Tox: local anesthetics

Question 1

Examples of esters and amides

Answer 1

Amides (have 2i’s): lidocaine, bupivacaine, mepivacaine

Esters: cocaine, benzocaine, tetracaine, procaine

Question 2

MOA of local anesthetics

Answer 2

Inhibition of Na channels -> reversible blockade of action potential along affected nerve.
Systemic toxicity -> accumulation in brain, cardiac tissue where it causes toxicity by blocking Na+channels/APs

Question 3

Symptoms of local toxicity

Answer 3

Prolonged anesthesia, permanent sensory/motor deficits, respiratory arrest secondary blocking nerves to resp muscles

Question 4

Symptoms of systemic toxicity

Answer 4

Neuro:
- Tinnitus.
- Numbness of mouth.
- Confusion, anxiety, sense impending doom, HA, drowsiness, dizziness, tremors.
-Seizures.
Cardiac:
- widening PR interval, QRS, bradycardia, VT, VF, hypoTN, asystole
- Methemoglobinemia with exposure to benzocaine, prilocaine
- Hemodynamic collapse.

Question 5

What population is particularly at risk for cardiotoxicity from bupivacaine?

Answer 5

Pregnant women

Question 6

Treatment of local anesthetic toxicity

Answer 6

Intralipid (IV fat emulsion): acts as lipid sink, pulling local anesthetics from site of toxicity
- Give 20% solution 1.5cc/kg bolus then 0.25cc/kg/min over 30-60min.

Supportive:

• Benzos for seizures
• Methylene blue for methemoglobinemia

Question 7

If a patient has an allergy to an ester, can you give an amide and vice versa?

Answer 7

Yes. Hypersensitivity reaction to either an ester or amide should NOT cross-react with the other

Question 8

Which group of local anesthetics cause most allergic reactions?

Answer 8

Esters, due to production of metabolite, paraaminobenzoic acid (PABA).
Note that multi-dose bottles of amide contain preservative methylparaben which is chemically related to PABA.