Suxamethonium

Question 1

What is suxamethonium used for?

Answer 1

Rapid sequence intubation (fast onset relaxation 45s)

Question 2

What is the MOA of suxamethonium?

Answer 2

• binds to alpha subunit of nicotinic receptors at NMJ causing chaotic depolarisation of muscle, therefore fasciculation occurs then paralysis
• not broken down by ACh-ase and more stable than endogenous ACh so occupies receptor for longer maintaining relaxation
• broken down by pseudocholinesterase in plasma after diffusing away from synaptic cleft

Question 3

What % of suxamethonium reaches the NMJ?

Answer 3

only 20% due to rapid hydrolysis

Question 4

What are the SEs of suxamethonium?

Answer 4

• may cause arrhythmias by binding to muscarinic receptors - sinus and nodal bradycardia and ventricular ectopics
• anaphylaxis
• MH
• release of K from cells causing hypercalaemia, esp in burns patients, effect can persist from 24hrs to 2years post injury
• myalgia
• increased IOP
• increased intragastric pressure and LOS pressure
  
  • prolonged neuromuscular blockade with repeated dosing (TYPE 2 block = shows fade on TOF but can’t be reversed by neostigmine)

Question 5

What is suxamethonium and what is the dose?

Answer 5

Depolarising neuromuscular blocker. Store at 4 degrees celcius.

Dose 1-2 mg/kg

Question 6

What are the chemical properties of suxamethonium?

Answer 6

• 2 acetylcholine molecules joined together by acetyl groups
• white crystalline substance very soluble in water
• ph of solution = 4

Question 7

What is the metabolism and excretion of suxamethonium?

Answer 7

• diffuses away from synaptic cleft and metabolised by plasma cholinesterases (pseudocholinesterase)
• hydrolysed to choline and succinylmonocholine
• latter metabolised to succinic acid and choline