Kruse: Local Anesthetics

Question 1

Allergic reactions to what type of local anesthetics is most common due to metabolism to allergy-causing compounds?

How can you tell the type of local anesthetic based on its name?

Answer 1

Ester-type (i.e., benzocaine, cocaine, procaine, and tetracaine)

*Will only have one‘i’ in the name; while amides will have at least two ‘i’s

Question 2

Which local anesthetics are more prone to hydrolysis and as a result generally have a shorter duration of action?

Answer 2

Ester-type

Question 3

Use of which substances will reduce systemic absorption of local anesthetics and is useful for those drugs with intermediate or short durations of action (ie., prolongation of action)?

Answer 3

Vasconstrictors (i.e., epinephrine)

Question 4

How does the metabolism of ester-type local anesthetics differ from the amide-type?

Answer 4

• Ester-type are metabolized in plasma
• Amide-type are metabolized in liver and then excreted in urine as charged substances (CYP450)

Question 5

What is the MOA of local anesthetics?

Where is their receptor site located?

Answer 5

- Block voltage-gated Na⁺ channel currents and stop spread of AP’s across nerve axons

• Receptor site is at inner vestibule of the sodium channel

Question 6

What structural properties of some local anesthetics cause a faster rate of interaction with the sodium channel and more potent actions?

Answer 6

Smaller and more lipophilic

*Tetracaine, bupivacaine, and ropivacaine

Question 7

Which is affected first by local anesthetics injected into a bundle of large mixed nerves (sensory or motor)?

Answer 7

Motor nerves

Question 8

What is intravenous regional anesthesia (Bier block) used for?

How is it done?

Answer 8

• Used for short surgeries (<60 min) involving UE and LE’s
• IV injection of agent is placed in a distal vein while circulation of limb is isolated w/ a proximally placed tourniquet
• Large doses of local anesthetic used; tourniquet remains in place to prevent high circulating drug levels causing systemic effects

Question 9

Which local anesthetic potentiates the effect of NE on α-adrenergic receptors by blocking NET and results in localized vasoconstriction?

Answer 9

Cocaine

*Eliminates need for combining the drug w/ epinephrine

Question 10

Epinephrine administration to prolong the action of local anesthetics should never be injected into what tissues?

What could this result in?

Answer 10

• Those supplied by end arteries
• Fingers, toes, nose, and penis
• Vasocontriction could cause gangrene

Question 11

What are the early signs of CNS toxicity caused by local anesthetics?

Answer 11

- Circumoral and tongue numbness

- Metallic taste

Question 12

High concentrations of local anesthetics in the CNS may have what adverse effects?

Answer 12

• Nystagmus
• Muscular twitching
• Convulsions
• Death by respiratory failure

Question 13

When large doses of local anesthetics are required premedication with parenteral _____________ can provide prophylaxis against CNS toxicity by raising the seizure threshold

Answer 13

Benzodiazepine (diazepam or midazolam)

Question 14

Local anesthetics block which ion channels in the heart and can have what adverse effects on the heart and blood pressure?

Answer 14

• Block cardiac sodium channels
• Decrease electrical excitability, conduction rate, force of contraction
• Arteriolar dilation —> sytemic hypotension

Question 15

Cocaine is an exception to the local anesthetic effects on the heart, and instead can cause what?

Answer 15

• Vasconstriction –> local ischemia
• HTN
• Cardiac arrhythmias

Question 16

Which local anesthetic is the most cardiotoxic due to its long duration of action?

Answer 16

Bupivacaine

Question 17

Which local anesthetic is a Class Ib antiarrhythmic?

Answer 17

Lidocaine

Question 18

What are the effects of Lidocaine on the heart?

Answer 18

• Suppresses automaticity of condunction tissue by increasing electrical stimulation threshold of ventricle, His-Purkinje system, and spontaneous depolarization of the ventricles during diastole
• Blocks both the initiation and conduction of nerve impulses by decreasing the neuronal membrane’s permeability to sodium ions, which results in inhibition of depolarization w/ resultant blockade of conduction

Question 19

What is Benzocaine used for?

Answer 19

• Only as topical agent
• Dermatologic conditions, hemorrhoids, premature ejaculation, and as anesthetic lubricant (i.e., NG an endoscopic tubes/catheters)

Question 20

Cocaine, as a local anesthetic, is used primarily how?

Answer 20

Topical anesthtic of the upper respiratory tract

Question 21

What is Lidocaine used for clinically?

Answer 21

• Alternative choice for pt’s with allergy to ester-type local anesthetics
• Antiarrythmic agent

*Faster, more intense, longer acting, and more extensive anesthesia than an equal dose of Procaine

Question 22

What is Procaine used for clinically?

Answer 22

Only for infiltration anesthesia (local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings)

Question 23

Which local anesthetic is metabolized to a para-aminobenzoic acid, which inhibits the action of sulfonamide antibiotics?

Answer 23

Procaine

Question 24

Low concentrations of local anesthetics may produce which adverse effects on the CNS?

Answer 24

• Sleepiness (*CIS Q)
• Light-headedness
• Visual and auditory disturbances
• Restlessness

Question 25

Which local anesthetic is for surface use only?

Answer 25

Benzocaine

*i.e., someone comes in with bad road rash or something

Question 26

Which 3 local anesthetics have long durations of action?

Answer 26

1. Bupivacaine
2. Ropivacaine
3. Tetracaine

Question 27

Which local anesthetic has a short duration of action; used only for infiltration anesthesia?

Answer 27

Procaine