Local anaesthetics Flashcards
How do local anaesthetics work?
By causing a reversible block of conduction along nerve fibres via blocking voltage gated Na+ channels
How do they bloc Na+ channels?
When the channel is open they block the pore from within as ionised form
Therefore use dependent
Which nerves are affected the most?
Small fibres and myelinated fibres (less areas to block- nodes of ranvier)
Which fibres are affected?
Afferent and efferent fibres, and neuromuscular junctions (droopy face in dentist)
Ideal local anaesthetic?
reversible, non-irritant, short time lag, low system toxicity, readily metabolised once in blood
What makes is have a low duration of action
Water soluble, well perfused site, causes vasodilation, and lack of co-administered adrenaline
How are the drugs metabolised?
Hydrolysis (rapid in plasma for ester bond)
slower in liver for amide bond
Cocaine is used how? Other effects?
Used topically in opthalmology
But inhibits re-uptake of NA (amphetamine like stimulation)
Why is cocaine snorted?
To avoid first pass metabolism
What causes the tissue damage in snorting cocaine?
Local vasoconstriction due to ↓ NA reuptake leads to tissue damage
Name 5 local anaesthetics
Procaine, Lidocaine, Bupivacaine, Prilocaine, Amethocaine
How are they administered?
Surface via ointments, nasal sprays etc
Infiltration via injection
Injections can be given in 3 ways-
Nerve trunk block
Epidural (leaky)
Spinal (can tilt patient)
Side effects of local anaesthetics?
Nausea, vomiting, abdominal trunks
Nervousness, tremors, convulsions,
respiratory depression, cardiovascular collapse
