Exam #01b - Local Anesthetics

Question 1

At what location on the nerve pathway do LA’s work?

Answer 1

at the primary afferent neuron

Question 2

LA would penetrate all of the following except:

A) smaller axons before larger axons
B) myelinated axons before nonmyelinated axons
C) outer nerves before inner nerves in large mixed nerves
D) rapidly-firing axons before resting axons
E) axons far from the site of injection before axons at the site of injection?

Answer 2

E

Question 3

The unionized LA drug is able to penetrate the cell membrane. However, the ionized LA drug is the only way it has activity. Why is LA drug ionized inside the neuron cell?

Answer 3

There is a lower pH inside the neuron and therefore the LA drug gets ionized

Question 4

All of the following regarding LA’s is true except:

A) Most LA are esters
B) Most LA are amides
C) Most LA are weak bases
D) LA are partly lipid soluble, partly water-soluble
E) all the above are true

Answer 4

E

Question 5

The effectiveness of a LA is a function of what?

Answer 5

pH

Question 6

Why would more LA be required for same effectiveness when injecting into site of inflammation?

Answer 6

Site of inflammation/infection is more acidic with a lower pH. This shifts the equilibrium towards formation of ionized LA drug which results in less penetration, which is why you’d need to administer more LA for the same effect

Question 7

List the Ester LA’s in order of shortest duration to longest (3)?

Answer 7

1. Procaine
2. Cocaine
3. Tetracaine

Question 8

List the Amide LA’s in order of shortest duration to longest (2)?

Answer 8

1. Lidocaine

2. Bupivacaine

Question 9

What (3) criteria is the clinical selection of LA’s based on?

Answer 9

1. DOA
2. Metabolism
3. Elimination

Question 10

What enzyme metabolizes ester LA’s?

Answer 10

plasma cholinesterase (LA’s are not penetrating synapse so AChE is NOT metabolizing ester LA’s

Question 11

What enzyme metabolizes amide LA’s?

Answer 11

liver microsomal enzymes (CYP450) - potential D/D interactions

Question 12

Would liver disease increase or decrease the T1/2 of ester LA’s?

Answer 12

Neither, since ester LA’s are metabolized by plasma cholinesterases. Liver disease would INCREASE T1/2 of amide LA’s since amide LA’s are metabolized by CYP enzymes

Question 13

Which LA type would be a better choice for a patient with liver disease?

Answer 13

ester type LA

Question 14

What effect on T1/2 of amide LA’s would decreased hepatic blood flow cause?

Answer 14

T1/2 would increase

Question 15

How are LA’s primarily excreted?

Answer 15

urine

Question 16

How can you reduce respiratory depression caused by LA’s in brain stem when injecting into spinal cord?

Answer 16

Inject low on the spinal cord. There isn’t much fluid movement in the CSF so not much drug would reach the brain stem

Question 17

Name (8) adverse effects seen with CNS toxicity caused by LA’s (being absorbed systemically aka into blood stream)?

Answer 17

1. light-headedness
2. sedation
3. restlessness
4. nystagmus
5. convulsions
6. coma
7. respiratory depression
8. death

Question 18

How are LA usually dispensed?

Answer 18

as an acidic salt solution (highly water soluble and stable)

Question 19

How do LA slow the propagation of nerve impulses?

Answer 19

By reducing the rate of rise of the AP and the rate of repolarization

Question 20

This term is defined as the exposure time required by an anesthetic in order for it to exert its action?

Answer 20

Critical length

Question 21

What critical length would smaller nerve fibers have?

Answer 21

Proportionally smaller critical length

Question 22

This condition is a late effect that can occur as the result of myocardial depression and peripheral arterial vasodilation?

Answer 22

hypotension