Pharmacology of Local Anesthetics

Question 1

What is the mode of action of Local anesthetics?

Answer 1

• Decrease rate of depolarization
• keep the depolarization from reaching firing threshold
• keep impulse from propagating

Question 2

Because local anesthetics are weakly basic what is added to them to make them water soluble and more stable?

Answer 2

acids (most commonly HCL)

Question 3

What two forms of the local anesthetic exist in the tissue?

Answer 3

1-Unchaged molecules (RN) base

2-Positively charged molecules (RNH+) cation

Question 4

Which form of local anesthetic diffuses through the nerve sheath?

Answer 4

uncharged (RN) base form

Question 5

What is the difference between normal tissue and infected tissue in regards to anesthesia profusion?

Answer 5

Normal tissue pH is around 7.4 and RN can readily diffuse. Infected tissue is much more acidic which favors RNH+ and results in poor diffusion into the nerve sheath

Question 6

What clinical side effect will the patient feel because of the acidified local anesthetic?

Answer 6

Burning sensation when being injected

*LAs are acidified to prevent oxidation of vasoconstrictor

Question 7

Local anesthetics increase the threshold for neuroelectric excitation and block what?

Answer 7

Pain
Cold
Warm
Touch
Some pressure

Question 8

Local anesthetics cross the BBB, cross the placenta and subject highly perfused tissues to potential overdose and toxicity. Which tissue has the highest level and is the largest mass in the body?

Answer 8

Skeletal Muscle

Question 9

Where are amides metabolized?

Answer 9

Almost entirely in the liver

*prilocaine is partially metabolized in the lungs as well

Question 10

O-toluidine is a metabolic by-product of what and can lead to what?

Answer 10

Prilocaine, can lead to methemoglobinemia (tissue hypoxia)

Question 11

Amide half lifes are between ______ and esters are between_______

Answer 11

90-160 min
0.1-0.7 hours (6-42 min)

*Local anesthetics are excreted via renal clearance

Question 12

Which type of local anesthetics are potent vasodilators (except for 1) and are metabolized by plasma pseudocholinesterases?

Answer 12

Amino Esters (Esters)

Question 13

What are 5 examples of Esters?

Answer 13

1-Benzocaine (topical)
2-Chloroprocaine
3-Cocaine (vasoconstrictor)
4-Procaine (use for vasodilation when intra-arterial LA injection)
5-Tetracaine

Question 14

What are three reasons vasoconstrictors added to Local anesthetics?

Answer 14

1-They decrease perfusion and Cardiovascular adsorption
2-More LA enters the nerve (longer lasting anesthesia)
3-Decrease bleeding at injection site

Question 15

What are three different types of vasoconstrictors?

Answer 15

1-Epinephrine
2-Norepinephrine
3-Levonordefrin

*Act on adrenergic receptors.

Question 16

1:1000 dilution means what for vasoconstrictors?

Answer 16

1g is in 1000 ml (1mg/ml)

Question 17

a 2% anesthetic means how much is there?

Answer 17

2g/100 ml (20 mg/ml)

Question 18

If 100 patients are given 2 % lidocaine (1:100,000 epi) _____% will last 60 minutes, _____%more than 60 and ___% less than 60

Answer 18

70, 15, 15

Question 19

What are the 5 main local anesthetics used?

Answer 19

1-2% Lidocaine 1:100,000
2-3%Mepivacaine plain (Carbocaine)
3-4% Articaine 1:100,000 (Septocaine
4-4% Prilocaine Plain (Citanest)
5-0.5% bupivocaine 1:200,000 (Marcaine)

Question 20

Which LA has a red line, peak onset around 5 min, lasts 90-120 min, max does of 300 mg per appt and is a pregnancy cat B, And is also the preferred anesthetic for Pediatric and pregnant?

Answer 20

2% Lidocaine 1:100,000

*dose by wt: 4.4 mg/kg or 2.0 mg/lb. Max epi 0.2 mg/appt (healthy) 0.04 mg/appt (CV patient) Max 300 mg LA/appt

Question 21

Which LA has a gold line near the plunger, no epi, onset of 30-120 sec (upper max) 1-4 min (lower jaw), lasts 20 min (upper) 40 min (lower) and is a pregnancy cat C and can be used as an alternative when epi is a problem?

Answer 21

3% Mepivacaine plain (Carbocaine)

*dose by wt: 4.4 mg/kg or 2.0 mg/lb. 300 mg max LA/appt

Question 22

Which LA has a gold band near the needle, onset in 1-6 min, lasts around 1 hour, is a pregnancy Cat C, and is used when lidocaine isn’t getting the patient numb?

Answer 22

4% Articaine 1:100,000 (Septocaine)

*dose by wt: 7.0 mg/kg or 3.2 mg/lb. Max epi 0.2 mg/appt (healthy) 0.04 mg/appt (CV patient) Max 400 mg LA/appt

Question 23

Which LA has a black band, no epi, onset of 2-3 min, complete anesthesia for 20 minutes, 2.5 hour IA, Is metabolized in the liver and lungs (0-toluidine toxic metabolite) and is a pregnancy cat B?

Answer 23

4% Prilocaine plain (Citanest)

*dose by wt: 6.0 mg/kg or 2.7 mg/lb. Max 400 mg LA/appt

Question 24

Which LA has a blue line, onset in 1-17 min, lasts 2-9 hours, is very cardiotoxic, is a pregnancy cat C, and is used for prolonged anesthesia?

Answer 24

0.5% Bupivicaine 1:200,000 (Marcaine)

**dose by wt: 1.3 mg/kg or 0.6 mg/lb. Max 90 mg LA/appt. Never use in children, adolescents or pregnant patients

Question 25

4% Prilocaine plane has been associated with Methemoglobinemia cause by the O-toluidine byproduct doing what?

Answer 25

Oxidizing hemoglobin (Fe2+, ferrous) to methemoglobin (Fe3+, ferric) resulting in less oxygen to tissues

*treated with Methylene blue IV solution and O2