Pharm - Local Anesthetics - Kisby

Question 1

What is the primary determinant of the onset of action of a LA?

Answer 1

Its pK!

Question 2

What determines potency of an LA?

Answer 2

Lipid solubility (positive correlation) as determined by aromatic side chain

Question 3

What determines duration of action of an LA?

Answer 3

• Amide containing LAs (vs esters) are more stable → longer duration of action
• Hydrophilic amine interaction w/channel proteins also influences duration of action

Question 4

What is the MOA of nerve blocks?

Answer 4

• Cause reversible block of nerve conduction through LA interaction w/Na channels
• Blocking 2-3 nodes of Ranvier is required to inhibit transmission

Question 5

What are some SEs of LAs?

Answer 5

• CNS depression (at low dose)
• Excitation and seizures (at high dose)
• CV effects

Question 6

Which LAs cause allergies and which don’t?

Answer 6

• Aminoesters (procaine, etc.) are known dermatitis causing allergens
• Aminoamide LAs very rarely cause allergic reactions

Question 7

Aminoesters

Answer 7

• Drugs: cocaine, procaine, tetracaine, chloroprocaine, benzocaine
• Rapidly hydrolyzed by pseudo-cholinesterases
• Para-aminobenzoic acid (PABA) causes allergies

Question 8

Cocaine HCl

Answer 8

• Only LA with sympathomimetic effects (vasoconstriction & tachycardia)
• Use: topical to control bleeding after ENT procedures

Question 9

Procaine

Answer 9

• Low potency & short duration

* Metabolized to PABA (so may cause allergic reactions)

Question 10

Aminoamides

Answer 10

• Drugs: lidocaine, mepavicaine, prilocaine, bupivicaine, ropivicaine, etidocaine, levobupivicaine
• Metabolized to inactive metabolites → liver impairement
• Allergic reactions are rare

Question 11

Lidocaine

Answer 11

• Intermediate duration
• Use: short-duration procedures (ex: epidural), topical, cardiac (anti-arrhythmic agent), pediatric (for venipuncture, IV cannulation & dental procedures)

Question 12

Prilocaine

Answer 12

• Intermediate duration

* Use: topical & infiltration anesthesia

Question 13

What is methemoglobinemia and what is its tx?

Answer 13

• Caused by high concentrations of amino amide LAs
• Causes cyanosis, decompensation in CV or pulmonary disease pts
• Tx: IV methylene blue

Question 14

Would an ionized or unionized LA perfuse the tissue better?

Answer 14

Unionized