Succinylcholine (aka “sux”) is a depolarizing muscle relaxant that produces the tell-tale fasciculations at onset of action.
It is commonly used in intubation and has a fast onset of action of 30-60 seconds and a short duration of action of 10-15 minutes.
Practitioners must be familiar with the possible adverse effects of this drug. These include bradycardia through its parasympathetic/muscarinic effect and sometimes an idiosyncratic tachycardia through a sympathetic/nicotinic effect.
Most well-known is the side effect of raising serum potassium approximately 0.5 meq/L, making its use contraindicated in burns, crush injuries, denervating injuries, and myopathies.