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Drug Reference

succinylcholine

depolarizing neuromuscular blocker· Brands: Anectine, Quelicin, ScolineIMIV

Mechanism of action
Succinylcholine is a depolarizing neuromuscular blocker. It binds to nicotinic acetylcholine receptors on the motor endplate and acts as an agonist, causing persistent depolarization. This initial depolarization produces transient muscle fasciculations, followed by flaccid paralysis because the endplate cannot repolarize while the drug remains bound. Unlike non-depolarizing blockers, its action is not reversed by acetylcholinesterase inhibitors, which may worsen the block. It is metabolized by plasma cholinesterase (butyrylcholinesterase), not by acetylcholinesterase at the neuromuscular junction.
Pharmacokinetics
After intravenous injection, succinylcholine has a rapid onset of action, typically 30 to 60 seconds, and a short duration of paralysis, usually 5 to 10 minutes. It is hydrolysed by plasma cholinesterase to succinylmonocholine, which has weak neuromuscular blocking activity, and then more slowly to succinic acid and choline. The drug is also metabolised by hepatic cholinesterase. Metabolites are excreted renally. The duration of action is prolonged in patients with reduced or atypical plasma cholinesterase activity, which may be genetic, or acquired in liver disease, malnutrition, pregnancy, burns, or malignancy. There is no significant renal excretion of unchanged drug.
Indications & dosing

Rapid sequence induction and endotracheal intubation in adults

Give after induction agent and pre-oxygenation. Onset 30 to 60 seconds, duration about 5 to 10 minutes. Pre-treat with an antimuscarinic in children or where bradycardia is likely.

  • adult · IV: 1–1.5 mg/kg single dose · Give after induction agent and pre-oxygenation. Onset 30 to 60 seconds, duration about 5 to 10 minutes. Pre-treat with an antimuscarinic in children or where bradycardia is likely.

Endotracheal intubation in children

Children need a higher weight-based dose than adults. Give atropine or glycopyrronium beforehand to reduce the risk of bradycardia and asystole, especially on repeat dosing.

  • pediatric · IV: 1.5–2 mg/kg single dose · Children need a higher weight-based dose than adults. Give atropine or glycopyrronium beforehand to reduce the risk of bradycardia and asystole, especially on repeat dosing.

Endotracheal intubation when intravenous access is not available

Intramuscular route gives slower onset (2 to 4 minutes) and longer duration. Total dose should not exceed 150 mg. Use the deltoid or thigh to speed absorption.

  • adult · IM: 3–4 mg/kg single dose · Intramuscular route gives slower onset (2 to 4 minutes) and longer duration. Total dose should not exceed 150 mg. Use the deltoid or thigh to speed absorption.

Treatment of laryngospasm during anaesthesia

Reserve for laryngospasm that persists after jaw thrust, positive pressure and deepening of anaesthesia. Small doses may be effective in children at the lower end of the range.

  • adult · IV: 0.5–1 mg/kg single dose · Reserve for laryngospasm that persists after jaw thrust, positive pressure and deepening of anaesthesia. Small doses may be effective in children at the lower end of the range.

Muscle relaxation for electroconvulsive therapyoff-label

Given immediately before the seizure stimulus to limit motor convulsion and musculoskeletal injury. Dose is titrated to the patient; premedication with an antimuscarinic reduces secretions and bradycardia.

  • adult · IV: 0.5–1 mg/kg single dose · Given immediately before the seizure stimulus to limit motor convulsion and musculoskeletal injury. Dose is titrated to the patient; premedication with an antimuscarinic reduces secretions and bradycardia.

Maintenance of neuromuscular relaxation during short procedures

Intermittent boluses only; repeated or infusion dosing causes phase II block and prolonged paralysis. Adequacy should be judged with a peripheral nerve stimulator. Avoid by infusion wherever possible.

  • adult · IV: 0.1–0.2 mg/kg as required · Intermittent boluses only; repeated or infusion dosing causes phase II block and prolonged paralysis. Adequacy should be judged with a peripheral nerve stimulator. Avoid by infusion wherever possible.
Contraindications & precautions
  • Known or suspected malignant hyperthermia susceptibility (personal or family history) · Succinylcholine is a potent triggering agent. Use a trigger-free anaesthetic technique with a non-depolarising blocker instead.
  • Known or suspected pseudocholinesterase (butyrylcholinesterase) deficiency or previous prolonged apnoea after succinylcholine · Atypical enzyme variants or acquired deficiency cause profoundly prolonged paralysis. If given in error, ventilate and sedate until recovery; arrange genotyping and family screening.
  • Hyperkalaemia, or conditions that predispose to it: burns, crush injury, spinal cord injury, denervation, prolonged immobility, severe sepsis, metabolic acidosis · Extrajunctional receptor upregulation can release enough potassium to cause cardiac arrest. Risk starts roughly 24 to 48 hours after the insult and persists for months.
  • Skeletal muscle myopathy, including Duchenne muscular dystrophy and other undiagnosed myopathies · Risk of hyperkalaemic cardiac arrest and rhabdomyolysis. In children reserve the drug for emergency intubation where a myopathy may be present but undiagnosed.
  • Previous anaphylaxis or severe hypersensitivity reaction to succinylcholine · Cross-reactivity with other quaternary ammonium neuromuscular blockers is possible; take allergy history carefully before any re-exposure.
  • Penetrating eye injury or raised intraocular pressure · Transient rise in intraocular pressure occurs, but the benefit of rapid airway control in a full stomach usually outweighs this small theoretical risk. Decision rests with the anaesthetist.
  • Severe hepatic failure or organophosphate exposure (acquired cholinesterase deficiency) · Reduced enzyme activity prolongs blockade. Use a reduced dose with quantitative neuromuscular monitoring, or choose a non-depolarising agent.
  • Give only to an unconscious patient, with secured IV access and continuous ECG, pulse oximetry, capnography and temperature monitoring. Neuromuscular monitoring is used for repeated or prolonged dosing.
  • Ensure immediate access to a difficult airway trolley, suction and dantrolene before administration, because profound apnoea is expected and malignant hyperthermia is a rare but treatable complication.
  • Have atropine or glycopyrronium drawn up. Consider anticholinergic premedication in children and where a second dose is anticipated, since bradycardia is more likely.
  • Avoid repeated doses where an alternative exists. Tachyphylaxis, phase II block and bradycardia become more likely with each dose.
  • Stop the drug and call for help if masseter spasm, generalised rigidity or an unexplained rise in end-tidal carbon dioxide appears. Treat as suspected malignant hyperthermia and start dantrolene.
  • Review concurrent drugs that reduce cholinesterase activity (neostigmine, organophosphates, cyclophosphamide, some oestrogens, monoamine oxidase inhibitors) and store the product at 2 to 8 degrees Celsius as directed by the label.
Adverse effects
  • Muscle fasciculations, visible in most patients after injection
  • Postoperative muscle pains and raised creatine kinase
  • Bradycardia or junctional rhythm, particularly in children and after a second dose
  • Transient rise in intraocular and intragastric pressure
  • Malignant hyperthermia: rising end-tidal carbon dioxide, rigidity, hyperthermiaserious
  • Hyperkalaemia with cardiac arrest, especially in burns, crush injury or denervationserious
  • Prolonged paralysis and apnoea in pseudocholinesterase deficiencyserious
  • Anaphylaxisserious
  • Masseter muscle rigidity and rhabdomyolysisserious
Renal & hepatic adjustment
  • eGFR 30+: No specific dose adjustment. Use with caution and monitor neuromuscular function and potassium, as renal impairment may reduce plasma cholinesterase activity and prolong block.
  • eGFR 15–29: Use with caution. Risk of prolonged block and hyperkalaemia is increased. Consider an alternative non-depolarising agent if potassium is elevated.
  • eGFR 0–14: Avoid in severe renal impairment (eGFR below 15) due to risk of life-threatening hyperkalaemia. If use is unavoidable, reduce dose and monitor potassium and neuromuscular block closely. (avoid)
  • Hepatic impairment (mild): No specific dose adjustment. Monitor for prolonged neuromuscular blockade as hepatic impairment may reduce pseudocholinesterase activity.
  • Hepatic impairment (moderate): No specific dose adjustment, but reduced pseudocholinesterase may prolong block. Use nerve stimulation monitoring and consider a reduced dose.
  • Hepatic impairment (severe): Use with caution or avoid if possible. Severe liver disease can markedly reduce pseudocholinesterase and increase the risk of prolonged apnoea. If used, reduce dose and monitor neuromuscular function closely.
Monitoring, pregnancy & toxicity
  • Neuromuscular function using train-of-four or peripheral nerve stimulator · Before, during, and after administration until full recovery
  • Respiratory status including oxygen saturation, end-tidal carbon dioxide, and tidal volume · Continuous during and after administration until full recovery
  • Plasma potassium · Baseline and shortly after administration in at-risk patients, such as those with renal failure, burns, trauma, or denervation
  • Body temperature and signs of malignant hyperthermia · Continuous during and after administration
  • Cardiac rhythm and heart rate · Continuous, especially in children and after repeated doses, due to risk of bradycardia
  • Signs of anaphylaxis such as hypotension, bronchospasm, rash, and angioedema · Continuous during and after administration
  • Pregnancy: Succinylcholine may be used in pregnancy when rapid sequence induction is required. It crosses the placenta, but fetal effects are usually minimal. Plasma cholinesterase activity is reduced in pregnancy, so monitor for prolonged neuromuscular blockade. Use the minimum effective dose and follow local obstetric anaesthesia protocols.
  • Toxicity: Prolonged apnoea and muscle paralysis after a standard dose, due to pseudocholinesterase deficiency or reduced enzyme activity from pregnancy, liver disease, or renal failure. · Continue mechanical ventilation and sedation until recovery. Monitor neuromuscular function. Avoid further succinylcholine. Recovery may take hours; consider non-depolarising agent if ongoing paralysis is needed.
  • Toxicity: Malignant hyperthermia: hyperthermia, muscle rigidity, tachycardia, hypercapnia, rhabdomyolysis, and metabolic acidosis. · Stop succinylcholine and all triggering agents. Give dantrolene, active cooling, and supportive care. Monitor for complications such as renal injury and coagulopathy.
  • Toxicity: Acute hyperkalaemia with peaked T waves, arrhythmias, and cardiac arrest, especially in patients with renal failure, burns, denervation, or trauma. · Stop succinylcholine. Treat hyperkalaemia urgently with calcium, insulin and dextrose, bicarbonate, and dialysis as needed. Monitor ECG and potassium closely.
  • Toxicity: Anaphylaxis with hypotension, bronchospasm, rash, and angioedema. · Stop the drug. Give adrenaline intramuscularly, fluids, oxygen, antihistamines, and corticosteroids according to local anaphylaxis protocols.
Clinical notes
Succinylcholine is used for rapid sequence induction and short procedures requiring muscle relaxation, such as tracheal intubation and electroconvulsive therapy. It is given intravenously, with intramuscular use when intravenous access is not available. It can cause hyperkalaemia, especially in patients with burns, crush injuries, spinal cord injury, or neuromuscular disease, and should be avoided in these groups. Other adverse effects include malignant hyperthermia, bradycardia (particularly in children), raised intraocular and intragastric pressure, and prolonged paralysis in pseudocholinesterase deficiency. It is contraindicated in known malignant hyperthermia susceptibility and in patients with penetrating eye injuries. Doses are teaching examples only: intravenous 1 to 1.5 mg/kg, intramuscular 3 to 4 mg/kg, though practice varies by region and formulary. Premedication with atropine or glycopyrrolate may be used in children to prevent bradycardia. Always verify against local protocols and current prescribing information.

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BNF; local formulary; summary of product characteristics