NMJ Blockers

Question 1

Name a drug that inhibits the centra process of movement

Answer 1

Diazepam- a spasmolytic that inhibits the generation of a nervous impulse in cortical cell bodies

Question 2

What do anaesthetics do? (In general)

Answer 2

Inhibit conduction of nervous impulses down motor neurones

Question 3

Name three drugs that inhibit Ach release at an NMJ

Answer 3

Neurotoxin, calcium channel blockers, hemicholinium

Question 4

What do tubocurarine and suxamethonium do? (In general)

Answer 4

Inhibit excitation of the ,toot end plate that would usually lead to AP generation

Question 5

What does dantrolene do and what is the consequence?

Answer 5

It is a ryanodine receptor antagonist and hence it inhibits the excitation- contraction coupling of skeletal muscle.

Question 6

How does suxamethonium work? (Three steps)
How does the body respond?
Route of action and break down

Answer 6

It is a depolarising NMJ blocker
It is broken down much more slowly than ACh, so causes extended end plate depolarisation, which leads to a depolarising block as receptors desensitise

The body will have fasiculations followed by flaccid paralysis (5 mins)
Administer IV (highly charged) and it is ,established by pseudo cholinesterase in the liver and plasma.

Question 7

Describe two uses and two unwanted effects of suxamethonium

Answer 7

Uses: as a muscle relaxant for endotracheal intubation and ECT
Unwanted effects: post op muscle pain, bradycardia (direct muscarinic effect on the heart), hyperkalaemia (especially in those with soft injuries, recpetors have been upregulated), increased intraocular pressure

Question 8

Who would you avoid giving suxamethonium to? (3)

Answer 8

Cardiac failure (bradycardia), soft tissue injury/burns patients (hyerkalaemia could lead to VF) and glaucoma (increases intraocular pressure)

Question 9

Three very important considerations for NMJ blockers

Answer 9

They don’t affect consciousness
They don’t affect pain sensation
But always need respiratory support

Question 10

What type of drug is tubocurarine? Can you think of another example?
How does the body respond- in general and specifically?

Answer 10

Is a tertiary a ammonium compound, otherwise known as an alkaloid. Used in arrow root poison. Pilocarpine ( direct cholinoceptor agonist)was also an alkaloid.
Body responds with flaccid paralysis. First the extrinsic eye muscles, leading to double vision, then the small muscles of the face, limbs and pharynx and lastly the respiratory muscles.

Question 11

Name two uses of tubocurarine?

Answer 11

Muscle relaxant administered with anaesthetic

To permit artificial respiration

Question 12

How would reverse the effects of tuburocurarine?

Answer 12

Give an anti cholinesterase like physostigmine

But with atropine, to prevent overstimulation of autonomic nAChRs

Question 13

Describe the administration, duration of action and excretion of tuburocurarine

Answer 13

Admits termed IV (highly charged), long duration of action of 40-60 minutes, NOR METABOLISED but 70% excreted by kidneys and 30% in bile

Question 14

Describe 5 unwanted effects of tubocurarine

Answer 14

Hypotension (from ganglia blockade, exacerbated by triggered histamine release from mast cells)
Tachycardia (as a reflex, but also possibly from bagel g alliance blockade)
Increased secretions (histamine)
Bronchi spasm (histamine)
Apnoea

Question 15

Describe 4 patients you would avoid giving tubocurarine to

Answer 15

Liver failure
Renal failure 
(Give atracurium instead, chemically unstable so is metabolised into two fragments IN THE PLASMA in just 15 mins) 
Postural syncope
Tachycardia
Asthmatic
COPD