Local Anesthetics

Question 1

Properties of an ideal local anesthetics?

Answer 1

short onset, long action
remain at site of injection
act predictably/reversibly w/o tissue damage
possess lg safety margin

Question 2

What are the three components of a local anesthetic?

Answer 2

Aromatic ring
Intermediate linkage (ester or amide)
terminal amine

Question 3

What does the aromatic ring portion of local anesthetic determine?

Answer 3

lipophilicity which determines potency & duration of action

local anesthetics w/ high protein binding have longer duration of action

Question 4

What are esters and amides metabolized by respectively?

Answer 4

Plasma esterases

Hepatic Amidases

Question 5

Characteristics of amino esters?

Answer 5

shorter duration of action and increased risk of allergy in comparison to amino amides

Question 6

Name four amino esters.

Answer 6

Cocaine, procaine, benzocaine, tetracaine

Question 7

Name six amino amides.

Answer 7

Lidocaine, Mepivicaine, Bupivicaine, Prilocaine, Ropivicaine, Dibucaine

Question 8

Where are amino amides metabolized?

Answer 8

Liver, increased toxicity risk w/ decreased liver fx

Question 9

How are amino amides cleared?

Answer 9

kidneys

Question 10

What does the terminal amine portion of local anesthetics determine?

Answer 10

hydrophilicity which correlates with onset of action

Question 11

What determines the onset of action?

Answer 11

pKa of the anesthetic and local pH

Question 12

When can a local anesthetic diffuse across a cell membrane?

Answer 12

When the terminal amine is unionized

Question 13

When is a local anesthetic active?

Answer 13

When the terminal amine is ionized (undiffusable)

Question 14

What is the pKa?

Answer 14

Is the pH at which the amount of ionized and unionized drug is equal.

Question 15

What effect does an acidic local environment have on a local anesthetic?

Answer 15

Favors the ionized form and prolongs onset of action

Question 16

What effect does mixing a local anesthetic with sodium bicarbonate have?

Answer 16

Favors the unionized diffusible state and speeds up onset.

Question 17

MOA of local anesthetics?

Answer 17

Blocks intracellular portion of inactivated voltage gated Na+ channels

Question 18

Name three factors that effect the nerve fiber blockade?

Answer 18

size of fiber- smaller, quicker
degree of myelination - more myelinated, quicker
firing frequency- the higher the firing frequency the greater the # of Na+ channels and easier to block

Question 19

A higher pKa leads to more ionized or unionized form of local anesthetic?

Answer 19

More ionized form, less unionized (longer time to penetrate membrane)

Question 20

What three things effect local anesthetic absorption?

Answer 20

Site of injection (highly vasc absorbs more than less vasc)
presence of vasoconstrictors (decreases absorption)
Degree of tissue binding (higher, less absorbed)

Question 21

How does systemic toxicity progress?

Answer 21

Begins as CNS excitation (decreased inhibition, sensory disturbances, tremor, restlessness)

then CNS depression (lethargy, hypotension, seizures)

finally Cardiovascular problems (reduced conductivity, contractility, and excitability)

Question 22

What two drugs are at risk of causing methemoglobinemia in large doses?

Answer 22

Benzocaine and prilocaine

Question 23

Is it normal or unusual for a pt to have allergies to local anesthetics?

Answer 23

Unusual