Local Anesthetics

Question 1

What is the definition of a local anesthetic?

Answer 1

It is a drug that blocks nerve conduction and generation of action potentials when applied to any part of the nervous system and on every type of nerve fiber, without loss of consciousness.

Question 2

What is the prototype local anesthetic?

Answer 2

Procaine.

Question 3

What is the most popularly used local anesthetic?

Answer 3

Lidocaine.

Question 4

What was the first highly effective local anesthetic with reversible activity?

Answer 4

Cocaine.

Question 5

What are some desirable characteristics of local anesthetics?

Answer 5

1) Should not be irritating or produce permanent damage.
2) Should not be addictive.
3) Low systemic toxicity.
4) Rapid onset.
5) Duration - sufficiently long to perform a diagnostic or surgical procedure.
6) Should be reversible.

Question 6

What are three chemistry components of local anesthetic compounds?

Answer 6

1) Amine group.
2) Aromatic group.
3) Ester or amide linkage.

Question 7

What does the amine group confer to the compound?

Answer 7

Confers HYDROPHILIC properties.

Question 8

What does the aromatic group confer to the compound?

Answer 8

Confers HYDROPHOBIC (& lipophilic) properties.

Question 9

What does the ester or amide linkage confer to the compound?

Answer 9

Determines route of metabolic degradation and potential allergic reactions.

Question 10

What does the molecular size of the compound influence?

Answer 10

Influences rate of dissociation of local anesthetics from their receptor sites.

Question 11

What are three common LA’s that have ester linkage?

Answer 11

1) Cocaine.
2) Procaine.
3) Tetracaine.

Question 12

What common LA has an amide linkage?

Answer 12

Lidocaine.

Question 13

How is absorption of a local anesthetic agent determined?

Answer 13

Determined by site of injection, dosage, presence of vasoconstricting agent and pharmacological profile of the local anesthetic itself.

Question 14

What is pH critical for in terms of local anesthetics?

Answer 14

pH is critical for local anesthetics effectiveness.

Question 15

What is the makeup of a local anesthetic and how are they marketed?

Answer 15

Local anesthetics are weak bases (only slightly soluble), marketed at HCl salts.

Question 16

Why is cell penetration of a local anesthetic poor in infected and necrotic tissues?

Answer 16

Infected and necrotic tissues have a lower pH, consequently there will be a very low fraction in the unionized form and cell penetration will be poor.

Question 17

What is the pH characteristic of?

Answer 17

The environment.

Question 18

What is the pKa characteristic of?

Answer 18

The drug.

Question 19

Local anesthetics are what _____ (acids or bases)?

Answer 19

Weak bases.

Question 20

What would you dissolve local anesthetics in because they are weak bases?

Answer 20

Acids (commonly HCl).

Question 21

At a low pH, local anesthetics are primarily what? Ionized or unionized?

Answer 21

Ionized.

Question 22

If a local anesthetic is in a low pH and primarily ionized, what will it do physiologically?

Answer 22

Interaction with the receptor rather than facilitate crossing of the membranes.

Question 23

A necrotic tissue is basic or acidic?

Answer 23

Slightly acidic compared to normal.

Question 24

Does it take more or less time for necrotic tissues to be anesthetized?

Answer 24

More time.

Question 25

What can be added to a local anesthetic to help prolong the effect?

Answer 25

Epinephrine or other adrenergenic compounds.

Question 26

What three effects will adding epinephrine to the solution of local anesthetic cause?

Answer 26

1) Prolong drug duration by decreasing blood flow (local vasoconstriction).
2) Decrease systemic toxicity by slowing absorption.
3) Delay healing or cause local tissue necrosis or edema.

Question 27

What is important in assessing the toxicity of local anesthetics?

Answer 27

The rate of metabolism and the metabolic by-products.