Exam 3: Local anesthetics

Question 1

What part of the pain pathway do local anesthetics work to block?

Answer 1

Prevent transmission of the pain

Question 2

What is the distinguishing characteristic of local anesthetics?

Answer 2

ability to provide complete loss of all sensory modalities

Question 3

What part of a neuron does a local anesthetic act to block?

Answer 3

sodium channels helping to carry an action potential down the axon

Question 4

What are the three structural components of local anesthetics?

Answer 4

Hydrophobic component, intermediate linker component, hydrophilic component

Question 5

What does the hydrophobic component of an anesthetic do?

Answer 5

Increases potency, plasma protein binding, increases duration of action, increases toxicity

Question 6

What is usually the structure of the hydrophobic component of an anesthetic?

Answer 6

aromatic ring

Question 7

What are the two linker classes of an anesthetic?

Answer 7

Ester bone and amide bond

Question 8

What determines the metabolic fate of a local anesthetic?

Answer 8

the linker component (esters are rapidly broken down in plasma, esters have higher potential for allergic sensitization)

Question 9

What are does the hydrophilic component of an anesthetic do?

Answer 9

determines the dissociation constant, impacts the onset of action

Question 10

What is the structure of a hydrophilic component of an anesthetic usually?

Answer 10

An amine

Question 11

Are local anesthetics weak acids or weak bases?

Answer 11

Weak bases, pK= 8-9

Question 12

When are weak bases ionized, when are they un-ionized?

Answer 12

ionized in acidic environments, unionized in basic environments

Question 13

What form (ionized or not) of an anesthetic can cross a cell membrane?

Answer 13

unionized

Question 14

What form of an anesthetic (ionized or not) can act on the sodium channels to block them?

Answer 14

ionized

Question 15

Do higher or lower pK drugs have a more rapid onset of action? Why?

Answer 15

Lower pK, more uncharged form of drug at physiological pH (more can enter the cell quickly)

Question 16

What state of a sodium channel (resting, open, inactive) do drugs have an affinity for?

Answer 16

High affinity for open or inactive states, forcing them to stay in the inactive state

Question 17

What nerves do local anesthetics preferentially block?

Answer 17

Nerves that have a higher rate of depolarization and smaller diameter, myelinated nerves before unmyelinated

Question 18

What is the order in which sensations are affected with local anesthetics

Answer 18

Pain, cold, warmth, touch, deep pressure, motor function

Question 19

T/F: LAs can increase vasodilation

Answer 19

True

Question 20

What are adverse effects of LAs on CNS?

Answer 20

tongue numbness, dizziness, visual disturbances, tinnitus, slurred speech, convulsions, eventual coma

Question 21

What are adverse effects of LAs on the cardiovascular system?

Answer 21

hemodynamic instability, decreased myocardial electrical excitability, cardiovascular collapse

Question 22

What linker region is associated with hypersensitivity? why?

Answer 22

ester LAs because of para-aminobenzoic acid (PABA), which is a metabolite of esters

Question 23

What is the absorption of LAs determined by?

Answer 23

dose, vascularity of target, drug tissue binding

Question 24

What can be used to decrease systemic absorption of LAs?

Answer 24

epinepherine (vasoconstrictor), helps to keep a higher local concentration

Question 25

What can affect local distribution of LAs?

Answer 25

pH of the local tissue- inflamed tissues and infection often have a lower pH

Question 26

Where are esters and amides metabolized respectively?

Answer 26

esters in plasma by pseudocholinesterase, amides in liver by oxidases

Question 27

What is EMLA?

Answer 27

Eutectic mixture of local anesthetics, exists as an oil at room temp so it penetrates in tact skin, effective for procedures such as lumbar punctures

Question 28

What is infiltration anesthesia used for? What is its route?

Answer 28

Subcutaneous injection, used for minor surgery and dental procedures

Question 29

What is a nerve block for? What is its route?

Answer 29

Injection at base of digit or larger volume into brachial plexus, Major or minor block of peripheral nerve conduction

Question 30

What is a Bier block?

Answer 30

IV injection of anesthetic + tourniquet to keep it there, used to anesthetize distal arm or leg, used in forearm, hand, sometimes distal leg and foot

Question 31

What is an epidural anesthesia?

Answer 31

Injection of LA into epidural space during labor and delivery, primarily acts on nerve roots, can go to blood so should use epinephrine to decrease peak plasma rates

Question 32

What is spinal anesthesia?

Answer 32

Injection into CSF in lumbar space, can anesthetize large amount of body, the density of the solution determines where it moves (more dense, it’ll travel down to caudal spinal cord)

Question 33

Describe procaine

Answer 33

Ester-type, short acting usually given with vasoconstrictor, rapid metabolism of plasma

Question 34

Describe lidocaine

Answer 34

Amide-type, metabolized in liver, overdose may cause death from v-fib

Question 35

Describe mepivacaine

Answer 35

Amide type, not effective topically, somewhat longer acting than lidocaine

Question 36

Describe bupivacaine

Answer 36

Amide type, long acting and potent LA, used for: regional and epidural blocks, prolonged surgery

Question 37

Describe ropivacaine

Answer 37

Amide-type, long acting LA, less CV and CNS toxicity than bupivacaine

Question 38

Describe tetracaine

Answer 38

Ester-type, used for topical anestheisa of eye, nose and throat and for spinal anesthesia

Question 39

Describe cocaine

Answer 39

ester-type, good penetration of tissues and its a vasoconstrictor, used for upper respiratory tract and mucosal membranes