Local Anaesthetics Flashcards
What order do LAs block in?
Small myelinated axons
Non-mylenated axons
Large mylenated axons
What is blocked first by LAs?
Nociceptive and sympathetic transmission
What is the progression of LAs?
Pain
Cold
Warmth
Touch
Deep pressure
Motor function
What is a local anaesthetic?
A drug which reversibly prevents transmission of nerve impulses in the region in which it is applied, without affecting consciousness
What is the structure of a local anaesthetic?
Aromatic ring, ester or amide linkage and a tertiary amine
Ester linkage in LAs
More easily broken and not heat stable
Metabolism can result in PABA which can cause allergic reaction
What is a stereoisomer?
Same structural and molecular formula but different spatial orientation around a chiral centre
Why does stereoisomerism matter in LAs?
R & S enantiomers have differing efficacies and SEs
Example of an achiral LA
Lignocaine
What are LAs?
Weak bases used clinically in their salt forms
What defines the % ionisation of a LA in the body?
The pKa of the drug and the pH of the body
Equation for % ionisation of LAs
% ionised = 100/1+ 10^pH-pKa
What does a higher pKa of LA mean?
Less drug is available to cross the lipid membrane to get to target site
