VPT 321: Veterinary Neuropharmacology (2+1)

MECHANISM OF ACTION 

• Local anaesthetics block nerve conduction by decreasing entry of Na⁺ ions during action potential

• As the concentration of LA is increased – rate and rise of spike potential decreases leading to slowing down of conduction
• Local anaesthetic enters the inside of the cell in unionized form and gets ionized (cationic)
• Binds to the receptor on the Na⁺ channel and stabilizes channel in the inactivated state.
• Blockade efficient at a rapidly stimulated nerve rather than a resting nerve
• Higher frequency of stimulation greater is the  blockade
• Small and nonmyelinated fibres more sensitive than myelinated fibres View image...
• Autonomic nerves more susceptible than somatic fibres
• Order of blockade – pain – temperature– touch – deep pressure sense
• Small sensory fibres more vulnerable than motor fibres
• Addition of epinephrine prolongs action by vasoconstriction
• Reduces systemic toxicity of local anaesthetic
• Increases local pain, edema and painful injection
• May cause arrhythmia and hypertension