LOCAL ANESTHETICS

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LOCAL ANESTHETICS

• Citation Dr. Walters note packet.

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• What is the mechanism of action for local
  anesthetics?
• Block voltage dependent Na channels (binds site
  inside alpha subunit)
• Local anesthetics preferentially bind to open and
  inactivated states. Binding to preferred states
  is called state dependence.

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• What is the clinical relevance of state
  dependence?
• Neurons that fire more often are in the preferred
  state more often, therefore they are more
  susceptible to local anesthetics.

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• What are the 2 categories of local anesthetics?
• Esters and amides.
• Esters metabolized by plasma esterases, shorter
  acting.
• Amides metabolized by liver, longer acting.

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ESTER LOCAL ANESTHETICS

• PROCAINE
• Short acting.
• Infiltration anesthesia injecting directly into
  operative area without regard to specific
  locations of nerves.
• Diagnostic nerve blocks injecting around a
  specific nerve or plexus.
• Diagnostic spinal anesthesia intrathecal at
  lumbar level (blocks sensory and motor fibers
  below diaphragm).

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• How do you control the spread of anesthetic
  within the subarachnoid space?
• Adjust specific gravity of solution hyperbaric,
  hypobaric
• Adjust tilt of patient.
• Toxic systemic effects and mech
• Respiratory depression, an extension of
  therapeutic effect (block Na channels).

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• CHLOROPROCAINE
• Rapid onset, short duration decrease toxicity.
• Epidural associated with increased incidence of
  MUSCULAR BACK PAIN possibly from tetany due to
  chelation of Ca by the preservative EDTA

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• COCAINE
• Intermediate acting
• Limited to topical use on mucous membranes.
• Advantage VASOCONSTRICTOR
• What is the mech of cocaine?
• Blocks NE uptake (also DA uptake)

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• What are 3 advantages of COCAINE?
• Decrease bleeding
• Increase duration of action
• Decrease systemic side effects
• How can you get this effect with other local
  anesthetics?
• By adding epi.
• Caution the vasoconstriction can slow wound
  healing and lead to tissue hypoxia and necrosis

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• What are 5 systemic effects of COCAINE?
• Euphoria mech blocks DA uptake
• Tremors and convulsions mech perhaps an
  increase in excitatory tone
• Respiratory depression and death mech blocks
  Na channels
• Tachycardia and vasoconstriction increase HR
  BP mech blocks NE uptake
• Hyperpyrexia mech block NE uptake
• How does vasoconstriction contribute to
  hyperpyrexia? Cannot dissipate heat.

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• TETRACAINE
• Long acting
• Problem cardiotoxic 1) slows the conduction
  thru the AV node 2) depression of contractility
• Mech of toxicity
• Blocks Na channels
• Caution vasodilates mech
• blocks Ca channels
• What is the concern?
• Increase systemic absorption

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• PROPARACAINE
• Ophthalmic
• Ester and ether link. It does NOT exhibit
  cross-sensitivity to other esters.

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AMIDE LOCAL ANESTHETICS

• LIDOCAINE
• Intermediate acting
• Faster onset and longer acting than procaine
• 2 active metabolites
• Mech for treating ventricular arrhythmia
• Anti arrhythmic agent

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• PRILOCAINE
• Dental cartridges only
• Intermediate acting
• Systemic toxicity (met-hemoglobinemia)
• Tx methylene blue

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• BUPIVACAINE
• Long acting
• With or w/o epi
• Can be cardiotoxic

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• LEVOBUPIVACAINE
• Long acting
• Isomer of bupivacaine

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• ETIDOCAINE
• Long acting
• Significant effect on MOTOR NEURONS provides
  good skeletal m. relaxation.

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• ROPIVACAINE
• Long acting
• Use during labor

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MISC.- FOR TOPICAL USE ONLY

• DIBUCAINE
• Amide
• Cream, ointment
• DYCLONINE
• 2 ether linkages
• Uses anesthetize mucous membranes prior to
  ENDOSCOPIC PROCEUDRES
• PRAMOXINE
• 2 ether links

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• BENZOCAINE
• Identical to procaine, but w/o amino group.
• What is the significance of this?
• Not water soluble
• BUTAMBEN
• OTC for mucous membranes, mouth sores

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OTHER LESS OBVIOUS LOCAL ANESTHETICS (ANALGESIA)

• OPIOIDS
• Morphine, epidural or intrathecal
• ABSOLUTE ETHANOL
• Injected near nerve trunks for intractable pain
  associated w/ cancer or trigeminal neuralgia.