Local Anesthetics Flashcards
How are local anesthetics typically terminated ?
By redistribution away from site of action (unless vasoconstrictors - adrenaline are applied at the same time).
These are contraindicated where the blood supply to an organ may be compromised by vasoconstriction.
How are esters metabolized?
Plasma cholinesterase
How are amides broken down?
Liver
How is lidocaine broken down ?
Lidocaine is an amide and therefore, completely metabolized by the liver - cannot be given orally.
How are LA eliminated ?
Excreted through the kidneys
What are the signs of LA toxicity
- sedation
- convulsions
- cardiotoxicity
- automaticity depressed
- myocardial toxicity (esp bupivicaine)
Since IV administration causes side effects, care should be taken to ensure that the drugs are NOT injected into a vein.
What is the most commonly used LA?
Lidocaine
What is the advantages of using lidocaine?
- Chemically stable
- Spreads through tissues
- used as 1-2% solution parenterally
- 4% topically
- rapid onset (5 mins) and a medium duration of action (30-40 mins)
What is the advantage of using Prilocaine over Lidocaine ?
Less toxic.
Other properties are similar
What is Prilocaine primarily used for?
Bier’s block (IVRA)
What is the advantage of Mepivicaine over Lidocaine?
It is less irritating.
What is the primary indication of Mepivacaine?
Used in horses for a diagnostic nerve block
Which LA is potent, has a slower onset but longer duration of action?
Bupivacaine
slower onset - 20 mins
Longer action - 8 hours
What is Bupivacaine primarily indicated for?
post op analgesia
Which drug is similar to Bupivacaine, is less toxic but much more expensive ?
Ropivacaine
Which LA is the only ester used clinically and administered in the eye?
Tetracaine
