Local Anesthetic Flashcards
MOA of LA
- stop axonal conduction by blocking Na channels
- prevent entry of Na+
- slow down/ inhibit conduction
extracellular pH > intracellular pH
outside the cell, LA is deprotonated, exist in the form of B, can pass through membrane channel to block Na channels from cytoplasmic side of membrane
inside the cell, LA is protonated to exist in the form of B-H, harder for B-H to diffuse out of the cell
What does it mean for a channel to be inactivated?
channel open, gating mechanism closed
LA have higher aiffinity for inactivated channels over resting channels
factors affecting MOA
- lipid solubility: higher, potency higher
- greater effects on smaller nerve: high frequency of a.p, myelinated axons, circumferential nerve
- pH: higher pH, increased LA activity
Name some LA esters
- procaine (short doa)
- tetracaine (long doa)
- cocaine (good penetration, used for ENT)
When to use LA esters over LA amides?
in patients with liver dysfunction
esters are metabolised by esterases
those with liver dysfunction should use LA esters NOT amides
When to use LA amides over LA esters?
when patient is prone to allergic reaction
- esters: prone to allergic rxn as they are metabolised into BPA that can cause allergic rxn
- amides: do not cause allergy rxn
Name some LA amides
- lidocaine (medium doa)
- mepivacaine (medium doa)
- bupivacaine (long doa)
What are LA amides used for?
- epidural
- dental anes (combine with epinephrine)
Adverse effects of LA
- systemic toxicity: large dose
- use epinephrine to prevent LA systemic distribution by vasoconstriction of blood vessels, decrease in blood flow - cardiotoxicity: bupivacaine
- hypertension: cocaine blocks NA upretake, increase in NA, increase in vasoconstriction
- allergy reactions from LA esters: hyrdolysed to p-aminobenzoic acid derivatives (BPA)
