Question 10

College Answer

This commonly used drug should be very well-known. The question asked for an outline, hence long explanations of various aspects of pharmacology (e.g. pseudocholinesterase deficiency) were unnecessary. Headings should have included:  advantages (e.g. rapid onset, rapid offset, short acting, IV or IM administration, not end organ dependent for metabolism, premixed, safe in pregnancy and neonates). The  disadvantages section should have included the following headings: pharmaceutical, adverse drug reactions (including several potentially fatal ones), numerous contraindications, unpleasant side-effects and potential problems with repeat dosing

Discussion

Advantages:

• Rapid onset (fastest acting NMJB agent)
• Rapid offset, an advantage for:
  • electroconvulsive therapy
  • cardioversion
  • short ENT procedures
  • for the reduction of fractures.
• Organ-independent metabolism:  suxamethonium is metabolised by plasm pseudocholinesterase
• Safety in pregnancy and in neonates is mentioned as an advantage, though it also must be pointed out that many other NMJ blockers are also considered safe in pregnancy, and basically all of them are considered safer than an unprotected airway for a pregnant patient
• Cost is an advantage. Suxamethonium is among the cheapest NMJ blockers available.
• Pre-mixed should be listed as an advantage, mainly to increase the length of the list

Disadvantages:

• Pharmacokinetic:
  • Pseudocholinesterase may be deficient in the critically ill (eg. liver failure)
• Pharmacodynamic:
  • ​​​​​​​Unsuitable for sustained NMJ blockade; tachyphylaxis, Phase II block and self-antagonism with sustained use
• Adverse effects
  • ​​​​​​​Masseter spasm
  • Autonomic side effects: bradycardia OR tachycardia
  • Increased intraocular pressure
  • Increased intragastric pressure
  • Increased intracranial pressure
  • Fasciculations
  • Myalgia
  • Hyperkalemia
• Contraindications
  • Spinal injury
  • Stroke
  • Burns
  • Denervation
  • Prolonged immobility
  • Critical illness (ICU-associated weakness)

Lee, Chingmuh. "Suxamethonium in its fifth decade." Baillière's clinical anaesthesiology 8.2 (1994): 417-440.

Lee, C. "Goodbye suxamethonium!." Anaesthesia 64 (2009): 73-81.

Gibb, David B. "Suxamethonium—A Review: Part I.—Physico-Chemical Properties and Fate in the Body." Anaesthesia and Intensive Care 1.2 (1972): 109-118.

Gibb, David B. "Suxamethonium—A Review: Part II—Neuromuscular Blocking Properties." Anaesthesia and Intensive Care 1.3 (1973): 183-201.

Gibb, David B. "Suxamethonium-A Review: Part III—Pharmacological Actions of Suxamethonium Apart from Its Neuromuscular Blocking Effect." Anaesthesia and Intensive Care 2.1 (1974): 9-26.

Torda, T. A., et al. "Pharmacokinetics and pharmacodynamics of suxamethonium." Anaesthesia and intensive care 25.3 (1997): 272-278.