Local Anesthetics

Question 1

MOA of Local Anesthetics

Answer 1

Bind and block Na+ voltages-gated channels to not allow propagation of signal - NON-SELECTIVE
Block channels in the open/inactivated state

Question 2

T/F: The action of Local Anesthetics is terminated by redistribution

Answer 2

True:
Use vasoconstrictors (epinephrine) to decrease distribution away from the site of action

Question 3

Ester LA

Answer 3

Rapidly broken down by plasma pseudocholinesterases

Question 4

Amide LA

Answer 4

Mainly metabolized by the liver

Question 5

T/F: Motor transmission is blocked before pain and sympathetic transmission

Answer 5

False:

Pain and sympathetic transmission are blocked before motor transmission

Question 6

List the order in which fibers are blocked: A-alpha fibers, A-delta fibers, C fibers

Answer 6

A-delta fibers
A-alpha fibers
C fibers

Question 7

T/F: The potency increases by increasing lipid and water solubility

Answer 7

True

Question 8

T/F: The higher the pKa, the more unionized drug enters the axon

Answer 8

False:

The LOWER the pKa, the more unionized drug enters the axon

Question 9

Which LA are part of the Ester subclass?

Answer 9

Procaine
Benzocaine
Proparacaine
Tetracaine
Way to remember: All Esters only have one "i" in their name; All Amides have two "i" in their name

Question 10

Which LA are part of the Amide subclass?

Answer 10

Lidocaine
Bupivicaine
Mepivacaine
Prilocaine
Ropivacaine
Dibucaine
Way to remember: All Esters only have one "i" in their name; All Amides have two "i" in their name

Question 11

Clinical uses of Procaine

Answer 11

DO NOT USE THIS DRUG
Regional anesthesia
Dx lameness in horses
Ventricle arrhythmia (DONT USE WITH EPINEPHRINE)

Question 12

Clinical uses of Benzocaine

Answer 12

Topical absorption in fish only

Question 13

Clinical uses of Proparacaine

Answer 13

Topical corneal and conjunctival manipulation

Question 14

Clinical uses of Tetracaine

Answer 14

Topical corneal and conjunctival manipulation

Euthanasia with Embutramide

Question 15

Clinical uses of Lidocaine

Answer 15

Endotracheal intubation in cat
IM with Oxytetracycline (because it’s painful)
Euthanasia with Embutramide
MOST common LA in vet med

Question 16

Clinical uses of Bupivacaine

Answer 16

Nerve block
Epidural (does not work topically)
Second most widely used LA

Question 17

Clinical uses of Mepivacaine

Answer 17

Nerve block

Dx lameness in horses

Question 18

Clinical uses of Prilocaine

Answer 18

IV regional anesthesia

Question 19

Clinical uses of Ropivacaine

Answer 19

Nerve block

Dx lameness in horses

Question 20

Clinical uses of Dibucaine

Answer 20

Euthanasia with Secobarbital

Question 21

Contraindications for Procaine

Answer 21

DO NOT USE THIS DRUG
Sulfonamide use
Toxic to horses

Question 22

Contraindications for Lidocaine

Answer 22

Do NOT use in food animals

Metabolite is considered carcinogenic

Question 23

Contraindications for Bupivacaine

Answer 23

MOST cardiotoxic

Question 24

Special considerations for Procaine

Answer 24

DO NOT USE THIS DRUG
SLOW ONSET, SHORT DURATION
Rapidly metabolized to PABA
Slows PenG absorption from muscle
CNS stimulation in horses - TOXIC
Horses are the most sensitive species

Question 25

Special considerations for Benzocaine

Answer 25

LOWEST pKa (2.5) - ionized and low solubility

Question 26

Special considerations for Proparacaine

Answer 26

``` RAPID ONSET (30 sec.) and SHORT DURATION (10-20 min) LESS irritating than Tetracycline ```

Question 27

Special considerations for Tetracaine

Answer 27

LONGER duration than Proparacaine | Intrathecal

Question 28

Special considerations for Lidocaine

Answer 28

``` RAPID ONSET (5 min) and MEDIUM DURATION (40-60 min) Used parenterally or topically Max dose = 7mg/kg - sheep most sensitive ```

Question 29

Special considerations for Bupivacaine

Answer 29

``` SLOW ONSET (20 min) and LONGEST DURATION (8 hrs) Max dose = 2mg/kg ```

Question 30

Special considerations for Mepivacaine

Answer 30

LESS irritating than Lidocaine

Question 31

Special considerations for Prilocaine

Answer 31

SIMILAR to Lidocaine but LESS toxic to cardiac muscle | Emla cream - 20-30 min to full effect (dermal analgesia)

Question 32

Special considerations for Ropivacaine

Answer 32

SIMILAR to Bupivacaine but has SHORTER DURATION and LESS toxic

Question 33

Special considerations for Dibucaine

Answer 33

MOST potent and MOST toxic LA

Question 34

T/F: All Esters cause methemoglobinemia

Answer 34

True

Question 35

T/F: All Esters cause histamine release

Answer 35

True: | Histamine release caused by PABA