Pharmacology  ·  Neuromuscular Blocking Drugs

Succinylcholine — Pharmacology Summary

Mechanism, duration, and three categories of serious adverse effect

Abbreviations: RSI = rapid sequence intubation  ·  MH = malignant hyperthermia  ·  K⁺ = potassium  ·  RyR = ryanodine receptor  ·  SR = sarcoplasmic reticulum  ·  ETCO₂ = end-tidal carbon dioxide

Depolarizing Agent
Drug Profile
  • Nicotinic receptor agonist — persistent depolarization
  • Fasciculations then flaccid paralysis
  • Onset: 60 seconds (fastest of all agents)
  • Duration: 5–10 minutes (normal enzyme)
  • Metabolized by plasma cholinesterase (pseudocholinesterase)
  • Not reversed by anticholinesterases
  • Use: rapid sequence intubation
Contraindication
Hyperkalemia Risk
  • Extrajunctional receptor upregulation → massive potassium efflux
  • Risk conditions: burns, crush injury, denervation, prolonged immobilization
  • Risk onset: after first 24–48 hours post-injury
  • Can cause ventricular fibrillation and cardiac arrest
  • Pseudocholinesterase deficiency: prolonged apnea, no reversal
Pharmacogenetic Crisis
Malignant Hyperthermia
  • Triggers: succinylcholine + volatile anesthetics
  • Defect: ryanodine receptor → uncontrolled calcium release
  • Signs: rising CO₂, rigidity, hyperthermia, acidosis
  • Treatment: dantrolene immediately; discontinue triggers
  • History of susceptibility: absolute contraindication
Critical Principle

Succinylcholine phase I block has no reversal agent. Anticholinesterase drugs (neostigmine) would worsen and prolong the block. Management of prolonged block — whether from pseudocholinesterase deficiency or any other cause — is mechanical ventilation until succinylcholine is cleared.

Suggested References

Author / Organization Title Source
Katzung BG (ed) Basic and Clinical Pharmacology, 15th ed. Chapter 27: Skeletal Muscle Relaxants McGraw-Hill, 2021
Brunton LL, Knollmann BC (eds) Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed. Chapter 12: Neuromuscular Blocking Agents McGraw-Hill, 2023
Martyn JAJ, Fagerlund MJ, Eriksson LI Basic principles of neuromuscular transmission Anaesthesia. 2009;64(Suppl 1):1–9
Richtsfeld M, Bhatt SB, Bhatt RD Succinylcholine-induced hyperkalemia in acquired pathologic states Anesthesiology. 2006;104(1):158–69
Larach MG, Gronert GA, Allen GC, et al Clinical presentation, treatment, and complications of malignant hyperthermia in North America from 1987 to 2006 Anesth Analg. 2010;110(2):498–507
Rosenberg H, Pollock N, Schiemann A, et al Malignant hyperthermia: a review Orphanet J Rare Dis. 2015;10:93
Viby-Mogensen J Succinylcholine neuromuscular blockade in subjects homozygous for atypical plasma cholinesterase Anesthesiology. 1981;55(4):429–34