Local Anesthetic

 

Local Anesthetics

• definition

  drug to prevent the transmission of nerve impulse, without effect consciusness

  Local anesthetics (LAs) are drugs that block the sensation of pain in the region where they are administered. LAs act by reversibly blocking the sodium channels of nerve fibers, thereby inhibiting the conduction of nerve impulses. Nerve fibers which carry pain sensation have the smallest diameter and are the first to be blocked by LAs. Loss of motor function and sensation of touch and pressure follow, depending on the duration of action and dose of the LA used.

• how?

  reversibly blocking the movement of sodium inside in the nerve axon required for action potential

  When propagation of nerve impulse is prevented, the there can be no sensation/ impulse reaching the CNS/brain

• Mechanism of Action

  

  LA reversibly blocks the movement sodium in and out of the cell at the region where LA area applied

  Without sodium, there can be no nerve depolarization hence no action potentials propagate

  Lack of action potentials implies loss of sensation which include painful sensation

• Effect

  • Pain pathway
  • Local anesthetics (LA) bind to voltage-gated sodium channels of the nerve fibers → reversible blockage of sodium channels → inhibition of nerve excitation and impulse conduction (pain signals) → local anesthesia in the area supplied by the nerve
  • Nerve fibers have different degrees of susceptibility to LA, depending on their size and myelination
  • Factors which affect the efficacy of LA

• Component

  • A lypophylic/ hydrophobic aromatic compound
  • An intermediate chain which can either ester or amide
  • A hydrophilic amine

• Types

  • Ester - Procaine
  • Amides- Lidocaine

  

  Ester LAs do not have an “i” in their names preceding “-caine.” Amide LAs have an "i" in their name preceding “-caine.”

• Composition

  • Vasoconstrictor
  • Local Anesthetics Drug
  • Reducing agent
  • Preservative
  • Fungicide
  • Isotonic Solution

• Side Effect

  • Complications are uncommon
  • Allergy
  • Vasovagal syncope
  • Systemic toxicity

• Indications

  • Topical application (lidocaine, tetracaine, prilocaine)
  • Infiltration