- Loss of sensation in a limited region of the body
- Localized analgesia
- Drug delivered to target
- aka "regional anesthesia"
Local anaesthetic agents provide complete loss of sensory modalities.
Henderson- Hasselbach Equation:
> Uncharged form is more lipid soluble
> Lower the pKa, the greater the percentage of unchanged weak base at a given pH
> Basic drugs: more will be lipid soluble form at alkaline pH
Pharmacokinetics of Local Agents:
> Exists as weak bases
> pKa of most LA agents ranges 7.5 to 9.0
mainly exist in cationic form at physiologic pH
> Benzocaine (pKa 3.5)
exists mainly in non-ionized form at physiological pH
> Cationic form is most active at receptor site
receptor site at the inner vestibule of the sodium channel
Mechanism of Action:
> Block voltage-gated sodium channels
> During excitation, sodium channels are opened=
- Sodium influx
- Opening of sodium channels result in depolarization
Interaction with Sodium Channels:
sedation, light headedness, visual and auditory disturbances
tongue numbness and metallic taste
tonic-clonic convulsions (at higher dose)
Profound effects on conduction and function
> Pre-medication with Benzodiazepines can prevent CNS side effects
lidocaine, benzocaine, tetracaine
most agents, minor surgeries
most agents, for surgery, dentistry and analgesia.
Local anesthetic agents used with a vasoconstrictor:
> localised neuronal uptake
> adrenaline can potentiate neurotoxicity of LA
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