local anesthetics

Question 1

What are the three structural components of local anesthetics?

Answer 1

aromatic ring
amino acid that can accept a proton (allowing the drug to change from hydrophilic to hydrophobic)
linker region (either an ester or an amide)

Question 2

What is the mechanism of action of local anesthetics?

Answer 2

Block voltages gated Na+ channels

Question 3

What are the two routes to the binding site for local anesthetics?

Answer 3

cytoplasmic route (main route) - protonated/hydrophilic form of drug enters the Na+ channel from the cytoplasmic side
plasma membrane route - deprotonated/hydrophobic form of drug enters the Na+ channel through the plasma membrane

Question 4

What are the major adverse effects of local anesthetics?

Answer 4

CNS effects - drowsiness -> dizziness -> twitching -> seizures -> coma
cardiovascular effects - decreased cardiac excitability and conduction velocity ->
CV effects usually occur before CNS effects

Question 5

Why is a vasoconstrictor (e.g. epinephrine) injected in conjunction with a local anesthetic?

Answer 5

Because local anesthetics are potent vasodilators but vasodilation facilitates the movement of drug away from site of injection, decreasing the drugs effect and increasing risk of systemic side effects.
Vasoconstrictors prolong the drug at its site of injection

Question 6

How is the metabolism of ester local anesthetics different from the metabolism of amide local anesthetics?

Answer 6

esters - local metabolism to PABA

amides - metabolism in the liver

Question 7

What drugs are in the ester class of local anesthetics? Amide class?

Answer 7

ester local anesthetics:
cocaine, procaine (novocaine), tetracaine, benzocaine
Amide local anesthetics:
lidocaine, prilocain, bupivicaine, ropivacaine

Question 8

Which local anesthetics can only be used in topical formulations?

Answer 8

cocaine (because of the abuse potential) and benzocaine (because it has only a hydrophobic form)

Question 9

Which local anesthetic is also used to treat cardiac arrhythmias?

Answer 9

lidocaine

Question 10

Which local anesthetic is uniquely a vasodilator and thus does NOT need to be injected with epinephrine?

Answer 10

prilocaine

Question 11

Which local anesthetic is associated with an increase in methemoglobinemia?

Answer 11

prilocaine