0
Q
Structure
A
SCh consists of two ACh molecules joined together
1
Q
Mechanism of action
A
- SCh binds to the two α subunits of nicotinic cholinergic receptors in the same way as ACh, causing the ion channel to open
- This produces the muscle contractions known as fasiculations
- SCh remains bound to the subunits longer than ACh and is not metabolised by AChE. The ion channel therefore remains open for longer than when ACh binds
- The result is a sustained depolarisation of the end plate which prevents action potential propagation and causes muscle paralysis
3
Q
Onset and duration of action
A
Onset: 30-60 seconds Duration: 5-10 minutes
5
Q
Dosage
A
Intubating dose - 1mg/kg (adults) - 2mg/kg (infants)
6
Q
Contraindications
A
- Known malignant hyperthermia (MH) or family history of MH
- Previous anaphylaxis
- Risk of hyperkalaemia
- Major trauma
- Burns
- Prolonged immobility
- Spinal injury
- Denervation
- Sepsis/ infection
- Neurological or muscular diseases e.g. muscular dystrophies, severe Parkinson’s disease, tetanus, polyneuropathies etc
- Penetrating eye injuries
- Pre existing hyperkalaemia
- Pseudocholinesterase deficiency (homozygous atypical)
8
Q
Side effects
A
- Stimulation of cardiac muscarinic AChR
- Bradycardia
- AV node dysrhythmias
- Ventricular arrhythmias
- Depolarisation of the endplate
- Increased intracranial pressure
- Increased intraocular pressure
- Increased intragastric pressure
- Release of intracellular potassium - normally only 0.5-1 mmol/l, but may be much more
- Myalgia
- Masseter spasm
- Trigger of malignant hyperthermia
- Allergic reactions
9
Q
Metabolism
A
Metabolism: pseudocholinesterase
Reduced metabolism:
- Decreased enzyme levels – pregnancy, liver disease, renal failure
- Abnormal enzyme – scoline apnoea
- Decreased enzyme activity – hypothermia, drugs e.g. ecothiophate, cyclophosphamide, neostigmine, trimethaphan
Anesthetics
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