Local Anesthetics Flashcards
Define local anesthetics
Produce loss of sensation in limited region by blocking impulse conduction in sensory fibers
What drugs make up LAs?
“-caine” drugs
Amides
+Bupivacaine
+Lidocaine
+Prilocaine
Esters
+benzocaine
+Tetracaine
(Cocaine)
Describe MOA of LAs
Block voltage gated sodium channels
Local anesthetics are weak bases… their base form can pass membrane
Once inside the cell, the more acidic environment protonates the base which will diffuse into the open (activated) channel
This holds the Na channel in an inactivated state
Compare conduction velocity and sensitivity to block in large and small fibers
Conduction faster in axons with large diameters
Smaller diameters/unmyelinated fibers more sensitive to block
What other factors influence action of local anesthetics ?
Axon activation (When membranes are depolarized, the block of Na channels mean theres more opportunity for LAs to enter channel)
pH
Differentiate between spinal and epidural anesthesia modes of administration
Spinal = inject to CSF
Epidural = inject to epidural space
How is LA action terminated?
LA gets into systemic circulation and is metabolized
Esters = metabolized in plasma
Amides = metabolized in liver
Differentiate durations of action of esters vs. amides
Esters = short duration
Amides = long duration
Hepatic disease can inc. duration
How do vasoconstrictors affect LA duration of action?
Vasoconstrictors like EPI can prolong duration
What are AEs associated with LAs?
CNS effects: tongue tingling/numbness = light-headed = unconsciousness = seizure
CV effects \+bradycardia \+arrhythmias \+myocardial arrest \+shock \+hypotension
Allergic reactions
What are examples of amide LAs?
Bupivacaine
Lidocaine
Prilocaine
What are examples of ester LAs?
Tetracaine
Benzocaine
What is another AE most commonly seen with ester LAs?
Hypersensitivity
Since they get metabolized to PABA
What is an AE seen most commonly with Prilocaine (amide)
Methemoglobnemia
Iron in Hb oxidized, resulting in dec. oxygen transport
