Local Anesthetics

Question 1

Effect of Na channel blockade on Na channels

Answer 1

Slow the upstroke rate + amplitude

Can get rid of AP alltogether

Question 2

How much Na channel blockage is required for effect

Answer 2

50-70%

Need to reduce Na by 2x as much as K

Question 3

Four main factors effecting the pharmacological action of Na channel blockers

Answer 3

1. Frequency of Transmission (hits high frequency)
2. Size/Class of Peripheral Axons
3. pH (less effective in infected acidic)
4. Vascularity of Target Tissues

Question 4

How size/class of peripheral axons influences effects of Na channel blockers

Answer 4

Small fibers are blocked better
Myelinated are blocked better
Sensory are selectively blocked
C, B > Adelta > Agmma, beta > Aalpha

Question 5

Explain frequency-dependent block

Answer 5

Many drugs (such as lidocaine) bind well to the open/inactivated state. When firing is slow, this can completely dissociate between stimulations. When firing rapidly, there isn’t enough time to unblock the channels before the next spike, allowing build up.

Question 6

Explain voltage-dependent block

Answer 6

Drugs may block nerves with depolarized membranes best because normally (in hyperpolarized), lidocaine is unbound between spikes. If deporlarized, a high percentage can remain blocked, suppressing activity.

Question 7

Order of loss of nerve function ina block

Answer 7

Pain
Temp
Touch
Deep Pressure

Question 8

Why combine alpha agonists with local anesthetics?

Answer 8

Slows local bloodflow to prolong block

do NOT do in poorly vascularized regions (finger, ear, dick)

Question 9

pH profile of local anesthetics?

Answer 9

pKa 8-9

Weak base

Question 10

Significance of pKA in LAs?

Answer 10

pKA is the pH at which ionized and non-ionized forms equilibrate. closer to physiological pH will cause there to be increased non-ionized form, which can cross membranes, making onset faster. Ionized is still needed, because that binds the channel.

Question 11

The listed local anesthetic prototypes

Answer 11

Cocaine
Procaine
Lidocaine

Question 12

Two primary classes of local anesthetics

Answer 12

Amides and Esters

Question 13

Important Amide local anesthetics

Answer 13

Bupivacaine (high potency)
Lidocaine
Prilocaine
Ropivacaine

Question 14

Important Ester local anesthetics

Answer 14

Benzocaine
Cocaine
Procaine (Low Potency)
Tetracaine (High Potency)

Question 15

Amide local anesthetic details

Answer 15

Fast Onset. Med/Long Duration

Hydrolysis by CYPs

Question 16

Ester local anesthetic details

Answer 16

Variable onset, short/long duration

Hydrolysis by esterases

Question 17

Potency and duration correlate well with a drug’s…

Answer 17

lipid solubility

Question 18

Cardiovascular toxicities of local anesthetics

Answer 18

Arrythmias, Depressed Cardiac AP

Cocaine also causes vasoconstriction/HTN

Question 19

Neuro toxicities of local anesthetics

Answer 19

CNS stimulaton (treat w/ benzos)
Respiratory Depression/Death
Addiction

Question 20

Which local anesthetics are topical?

Answer 20

Benzocaine
Lidocaine
Tetracaine

Question 21

Which LAs are local injection

Answer 21

Lidocaine
Procaine
Bupivacaine

Question 22

Which LAs are nerve block

Answer 22

Lidocaine

Mepivacaine

Question 23

Which LAs are spinal

Answer 23

Bupivacaine

Tetracaine

Question 24

Which local anesthetic is used for eipdural

Answer 24

Bupivacaine

Question 25

Which LA is used for Caudal

Answer 25

Lidocaine

Bupivacaine