Local anaesthetics

Classification

Ester LA’s

  1. Cocaine(first used LA)
  2. Procaine(LA of choice in malignant hyperthermia)
  3. chlorprocaine(Shortest acting)
  4. Tetracaine
  5. Benzocaine

Amide LA’s

  1. Lignocaine
  2. Prilocaine(Methemoglobinemia)
  3. Bupivacaine(Most cardiotoxic)
  4. Dibucaine(Longest acting)
  5. Mepivacaine
  6. Etidocaine
  7. Ropivacaine

Properties of LA’s

  • All LA’s are weak bases,so sodium bicarbonate speeds up the action of LA’s by increasing the unionized form.
  • LA’s act by blocking voltage gated sodium channels.
  • Vasoconstrictors like adrenaline prolong duration of action and decrease systemic toxicity.
  • Thin unmyelinated fibers are blocked first and thick myelinated fibres are blocked last.
  • Order of blockade is B, C ,Adelta,Aalpha, Abeta.
  • Autonomic>Sensory>Motor
  • Temperature(cold first)>Pain>Touch
  • Chlorprocaine is CI in spinal anaesthesia.
  • Dibucaine is most potent,longest acting and most toxic LA.
  • Bupivacaine is best for regional block,but it is the most cardiotoxic so should not be used in Biers block.
  • Prilocaine is most suitable for Biers block.
  • Lignocaine and Bupivacaine are used for spinal anaesthesia
  • Adrenaline should not be combined with LA’s when used on organs with end arteries(fingers,toes etc.)

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