2005B03 Write brief short notes on the physicochemical properties of lignocaine.

 

Structure

·   Lipophilic modified benzene ring, amide chain, terminal amine N(C2H5)2

·   Achiral

·   Molecular weight 234g/mols

Behaviour

·   Weak base

opKa 7.9

oECF pH: 25% unionised

oICF pH: >90% unionised

·   Lipid solubility 150x procaine

Additives

·   HCl: ↓pH -> ↑ionisation -> ↑solubility

·   Sodium metabisulfite: antioxidant/antibacterial (can cause hypersensitivity)

Formulation

·   Aqueous solution for injection

·   Solution for spray onto upper airway

·   Topical gel

·   With prilocaine as EMLA

 

 

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