Suxamethonium 💊
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💉 Suxamethonium (succinylcholine) is the classic depolarising muscle relaxant used for rapid sequence induction (RSI).
It has a very rapid onset and short duration of action, making it ideal for airway control in emergencies.
⚠️ However, its use carries important risks including hyperkalaemia, malignant hyperthermia, and suxamethonium apnoea.
📖 About
- Always check the BNF link here for up-to-date prescribing advice.
- Depolarising neuromuscular blocker, metabolised by plasma pseudocholinesterase.
⚙️ Mode of Action
- Binds to the nicotinic acetylcholine receptor at the neuromuscular junction → persistent depolarisation → paralysis.
- Not broken down by acetylcholinesterase at the synapse, leading to sustained block.
- Metabolised by plasma pseudocholinesterase in the circulation.
💊 Indications/Dose
| Name | Starting Dose | Frequency | Route |
|---|
| Suxamethonium | 1.5–2 mg/kg | Single dose | IV |
⏱️ Action
- Fasciculations in 5–15 seconds.
- Complete paralysis in 45–60 seconds.
- Return of spontaneous breathing: 5–10 minutes.
🔗 Interactions
- See BNF for full list (interactions with anaesthetic agents, certain antibiotics, and anticholinesterases).
⚠️ Cautions
- Raises serum potassium by ~0.5 mmol/L → dangerous in patients with baseline hyperkalaemia.
- Use with caution in renal failure, neuromuscular disorders, burns, severe trauma, or sepsis.
- Bradycardia more likely in children and with repeated doses.
⛔ Contraindications
- Known pseudocholinesterase deficiency (risk of prolonged apnoea).
- Hyperkalaemia or conditions predisposing to it (burns, cord injury, severe sepsis, crush injuries).
- Personal or family history of malignant hyperthermia.
💥 Side Effects
- Hyperkalaemia and risk of cardiac arrest.
- Bradycardia, especially in children.
- Muscle fasciculations and postoperative myalgia.
- Histamine release → flushing, bronchospasm, hypotension.
- Malignant hyperthermia (rare but life-threatening).
- Suxamethonium apnoea: prolonged paralysis in patients with pseudocholinesterase deficiency.
📚 References
