Local Anesthetics Flashcards
Esters
- cause more hypersensitivity reactions
- only 1 letter “i”
Ester durations and potency
Short: Procaine (1)
Long: Tetracaine (16)
Topical/Surface: Benzocaine, cocaine (2)
Amides
-2 letter “i”s
Amides duration and potency
medium: lidocaine (4), mepivacaine (2)
Long: bupivacaine (16), ropivacaine (16)
Esters: Onset and duration
- Procaine:
onset: 2-5min
duration: 25 min to 1 hour - Tetracaine
onset: <15 min
duration: 2-3 hours
Amides: onset and duration
- Mepivacaine
onset: 3-5 min
duration: ~1hr - Bupivacaine
onset: 5 min
duration: 2-4 hrs - Lidocaine
onset: <2min
duration: 30min - 1hr - Ropivacaine
onset: 10-30min
duration: ~30min
Local anesthesia MOA
block voltage-dependent sodium channels of excitable membrane from sending sensory info to the CNS
Which form of local anesthetic is better/faster at crossing the lipid membrane to reach the cytoplasm receptor site?
Non-ionized form
Which form of local anesthetic is the more effective blocking entity once inside the axon?
Ionized form
What effect does sodim bicarbonate have when added to a local anesthetic?
- Accelerates the onset of action
2. Decreases burning sensation
What effect does adding epinephrine (alpha agonist sympathomimetic vasoconstrictor) to a local anesthetic?
prolongs duration
long acting don’t need this - bupivicaine, ropivicaine, tetracaine and neither do topical local anesthetics
What is the difference in esters and amides when it comes to metabolism?
Esters - metabolized in the blood by plasma cholinesterases (very rapid)
Amides -metabolized by liver (so, higher risk of liver toxicity with liver dysfunction)
What type of fiber would be most easily blocked?
a small myelinated fiber
What type of fiber would be most difficult to block?
a large unmyelinated fiber
Which type of fiber is hardest to block?
Type A - Alpha (proprioception, motor)
Which type of fiber is easiest to block?
Types B, C and Type A - delta (pain, temperature)
Which would be blocked first a medium myelinated fiber or a small unmyelinated fiber?
the myelinated fiber
A-alpha fiber
- muscle proprioception
- Largest fiber type
- myelinated
A-beta fiber
- Second largest fiber
- Touch
- myelinated
A-delta fiber
- 3rd largest fiber
- pain and temperature
- myelinated
C-nerve fiber
- Not myelinated
- pain, temperature, itch
- Small fiber
Sequence of nerves to be blocked
- Sympathetic
- Temperature
- Pain
- Light touch
- Motor
Epidural block
-local anesthetic extradurally
Caudal block
-epidural block in the caudal canal via the sacral hiatus
Spinal block
injection into cerebrospinal fluid in the subarachnoid space
Why is bupivacaine banned by the FDA in obstetrics for epidural anesthesia?
cardiotoxicity
How can you tell local anesthetics with and without epinephrine by the label on the bottle?
red label if it contains epi
Amides local anesthetics
Pharmacokinetics: hepatic metabolism
- bupivacaine is most likely to cause heart problems
- CNS effects (light headed, sedation, restlessness, nystagmus, tonic-clonic convulsions
Ester local anesthetics
Pharmacokinetics: rapid metabolism by plasma esterases
- Metabolites can cause antibody formation
ex. Benzocaine, cocaine, procaine, tetracaine
Prilocaine: ADE
can convert hemoglobin to methemoglobin
What medication is given to someone having a convulsion due to anesthetic toxicity?
Diazepam IV (Valium)
