Local Anesthetics


Considerations 

  • Local Anesthetics work on sodium channels as they block the entry of sodium.
  • Factors to consider while using local anesthetics (LA) is their onset time, potency and duration of action
  • Onset-  relies on the quantity of nonionized form of LA present. The higher the nonionized concentration of the drug, the easier it is for the LA to enter the nerve axon through the lipid bilayer.
  • Duration of Action- depends on protein binding and lipid solubility. Protein binding works similar in all drug. If you have a drug that is highly protein bound, it is released over a longer period of time as the free serum drug molecules are used. Albumin levels and alpha 1 glycoprotein can therefore alter duration of actions. Lipid solubility works in similar fashion as drug is bound to lipids instead of protein. However, as the free concentration of the drug decreases, the lipid bound drug molecules are slowly released overtime. This is the idea behind using lipids for local anesthetic toxicity.
  • Potency- also depends on lipid solubility to some degree.
  • LA toxicity signs & symptoms - Tinnitus, metallic taste, seizures, hypotension, respiratory and cardiac signs.
  • Lipid Emulsion 20% - 1.5 ml/kg initial bolus followed by continuous infusion of 0.25 to 0.5 ml/kg/min.
  • Use benzodiazepines to widen seizure threshold and secure airway.


Common Clinical Question
  • Cocaine has vasoconstrictive properties and is naturally acting