Local Anesthetics Flashcards
goals for local anesthetic use
Minimize local irritation
Minimize systemic toxicity
Rapid onset: high percent needed
Sufficient duration
amide metabolism
in the liver. protein binding
ester metabolism
plasma pseudocholinesterase
Mechanism of action for LA
Identical to one of the Anti convuls/epilep drug mechanisms. Block Na channels from the inside of channel. Stabilize inactived state.
Quartenary lidocane and nerve effects
ineffective from outside. must be injected directly into nerve.
Effect of block on nerve myelination and diameter.
Small and unmyelinated are most sensitive to effect.
Order of sensory/motor nerve block sequence
pain > cold > touch > deep pressure > motor function
7 factors influencing effectiveness of LA
Fiber diameter, firing rate (action potential duration - use dependent block), position of fiber in nerve bundle, local blood flow, drug size and hydrophobicity, liver function (amines). Tissue pH - consequence of inflammation
2 Considerations when using epinepherine in local
Location of block (distal portion also being blocked). Slows local blood flow.
PkA of lidocaine
7.9
At more acidic pH (lidocaine)
less drug is uncharged and less drug crosses nerve membranes, and therefore less nerve block.
Toxicity of LA on CNS
Drowsiness, seizures (excitation), followed by general depression, coma
Toxicity of LA on Cardiac
Depressed pacemaker activity, decreased conduction, arrhythmias, potentiated by hperkalemia, amides synergize with anti-arrhythmic drugs to induce arrythmias
Toxicity of LA on vessels
vasodilation leading to hypotension (except cocaine - HTN caused by block of NE reuptake)
LA common allergies
esters: PABA derivatives. Amides: Preservatives
