Local anesthetics

Question 1

How can you tell the difference between Esters and Amides

Answer 1

Esters: only 1 “I”
Amides: two “I”’s

Question 2

What are the esters

Answer 2

Short: Procaine
Long: Tetracaine
Surface action: Benzocaine, Cocaine

Question 3

What are the amides

Answer 3

Medium: Lidocaine, Mepivacaine
Long: Bupivacaine, Ropivacaine

Question 4

What local anesthetics have the highest potency

Answer 4

Tetracaine: 16

Bupivacaine, Ropivacaine: 16

Question 5

What is the onset time of certain local anesthetics

Answer 5

Lidocaine, Prilocaine: <2 
Procaine: 2-5
Mepivacaine: 3-5 
Ropivacaine: 10-30
Tetracaine: <15

Question 6

How do local anesthetics work (generally)

Answer 6

-Sensory transmission from a local area of the body to the CNS is blocked= loss of sensation

Question 7

What is the chemical MOA of local anesthetics

Answer 7

Block voltage dependent sodium channels
reduce influx of sodium ions
prevent depolarization of membrane
block conduction of action potential

Question 8

What are the roles of non-ionized and ionized drugs

Answer 8

Non-ion: help reach the receptor site

Ionized: cause the effect

Question 9

Onset of local anesthetic action can be accelerated by

Answer 9

sodium bicarbonate, to enhance IC access of weakly basic compounds

Question 10

What can help prolong the duration of the local anesthetic

Answer 10

Epinephrine (alpha agonist), a vasoconstrictor
Less blood flow= drug stays around longer
*Longer acting agents usually don’t need epi

Question 11

How are Esters metabolized

Answer 11

Metabolized by plasma cholinesterases AKA very rapid

Question 12

How are Amides metabolized

Answer 12

by the liver

higher risk of toxicity with liver dysfunction

Question 13

What fibers are blocked by local anesthetics

Answer 13

Small fibers: more easily blocked than large
Myelinated fibers: more easily blocked than unmyelinated
Fibers in periphery: blocked quicker than fibers in the core of a thick nerve bundle

Question 14

What are the types of pain fibers

Answer 14

A: Alpha, Beta, Gamma, Delta (heavy myelination)
B: preganglionic autonomic (light myelination)
C: dorsal root (pain) (unmyelinated)

Question 15

What do Type A fibers do

Answer 15

Alpha: proprioception, motor
Beta: touch, pressure
Gamma: muscle spindles
Delta: pain, temp

Question 16

The difference in type A and C nerves is

Answer 16

A: sharp pain
C: dull pain

Question 17

Local anesthetics can block

Answer 17

all nerve types!

actions are not limited to the desired loss of sensation from sites of noxious stimuli

Question 18

Central neural techniques (epidural) cause

Answer 18

impaired respiratory activity if motor paralysis is blocked

Hypotension if autonomic nerves are blocked

Question 19

When is motor paralysis desired

Answer 19

during surgery!

Question 20

How can motor paralysis lead to undesirable effects

Answer 20

Epidural during labor: may limit ability to “bear down” and push baby out
Post-op analgesia: mess with ability to ambulate without assistance, interfere with bladder function (urine retention)

Question 21

What is the order of components blocked

Answer 21

Sympathetic transmission 
Temperature 
Pain 
Light touch 
Motor block 
(surgical anesthesia may require loss of touch, not just ablation of pain)

Question 22

Added vasoconstrictors (epi) can also help

Answer 22

• extend duration of post-op pain control, and lower need for total anesthetic
• Decrease risk of toxic effects by lowering peak blood levels of anesthetics

Question 23

When incorporated into spinal anesthetics, Epi

Answer 23

• contributes to prolongation of local anesthetic effect 2/2 vasoconstrictor properties
• Exerts direct analgesic effect mediated by post-synaptic a2 adrenoreceptors in spinal cord

Question 24

What are the types of spinal anesthetics

Answer 24

Epidural: injected extradurally
Caudal block: type of epidural w/ injection into caudal canal
Perineural blocks: injection around peripheral nerves
Spinal block: injection into CSF

Question 25

FDA banned the use of this in labor

Answer 25

0.75% Bupivacaine, 2/2 cardiotoxicity

can be reversed w/ Lipid resuscitation

Question 26

Clinical uses of local anesthetics include

Answer 26

minor surgical procedures
spinal anesthesia
autonomic blockade in ischemic conditions
slow epidural infusion at low concentrations (post-op anesthesia)
IV to reduce pain perioperatively
Oral/parenteral in neuropathic pain

Question 27

On a bottle, Epinephrine is…

Answer 27

RED!!

Question 28

Toxicities of Amides include

Answer 28

CNS excitation, seizures 
Vasodilation, hypotension, heart block
arrhythmias (bupivacaine) 
light headed, restless, nystagmus
*Amides rarely used IV, mostly topical*

Question 29

Toxicities of Esters include

Answer 29

Cocaine vasoconstricts

cocaine abuse= HTN, seizure, cardiac arrhythmia

Question 30

How is cocaine different than other esters

Answer 30

it has intrinsic sympathomimetic actions!

Question 31

What is the avg half life of lidocaine

Answer 31

1.6 hours in normal patients
6+ hours in those with severe liver disease
Longer in those with reduced hepatic blood flow, or if anesthetized with volatile agents that reduce blood flow
Also longer in those with CHF (impaired hepatic blood flow)

Question 32

If you cant take an ester or amide, you may use

Answer 32

Benadryl!!

Question 33

How do you treat toxicity

Answer 33

No antidotes; can manage convulsions with Diazepam*

Question 34

What is EMLA cream

Answer 34

(Eutectic Micture of Local Anesthetics)
2.5% Lidocaine and 2.5% Prilocaine
Allows penetration of keratinized skin= local numbness
Can be used in peds prior to venipuncture (IV or cath placement)