Oral: Local Anesthetics

Question 1

Lidocaine: Drug Class

Answer 1

Class IB Na channel blocker (antiarrhythmic)
and
Amide Local Anesthetic

Question 2

Lidocaine: Pharmacokinetics

Answer 2

pKa 7.9 
23% non-ionized, low lipid solubility
Pb = DOA: 65%
Ls/Potency: Low/low
Onset: fast
DOA: 1-2hr (moderate)
Liver metabolism – CYP450 
Active metabolites: Xylidide (10%) and monoethylglycinexylidide (80%)
Elimination 1/2t: antiarrhythmic: 1-8 hrs; LA 90 min

Question 3

Lidocaine: Side Effects

Answer 3

1. LA toxicity (CNS > CV collapse)
2. Methemoglobinemia toxicity
3. Cauda Equina Syndrome
4. Anterior spinal artery syndrome
5. Allergic reaction (rare)

Question 4

Lidocaine: Contraindications

Answer 4

Hypersensitivity to amide LAs and methemoglobinemia
Stokes-Adams syndrome,
Wolff-Parkinson-White syndrome
Coagulopathies, hepatic dysfunction, site infection

Question 5

Lidocaine: Dosing

Answer 5

Max: 4 mg/kg  + epi: 7 mg/kg

Blunt DVL: 1 mg/kg

Spinal MAX- 30-100mg

Epidural: 15-30 ml of 0.5-2%

Arrhythmia: 2 mg/kg + gtt: 1 – 4 mg/min

Question 6

Drug Class: LIDOCAINE, BUPIVICAINE, ROPIVICAINE

Answer 6

Amide Local Anesthetic / NA Channel Blocker

Question 7

MOA: All LAs or just LIDOCAINE, BUPIVICAINE, ROPIVICAINE?

Answer 7

Bind to alpha subunit of Na+ channels on the nerve cell membrane in the “inactivated closed state”

Stabilizes the inactive conformation of the channel = inhibits influx of Na ions -> blocks impulse conduction in the depolarization phase

Inhibit the nerves ability to reach the threshold for action potential propagation

Question 8

Bupivacaine: Pharmacokinetics

Answer 8

pKa: 8.1 
non-ionized: 17%
PB: 95%
Ls/Potency: High/high
Onset: 5min (moderate)
DOA: Long (4-8hrs)
CYP450 liver metabolism that depends on HBF, significant pulm 1st pass 
E1/2t: 3.5hrs

Question 9

Bupivacaine: Side Effects

Answer 9

1. Most cardiotoxic: use 0.5% or lower for epidural and PNB
2. Differential blockade
3. Transient neurologic symptoms (TNS)
4. Cauda Equina Syndrome

Question 10

Bupivacaine: Contraindications

Answer 10

Hypersensitivity to amide LAs
Bradycardia
Severe Hypotension/hypovolemia
Hepatic disease and/or decreases in hepatic blood flow
Coagulopathies
Extreme caution in poor CV function
Infection at site

Question 11

Bupivacaine: Dosing

Answer 11

Max 2.5 mg/kg

Spinal 15-20mg

Epidural 15-30 ml of 0.0625-0.5%

Question 12

Metabolism: LIDOCAINE, BUPIVICAINE, ROPIVICAINE

Answer 12

Liver metabolism – CYP450

Question 13

PK: ROPIVICAINE

Answer 13

pKa: 8.1 
non-ionized: 17%
PB: 95%
Ls/Potency: High/high
DOA: Long (4-8hrs)
CYP450 liver metabolism, 2 active metabolites 
E1/2t: 2hrs

Question 14

SE: ROPIVICAINE

Answer 14

1. LA tox (< bupiv)
2. differential block
3. TNS
4. Cauda Equina Syndrome

Question 15

CI: ROPIVICAINE

Answer 15

Coagulopathies, hypovolemia, infection at site

Question 16

Dose: ROPIVICAINE

Answer 16

Max 3.5 mg/kg

Spinal 15-20mg

Epidural 15-30 ml of 0.2-0.75%

Question 17

Class: CHLOROPROCAINE

Answer 17

Ester Local Anesthetic

Question 18

MOA: CHLOROPROCAINE

Answer 18

?

Question 19

PK: CHLOROPROCAINE

Answer 19

pKa: 8.7
non-ionized: 2%
PB: 7%
Ls/Potency: Low/low
Onset: Fast
DOA: Short (30 – 60 min) 
Hydrolyzed by  pseudocholinesterases

Question 20

SE: CHLOROPROCAINE

Answer 20

1. Preservative causes Cauda Equina
2. LA toxicity
3. Hypersensitivity

Question 21

CI: CHLOROPROCAINE

Answer 21

Coagulopathies, hypovolemia, infection at site

Question 22

Dose: CHLOROPROCAINE

Answer 22

Max 12 mg/kg

Spinal 300-900mg