Local Anesthetics

Question 0

Amino Amide anesthetics

Answer 0

Lidocaine, prilocaine, meprivacaine, bupivacaine. (2 I in name)

Question 1

Amino esters

Answer 1

Benzocaine, Cocaine, tetracaine, procaine. (1 I in name)

Question 2

Local anesthetics are weak ________.

1) Are usually made available clinically as ________ to increase solubility and stability.
2) In the body they exist as either uncharged ______ or _______ species.

Answer 2

Bases (pKa- 7.8 to 9.1)

1) Salts
2) Base, cation

Question 3

At physiological pH, local anesthetics will be (positively/negatively) charged?

Answer 3

Positively (cationic form)

Question 4

T/F: The higher the pKa, the greater the percentage of uncharged species at a given pH.

Answer 4

False: The lower the pKa

Question 5

What local anesthetic exists solely as a nonionized base under normal physiologic conditions

Answer 5

Benzocaine, which has a pKa around 3.5

Question 6

MOA for local anesthetics

Answer 6

• Block Na+ channels along axons
• They do so ONLY WHEN CHANNEL IS OPEN.
• Voltage and time dependent manner
• Block is from the INSIDE OF THE CELL.
• Without loss of consciousness
• Reversible manner

Question 7

1) The IONIZED/ NON-IONIZED form of local anesthetics is the portion that is capable of diffusing across nerve membranes.
2) The CATIONIC/ANIONIC form is capable of blocking the receptor.

Answer 7

1) Non-ionized

2) Cationic

Question 8

When progressively increasing concentrations of a local anesthetic are applied to a nerve fiber, what happens?

Answer 8

• The threshold for excitation increases.
• Impulse conduction slows.
• The rate of rise of the action potential declines, action potential amplitude decreases.
• The ability to generate an AP is completely abolished.

Question 9

Local anesthetics are more efficacious on nerves that are rapidly firing or chronically depolarized. What fibers are blocked first? Followed by what fibers?

Answer 9

• Smaller C and B fibers are blocked first.(Pain)
• Followed by a small type A-delta and A-gamma fibers (Pain/temp, muscle spindles)
• A-alpha fibers are blocked last (proprioception, motor)

Question 10

With recovery from a local anesthetic, what sensation returns last?

Answer 10

Pain

Question 11

Potency and duration of action for Ester Local anesthetics

Answer 11

cocaine: P-2 DOA medium
Procaine: P-1 DOA Short
Tetracaine: P-16 DOA Long
Benzocaine: Surface use only

Question 12

Potency and Duration of action for Amide Local anesthetics

Answer 12

Lidocaine: P-4 DOA Medium
Mepivacaine: P-2 DOA Medium
Bupivacaine: P-16 DOA long

Question 13

What is used with local anesthetics to reduce the rate of systemic absorption and thus diminishing peak serum levels?

Answer 13

Vasoconstrictors- EPINEPHRINE

Question 14

Know where you are blocking the pain:

1) Infiltration
2) Infiltration (surround)
3) Infiltration (peripheral)
4) Infiltration (spinal)

Answer 14

1) At point of interest
2) Surround wound
3) In between spinal cord and region of interest.
4) Spinal, epidural, or caudal nerve block.
* Can also have topical

Question 15

What factors influence clearance of local anesthetics?

Answer 15

1) Age
2) Liver fxn
3) Cardiovascular status
4) Type of local anesthetic (Esters hydrolyzed faster then amino amide type)

Question 16

Where and how are Ester linked local anesthetics metabolized?

Answer 16

Metabolized in plasma by plasma cholinesterase

Question 17

Where and how are Amide-linked local anesthetics metabolized?

Answer 17

Metabolized in the liver by Cytochrome p450 enzymes

Question 18

For local anesthetics, whats serves to eliminate or terminate their effect?

Answer 18

Systemic absorption, distribution, and elimination.
*Thus classic pharmacokinetics plays a lesser role than systemic therapeutics, yet are important to anesthetics duration and critical for development of adverse reactions.

Question 19

What would cause systemic toxicity with a local anesthetic?

Answer 19

Inadvertent intravascular injection or absorption of anesthetic from the site of administration.

Question 20

What would cause neurotoxicity with local anesthetics?

Answer 20

Resulting from local effects produced by direct contact with neural elements

Question 21

Systemic toxicity of local anesthetics due to degradation causing hypersensitivity due to formation of what compounds? What does this cause?

Answer 21

1) Benzoic acid, Para-aminobenzoic acid, and derivatives of para-aminobenzoic acid.
2) Causes allergic dermatitis, asthma, fatal anaphylactic reaction.

Question 22

CNS effects of local anesthetics?

Answer 22

1) Early symptom is circumoral and tongue numbness and a metallic taste.
2) High concentrations can cause nystagmus and muscular twitching, followed by clonic convulsions.
- Others: Sedation, light-headedness, visual and auditory disturbances.

Question 23

What is the most feared complication associated with local anesthetic administration?

Answer 23

Cardiovascular effects on cardiac conduction and function.

• Low dose= vasoconstriction and HTN
• High dose= Neg. inotropic effect

Question 24

What symptoms associated with local anesthetics are very rare but devastating neural complications that can occur with spinal and epidural administration causing severe pain?

Answer 24

Transient neurologic symptoms. Reported with lidocaine, procaine, and mepivacaine.

Question 25

What can be administered systemically to treat chronic pain?

Answer 25

systemic local anesthetics