Local Anesthetics

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Local Anesthetics
(general mechanism and side effects)

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Mechanism: Hydrophobic aromatic moiety permits diffusion thourgh membrane to to intracellular side of Na channel.
LAs block fast Na channels by slowing inactivation recovery.
Repeated LA injection -> local acidosis -> refractoriness
Distal areas anesthetize first and recover first
Analgesia precedes loss of other sensory and motor function, recovery occurs in opposite order

Side Effects: Class I antiarrhythmic, conduction failure, Vfib
B/c LAs are mixed with epinephrine to delay diffusion outside site of injection, can cause vasodilation. At end arteries could cause gangrene
low dose: sedation, high dose: convulsions
allergic dermatitis and asthma

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Types of local anesthetics

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Injection: Bupivacaine, mepivacaine, lidocaine, tetracaine and procaine
Opthalmology: Tetracaine b/c least corneal damage or mydriasis
Ointments
Low Solubility: Benzocaine

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Procaine

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low potency, slow onset, and short duration

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Lidocaine

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3-4x more potent than procaine
more rapid, longer duration

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Mepivacaine

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similar to lidocaine
effective without vasoconstrictor (can be used with CV disease)

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Bupivacaine

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10x more potent than procaine
epidural anesthesia

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Tetracaine

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10x more potent than procaine
Slower onset of action

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Benzocaine

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Topically only