Suxamethonium

Suxamethonium (Anectine, Succinylcholin)

Mechanism of action

Depolarising neuromuscular blocker (ultra-short-acting).

Phase 1 - Blocks neuromuscular transmission by binding to motor end-plate nicotinic acetylcholine receptors which causes depolarisation - fasciculations and then desensitisation after repolarisation – flaccid paralysis.

Phase 2: With prolonged exposure, initial end plate depolarisation decreases and membranes become repolarised. Membrane is desensitised and cannot easily be depolarised again

Indications and dose

Pharmacokinetics

Onset of action: 

Intravenous: 0.5–1 min

Intramuscular: 2–3 minutes

Duration of action: 

Intravenous: 4–6 min

Intramuscular: 10–30 min

Half-life of elimination: 

Intravenous: 47 seconds

Metabolism: Rapid hydrolysis by plasma cholinesterase, partly hepatic butyrylcholinesterase

Elimination: Kidneys (10 % unchanged drug)

Directions for administration

Powder – dilute in 5% glucose or 0.9% sodium chloride to provide 0.1% to 0.2% solution

Administer intravenously

Medicinal forms

Solution for injection/infusion (50 mg/ml)

1 vial = 2 ml (100 mg)

Powder for injection/infusion solution (100 mg)

1 vial = 100 mg

Side-effects

Cardiac – bradycardia, tachycardia, arrhythmias

Hyperkalaemia

Increased intraocular pressure

Increased intragastric pressure

Skin flushing

Post-operative muscle pain

Myoglobinaemia, myoglobinuria

Malignant hyperthermia

Bronchospasm

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Reversal

Anticholinesterase drugs are not antidotes to suxamethonium but would normally intensify the depolarisation effect.

The decision to use neostigmine to reverse a phase II suxamethonium-induced block depends on the judgement of the clinician in the individual case.

Transfusion of fresh whole blood, frozen plasma, or other source of pseudocholinesterase will help the destruction of suxamethonium.

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References

1. Pharm 101: Suxamethonium • LITFL • Top 200 Drugs
2. Suxamethonium Chloride 50mg/ml Solution for Injection - Summary of Product Characteristics (SmPC) - (emc) (medicines.org.uk)
3. Suxamethonium: Indication, Dosage, Side Effect, Precaution | MIMS Malaysia
4. Succinylcholine: Uses, Interactions, Mechanism of Action | DrugBank Online
5. Succinylcholine Monograph for Professionals - Drugs.com