Exam 11: Local Anesthetics Flashcards
Which part of local anesthetics’ structure is important for their entry into the axon?
Lipophilic domain
Which part of local anesthetics’ structure is important for their action at Na+ channels?
Hydrophilic domain
What are the two types of local anesthetics?
Amides (lidocaine)
Esters (procaine)
How are Amide local anesthetics metabolized?
Liver (microsomal enzymes)
How are Ester local anesthetics metabolized?
Plasma cholinesterase
How do the half-lives of Amides compare to Esters?
Amides have longer half-lives because they’re metabolized by liver enzymes as opposed to Esters, which are metabolize by cholinesterase in the plasma
Which chemical form of local anesthetics enters the cell?
Unprotonated (LA)
Which chemical form of local anesthetics is “active” in inhibiting the Na_ channels?
Protonated (LAH+)
Intracellular pH is lower than extracellular
What is the order of neuron sensitivity to nerve block?
Most to least sensitive: C (pain) B (autonomics) A' (pain/temp) A (motor) A+ (motor)
How can you numb an entire limb?
Intravenous regional anesthesia
Put a tourniquet on and inject LA IV
Only useful up to 2 hours
Spinal vs Epidural: Which needs more LA
Epidural
Spinal vs Epidural: Which is more intense of a block?
Spinal
3 Advantages of Epidural over spinal anesthesia
- Not limited to below L2
- No dural puncture = no post-dural puncture headache
- You can leave a catheter in for long-term pain reduction and fine tune the dosage from there
Purpose of giving Epinephrine injection with local anesthetics
Causes vasoconstriction and decreasing absorption
Prolongs duration of effect and reduces the amount of LA needed
2 cautions with epinephrine injection
- Can cause vasodilation at skeletal muscle beds, increasing toxicity
- Dont use it at peripheral sites (nose, fingers, scrotum, ears)
Where can local anesthetics distribute?
Everywhere (cross BBB)
Amides are taken up in fat, brain, kidney, liver, muscle, gut.
Esters are metabolized too fast to be redistributed
What does CSF lack?
Cholinesterase
Local anesthetic side effects at low doses
Sleepiness, dizziness, restlessness
Lidocaine can cause euphoria
Local anesthetic side effects at high doses
Nystagmus, shivering, CNS depression, respiratory failure, convulsions
Treatment for local anesthetic toxicity
Benzos and barbiturates
Only local anesthetic with intrinsic vasoconstrictive properties
Cocaine
the rest are vasodilators
Which local anesthetic is the most cardiotoxic?
Bupivacaine
Which 2 local anesthetics can cause methemoglobinemia?
Prilocaine
Benzocaine
2 Amide Local Anesthetics
Lidocaine
Bupivacaine
Ropivacaine
Articaine
2 Ester Local anesthetics
Benzocaine
Cocaine
What is the most widely used Local Anesthetic today?
Lidocaine
Lidocaine
Amide Local anesthetic
Widely used (including spinals, epidurals, IV)
Excellent diffusions and penetration
Bupivacaine
Amide Local Anesthetic
Long Duration of Action!!!
Not recommended for IV injection due to cardiotoxicity
Caution with Bupivicaine
Dont inject IV
Cardiotoxic
Ropivacaine
New Amide local anesthetic
Useful for procedures where you don’t want motor block (labor anesthesia) because it’s less lipophilic than bupivacaine
Reduced CNS/Cardio toxicity
Pure enantiomer
Articaine
Amide Local Anesthetic
Safer than prilocaine because it metabolized by plasma carboxyesterase (less metabolized in liver)
Benzocaine
Ester local anesthetic
Used topically (skin/mucus membranes)
FDA warning for use in children due to methemoglobinemia
Cocaine!!!
Topical use only
Only Local anesthetic with inherent vasoconstrictive action
No need to co-administer with epi, this could increase toxicity
