromuscular blocking drugs, however, the muscles controlling the airway are very sensitive so it is possible for the patient to begin breathing again as the relaxant wears off but not be able to maintain a patent airway

Question 14

(T/F) Neuromuscular blocking drugs can cross the blood brain barrier

Answer 14

FALSE. Neuromuscular blocking drugs have a very low volume of distribution (Vd) and thus cannot cross the blood brain barrier

Question 15

Why is it safe to use neuromuscular blocking drugs during a caesarian section?

Answer 15

Neuromuscular blocking drugs have a low volume of distribution (Vd) so cannot cross the placenta, making them safe to use during caesarian sections

Question 16

List three ways neuromuscular blocking drugs can be used to improve surgical conditions

Answer 16

Facilitate endotracheal intubation
Relax skeletal muscle for easier surgical access
Stabilise the eye during ophthalmic surgery

Question 17

Which type of drug can be used to reverse the effects of neuromuscular blocking drugs?

Answer 17

Anticholinesterases

Question 18

How do anticholinesterases reverse the effects of neuromuscular blocking drugs?

Answer 18

Anticholinesterases inhibit acetylcholinesterase enzymes which break down acetylcholine, increasing the amount of acetylcholine at the neuromuscular junction, thus overcoming the effects of any residual neuromuscular blocking agent

Question 19

Why should you co-administer antimuscarinic drugs with anticholinesterase drugs?

Answer 19

To help reduce the side effects of excessive cholinergic stimulation caused by anticholinesterases

Question 20

What is sugammadex?

Answer 20

Sugammadex is a chemical antagonist used to reverse the neuromuscular blocking drugs

Question 21

Why does sugammadex not require antimuscarinic co-administration?

Answer 21

Sugammadex is a chemical antagonist which encapsulates the neuromuscular blocking drug to prevent it from binding to the nicotinic acetylcholine receptors at the neuromuscular junction. Since this drug only targets the neuromuscular blocking drug, it doesn’t interfere with any other receptors in the body

Question 22

Why is sugammadex not commonly used?

Answer 22

Sugammadex is very expensive

Question 23

How can general anaesthetics affect neuromuscular blocking drugs?

Answer 23

General anaesthesia can often potentiate the effects of neuromuscular blocking drugs

Question 24

How can antibiotics affect neuromuscular blocking drugs?

Answer 24

Certain antibiotics inhibit calcium influx at the axon terminal and thus inhibit the release of vesicles containing acetylcholine into the neuromuscular junction. This results in there being less acetylcholine available to stimulate muscle contraction as well as compete with the neuromuscular blocking drugs to bind to the nicotinic acetylcholine receptors, resulting in a prolonged effect of the neuromuscular blocking drugs

Question 25

Give an example of an antibiotic with prolongs the effects of neuromuscular blocking drugs

Answer 25

Aminoglycosides

Question 26

Which disease causes individuals to be much more sensitive to neuromuscular blocking drugs?

Answer 26

Myasthenia gravis