LOCAL ANESTHETICS

• Local Anesthesia


  Loss of sensation in a body part without the loss of consciousness or the impairment of central control of vital functions
• Types of Local Anesthetics

  • Esters
  • Amides
• Esters


  • Only 1 letter "i" in its name
• Benzoic acid derivatives (Esters)


  • Cocaine
  • Hexylcaine
  • Meprylcaine
  • Isobucaine
  • Cyclomethicaine
  • Piperocaine
• Para-aminobenzoic acid (PABA) derivatives (Esters)


  • Procaine
  • Propoxycaine
  • Benzocaine
  • Proparacaine
  • Chlorprocaine
  • Tetracaine
  • Butacaine
  • Benoxinate
• Amides


  • 2 letter "i" in its name
• Amide Agents


  • Lidocaine
  • Mepivacaine
  • Bupivacaine
  • Etidocaine
  • Articaine
  • Ropivacaine
  • Prilocaine
• Esters are subject to hydrolysis by the plasma esterases
• Hypersensitivity is rare but commonly seen with esters, particularly PABA derivatives
• Cocaine


  Blocks conduction of nerve impulses and causes local vasoconstriction
• Cocaine is not very useful clinically because of its abuse potential and toxicity</b>
• Procaine


  First synthetic local anesthetic, limited use because of its low potency, slow onset, and short duration of action
• Lidocaine (Xylocaine)


  Most widely used local anesthetic, produces faster, more intense, longer-lasting, and more extensive anesthesia than procaine
• Bupivacaine


  Potent agent capable of producing prolonged anesthesia, can be given as continuous infusion for providing prolonged anesthesia during labor or the post-operative period
• Tetracaine


  More potent and has longer duration of action than procaine, more slowly metabolized than other ester local anesthetic thus has increased toxicity
• Chlorprocaine


  Rapid onset and short duration of action, reduced systemic toxicity due to rapid metabolism (plasma half-life = 25 seconds)
• Etidocaine


  Long-acting, with onset of action faster than bupivacaine and comparable to that of lidocaine, provides preferential motor blockade (very useful in surgery requiring intense skeletal muscle relaxation but limited use in labor or postoperative analgesia)
• Mepivacaine


  Intermediate-acting, pharmacological properties similar to lidocaine but more toxic to the neonate, so not used in obstetrics
• Mepivacaine has a higher therapeutic index in adults than lidocaine
• Mepivacaine is not useful as a topical anesthetic
• Prilocaine


  Lidocaine-like pharmacological profile but a.) causes little vasodilation thus can be used without a vasoconstrictor, and b.) has increased volume of distribution reducing its CNS toxicity (thus suitable for intravenous regional block)
• Methemoglobinemia caused by prilocaine is treatable with 1-2 mg/kg dose of methylene blue