Local Anesthetics

Question 1

Administration methods of local anesthetics

Answer 1

-topical -local/field -intravenous block -peripheral nerve -plexus (brachial, lumbar) -central neuralgia (epidural, spinal)

Question 2

Which has a longer half life, mepivacaine or lidocaine?

Answer 2

Mepivacaine (> 1 hr)

Question 3

Define frequency-dependent block

Answer 3

Local anesthetics require the Na+ channel to be open in order to block it; thus, the greater the activity of he nerve, the greater the chance it will be blocked

Question 4

What is the duration of a local anesthetic dependent on?

Answer 4

How well it penetrates the axoplasm and reaches the Na+ channel

Question 5

Lidocaine

Answer 5

Classification: local anesthetic & antiarrhythmic

MOI: blocking of Na+ channels

Uses: local and topical anesthetic, occasionally used to treat ventricular arrhythmias

Contraindications: known sensitivity to drug class, Adams stokes syndrome, severe SA, AV, or intraventricular heart block

Adverse effects: dose-related, CNS depression

Administered: IV, SC

Cross BBB? Yes

Elimination: metabolized by liver

Question 6

Define local anesthetic

Answer 6

Drug that produces “reversible loss of sensation in an area of an animal’s body without loss of consciousness or alteration of CNS activity”

Question 7

Mepivacaine

Answer 7

Classification: local anesthetic MOI: blocking of Na+ channels Uses: preferred local anesthetic used in horses: spinal, laryngeal, lower leg & intrathecal use Contraindications: known sensitivity to class of drugs, heart block Adverse effects: dose-related, CNS depression, cardiotoxicity, tissue edema at site of injection Administered: SC Cross BBB? Yes Elimination: metabolized by liver

Question 8

What are the two types of local anesthetics?

Answer 8

Amino amides (most common) Amino esters (degraded by enzymes- plasma esterases)

Question 9

If there is an “i” before the caine, the drug is an amide or ester?

Answer 9

Amide (e.g. Lidocaine, Bupivacaine, Mepivacaine)

Question 10

Why is Bupivacaine not advised to be administered IV?

Answer 10

Due to cardiotoxicity

Question 11

What is the general structure of most anesthetics?

Answer 11

Lipophilic end and hydrophilic end

Question 12

The amount of local anesthetic that reaches the blood depends on which 4 things?

Answer 12

1. The site of injection
2. presence/absence of vasoconstrictors, the physical property of the drug, and the amount injected

Question 13

Methemglobinemia is a rare potential side-effect of what local anesthetic?

Answer 13

Lidocaine

Question 14

What is the effect of protein plasma binding on the effects of a local anesthetic?

Answer 14

If absorbed from the injection site into circulation, the drug must be free and non ionized

Question 15

What is the mechanism of action of anesthetics?

Answer 15

They target sodium channels in excitable cells (Nav1 and Nax) and block conduction of these nerves (block action potential/pain signal)

Question 16

Why are unmyelinated and thinly myelinated axons the major targets of anesthetics?

Answer 16

Because these are the axons that generate/carry pain signals

Question 17

Bupivacaine

Answer 17

Classification: local anesthetic MOI: blocking of Na+ channels Uses: local anesthetic, spinal & intrathecal use Contraindications: known sensitivity to class of drugs, heart block Adverse effects: dose-related, CNS depression, cardiotoxicitiy (> than lidocaine) Administered: SC, intrathecal, spinal Cross BBB? Yes Elimination: metabolized by liver

Question 18

True or False? Cocaine was the first utilized topical anesthetic in human medicine

Answer 18

True

Question 19

What is the name of the local anesthetic restricted to ophthalmic use?

Answer 19

Proparacaine

Question 20

What is the onset of action?

Answer 20

Time the local anesthetic takes a to produce blockade; dependent upon placement of drug, molecule, size, and pKa

Question 21

True or false? In order for local anesthetics to work, the sodium channel must be open

Answer 21

True

Question 22

Describe methemoglobinemia

Answer 22

-iron in hemoglobin is stabilized in ferric (Fe3+) form > O2 is unable to bind, results in hypoxia and death - Lidocaine is an oxidizer -can treat w/ methylene blue

Question 23

Unmyelinated axons are affected more/less quickly than the larger myelinated fibers?

Answer 23

More

Question 24

What is the potency of a local anesthetic related to?

Answer 24

Lipid solubility & pKA > promote penetration of drug to site of action

Question 25

What two systems do local anesthetics have effects on?

Answer 25

CNS (depression) and cardiovascular (decrease in force of contraction)

Question 26

The adverse effects to local anesthetics observed in patients are correlated to what?

Answer 26

The amount/concentration of the dose of local anesthetic given

Question 27

For myelinated nerves, at least ____ nodes of Ranvier must be blocked to produce the effect?

Answer 27

Two