PHARMACOLOGY - Neuromuscular Blocking Drugs Flashcards
What is the mechanism of action for neuromuscular blocking drugs?
Neuromuscular blocking drugs are competitive antagonists for nicotinic acetylcholine receptors at the neuromuscular junction
What is the general structure of neuromuscular blocking drugs?
Rigid, bulky molecules with a central quaternary nitrogen
What is the desired affect of neuromuscular blocking drugs?
Flaccid motor paralysis
Why are neuromuscular blocking drugs only given after the patient is under general anaesthesia?
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
What are the two last muscles to be affected by neuromuscular blocking drugs?
Intercostal muscles
Diaphragm
What are the two main adverse affects of neuromuscular blocking drugs?
Hypotension
Tachycardia
How do neuromuscular blocking drugs cause hypotension?
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
How do neuromuscular blocking drugs cause tachycardia?
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
Why are neuromuscular blocking drugs incapable of crossing cell membranes?
The central quaternary nitrogen makes neuromuscular blocking drugs inherently charged and thus they cannot cross cell membranes
Which organ metabolises neuromuscular blocking drugs?
Liver
Which organs excrete neuromuscular blocking drugs?
Kidneys
How should neuromuscular blocking drugs be administered?
Neuromuscular blocking drugs should only be administered intravenously (I.V.)
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?
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
(T/F) Neuromuscular blocking drugs can cross the blood brain barrier
FALSE. Neuromuscular blocking drugs have a very low volume of distribution (Vd) and thus cannot cross the blood brain barrier
Why is it safe to use neuromuscular blocking drugs during a caesarian section?
Neuromuscular blocking drugs have a low volume of distribution (Vd) so cannot cross the placenta, making them safe to use during caesarian sections
List three ways neuromuscular blocking drugs can be used to improve surgical conditions
Facilitate endotracheal intubation
Relax skeletal muscle for easier surgical access
Stabilise the eye during ophthalmic surgery
Which type of drug can be used to reverse the effects of neuromuscular blocking drugs?
Anticholinesterases
How do anticholinesterases reverse the effects of neuromuscular blocking drugs?
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
Why should you co-administer antimuscarinic drugs with anticholinesterase drugs?
To help reduce the side effects of excessive cholinergic stimulation caused by anticholinesterases
What is sugammadex?
Sugammadex is a chemical antagonist used to reverse the neuromuscular blocking drugs
Why does sugammadex not require antimuscarinic co-administration?
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
Why is sugammadex not commonly used?
Sugammadex is very expensive
How can general anaesthetics affect neuromuscular blocking drugs?
General anaesthesia can often potentiate the effects of neuromuscular blocking drugs
How can antibiotics affect neuromuscular blocking drugs?
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
