• Need to know suxemethonium very well – important ED drug. Know PK, PD and toxic side effects.
  1. Suxemethonium’s chemical structure is essentially two ACh molecules bound together.
  1. Suxemethonium binds to the nicotinic receptor and activates it, causing depolarization of the motor end plate and spreading of the action potential.
    • However, it is not metabolized by true acetylcholinesterase at the NM junction, and therefore, repolarization cannot occur.
    • Since muscular contraction requires repetitive firing, a flaccid paralysis then occurs. The initial flaccid paralysis is known as phase I (depolarizing) block, and is further augmented by acetylcholinesterase inhibitors.
    • Prolonged exposure to suxemethonium causes a repolarization of the membrane, but it is not easily depolarized again. The membrane is said to be desensitized (phase II). The channel behaves as if it were blocked by non-depolarising agents and this phase may be reversed with acetylcholinesterase inhibitors.
    • Overall suxemethonium causes a paralysis in ~30s, affecting the arm, neck and leg muscles first before respiratory muscles.
  2. CVS effects of suxemethonium
    • Suxemethonium stimulates nicotinic receptors at the sympathetic and parasympathetic ganglia, as well as muscarinic receptors in the heart. This leads to negative inotropy and negative chronotropy. Administration of an anti-cholinergic medication concurrently may reduce the response.
    • A second dose of Sux within 5 minutes may also cause bradycardia.
  1. IV only
  1. Very polar – small Vd.
  1. Sux is broken down by plasma cholinesterase and bytyrylcholinesterase (pseudocholinesterase)
    • No/very little metabolism occurs at the NMJ.
    • The offset of action is due to Sux diffusing away from the NMJ.
    • Onset time is 30-45s (slower in low cardiac output states) and offset time is 8-10 minutes.
  1. Action terminated by diffusion
  1. RSI, due to rapid onset
  1. Hyperkalemia
    • Also CI in other conditions that may release K+, e.g. burns, nerve damage, neuromuscular disease, closed head injury.
  2. Pseudocholinesterase deficiency
  3. Open anterior chamber/globe rupture
Special precautions
  1. Halothane gas – cardiac arrhythmias


Adverse events
  1. Hyperkalemia
  2. Raised intra-ocular pressure (note that Sux is not an absolute CI unless the anterior chamber is open due to globe rupture)
  3. Increased intra-gastric pressure (higher risk of aspiration)
  4. Myalgia post-op
  5. Malignant hyperthermia
  1. 1mg/kg in adults
  2. 1-2mg/kg in paediatric population
Withdrawal syndrome
Special notes