Local anesthetics

Question 1

What is the definition of a local anesthetic?

Answer 1

Any substance that produces a reversible nerve blockade.

Question 2

What are the two major types of local anesthetics?

Answer 2

Amides and esters

Question 3

Drugs with two i’s in the name are _____. Drugs with one i are _____.

Answer 3

amides - two i’s

esters - one i

Question 4

Where in the body are esters metabolized? By what enzymes?

Answer 4

In the blood by plasma or pseudocholinesterase

Question 5

What is the half life of an ester LA?

Answer 5

minutes

Question 6

Degradation of ester LA’s forms _____. Is the metabolite toxic? Can people be allergic to this?

Answer 6

PABA is toxic and a possible allergen.

Question 7

Where are amide LAs metabolized? By what enzymes?

Answer 7

In liver by CYP450

Question 8

What is the half life of an amide LA?

Answer 8

Hours

Question 9

Does renal disease affect LA dosing?

Answer 9

Nope

Question 10

Does pregnancy affect LA metabolism?

Answer 10

Yes, metabolism is slowed (half life increases)

Question 11

Are sepsis, malignany, and cardiac ischemia significant clinically in dosing LAs?

Answer 11

Nope

Question 12

What is the mechanism of action of local anethetics?

Answer 12

They bind to receptors inside Na+ channels and decrease the rate of rise of the action potential so the depolarization threshold is not reached.

Question 13

What is the most important factor in onset of action of a LA? Explain.

Answer 13

pKa must be close to physiological pH so that the drug can dissociate from the protonated form to cross the cell membrane, then reassociate with a proton inside the cell to enter the sodium channel and bind the receptor.

Question 14

Are LAs weak acids or weak bases?

Answer 14

weak bases

Question 15

What is the most important factor in the potency of a LA?

Answer 15

Lipid solubility. More lipid solubility = greater potency.

Question 16

What is the most important factor in the duration of action of a LA?

Answer 16

Protein binding. More protein binding = longer duration

Question 17

Name the three major clinical effects of LAs in their correct order.

Answer 17

1. Sympathetic block
2. Sensory block
3. Motor block

Question 18

Which is more easily blocked: myelinated or non-myelinated nerves?

Answer 18

Myelinated

Question 19

What are the signs of systemic LA toxicity in the correct order?

Answer 19

1st - light-headedness and numb tongue and lips
2nd - respiratory arrest
Last - cardiovascular depression

Question 20

How is systemic LA toxicity treated?

Answer 20

Lipid infusion to pull lipid soluble drug out of cells and into the “lipid sink” in the blood.

Question 21

Are pregnant women more susceptible to systemic toxic effects of LAs?

Answer 21

Yeah

Question 22

What is a major side effect of benzocaine and prilocaine (local anesthetics)?

Answer 22

They can oxidize Hb –> metHb

Question 23

True or false: Local anesthetics cause the reversible interruption of afferent and efferent neural conduction.

Answer 23

True