Local Anesthetics

Question 1

Analgesics

Answer 1

Specific inhibitors of pain pathways

Question 2

Anesthestics

Answer 2

Non-specific inhibitors of peripheral sensory including pain, motor, and autonomic pathways

Question 3

Local anesthetics

Answer 3

Inhibit conduction of action potentials in all afferent and efferent nerve fibers

Question 4

Local anesthetics- pharmacology

Answer 4

Hydrophobic, weak bases either ester or amide linked

Question 5

Local anesthetics- kinetics

Answer 5

Diffuse to site of action after administration also taken up into systemic circulation.

Question 6

Local anesthetics-distribution

Answer 6

In the blood bind to alpha-1-acid glycoprotein and albumin. Hydrophobic agent has greater binding affinity (bound drug is no longer effective)
Less hydrophobic has greater plasma concentration and vice versa.

Question 7

Ester linked metabolism/elimination

Answer 7

Procaine, tertracaine, and cocaine
Metabolized locally by tissue and plasma esterases (psuedocholinesterase_.
Short DOA and minute metabolism
Eliminated via the kidneys

Question 8

Amide linked metabolism/elimination

Answer 8

Lidocaine, prilocaine, bupivicaine, articaine
Primarily P450 in the liver, although in the lungs as well
Metabolites eliminated via kidney
Longer DOA

Question 9

Tonic inhibiton

Answer 9

Occurs when the time b/w action potentials is long compared to the time of dissociation of the local anesthetic from the Na channel.

Question 10

Phase inhibition

Answer 10

Not enough time b/w action potentials. Action potential conduction increasingly inhibited at higher frequencies of impulses.

Question 11

Procaine

Answer 11

Ester based
Short-acting low hydrophobicity, low potency
Rapidly metabolized in plasma by cholineresterases
Sulfa drugs decrease effectiveness

Question 12

Tetracaine

Answer 12

Ester based
Long-acting, highly potent due to high hydrophobicity
Metabolized by cholinesterase in plasma but slower effect than with procaine as released gradually from tissues to blood stream
Used as spinal and topical anesthesia.

Question 13

Cocaine

Answer 13

Only naturally occurring ester based local
Medium potency and DOA
inhibits catechlamine uptake peripherally and centrally (vasoconstriction and euphoria- cardiac toxicity)
Used as ophthalmic and topical anesthesia

Question 14

Lidocaine and Prilocaine

Answer 14

Amide based
Moderate hydrophobicity, large fraction of drug is in neutral form at physiologic pH= rapid onset, med DOA, and moderate potency
Metabolism by live by P450
Used for peripheral nerve blocks, epidural, spinal, and topical anesthesia.
Toxicities- CNS depression and cardiotoxicity

Question 15

Prilocaine

Answer 15

vasoconstricive

Question 16

Lidocaine

Answer 16

antiarrhythmic

Question 17

Bupivicaine

Answer 17

Amide based
long DOA and highly hydrophobic (high potency)
Metabolized by live P450
R and S enatiomer
Cardiac toxicity due to blocking Na channels in cardiac myocytes during systole but is slow to dissociate during diastole.

Question 18

Articaine

Answer 18

Amide based
Exhibits an ester group making it act differently
Partially metabolized in the plasma by cholinesterase and in the liver by P450

Question 19

Administration- topical

Answer 19

applied to skin or mucous membranes, short term relief, absorbed rapidly into circulation,
Ex- TAC, EMLA, and lidocaine patch

Question 20

Administration- infiltration

Answer 20

Used to number area of skin of mucosal surface via an injection. Kept at acidic pH to help absorption
Ex- lidocaine, procaine, bupivicaine

Question 21

Administration- peripheral nerve block

Answer 21

Injected percutaneous

Question 22

Administration- central nerve block

Answer 22

Drug delivered near spinal cord (epidural or intrathecal) Bupivicaine used in labor, ropivicaine and levobupivicaine due to not having cadiotoxicity

Question 23

Administration- intravenous regional

Answer 23

Beir’s block occasionally used in arm and hand surgery

Question 24

Toxicities

Answer 24

Hypersensitivity rxn- rare usually have sulfa drug allergy
Local irritation due to local application
CNS- extreme excitement followed by depression
Cardiac- effects on Na, K, and Ca channels lead to potential toxicity
Peripheral vasculature and bronchial smooth muscle- initial constriction followed by dilation.