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Local Anesthetic Agents Cheat Sheet by

Local Anaest­hes­ia:

- 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.

Clas­sif­ica­tion:

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

Path to receptor site:

Inte­raction with Sodium Channe­ls:

 

Adverse Effects:

CNS
sedation, light headed­ness, visual and auditory distur­bances
 
tongue numbness and metallic taste
 
tonic-­clonic convul­sions (at higher dose)
Card­iot­oxi­city:
Profound effects on conduction and function
 
Heart Block
> Pre-me­dic­ation with Benz­odi­aze­pines can prevent CNS side effects

Clinical Uses:

Surface anesth­esia:
lidocaine, benzoc­aine, tetracaine
Infi­ltr­ation anesth­esia:
most agents, minor surgeries
Nerve block:
most agents, for surgery, dentistry and analgesia.
Spinal anesth­esia:
mainly lidocaine
Local anesthetic agents used with a vaso­con­str­ict­or:
> localised neuronal uptake
> adrenaline can potentiate neurot­oxicity of LA
 

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