Locals

Question 1

Lidocaine

Answer 1

Amide Local Anesthetic
Anti-arrhythmic class 1B

Use;

• regional anesthesia to block transmission of nerve signals to prove analgesia without loss of consciousness
• ACLS pathway for pulseless VFib and VT
• attenuates the response to intubation
• post op IV dose; analgesia to decrease opioid use

MOA; Blocks VGNaChannel in nerve cell membrane while in closed inactive state; prevents depolarization and impulse transmission

Anti-arrhythmic MOA;

• blocking of Na channels in cardiomyocytes by monoethylglycinexylidide
• shortens the action potential duration and refractory period preventing reentry dysrhythmias such as PVCs and VT

Dose;
Blunt SNS response; 1 mg/kg

Arrhythmias; 2 mg/kg followed by infusion 1 - 4 mg/min

ACLs; 1.5 mg/kg q 3 - 5 min to max of 3 mg/kg

LA max dose 4 mg/kg or 7mg/kg with epi

Spinal; 1 - 2 ml or 30 - 100 mg

Pharmacokinetics;
-onset; Rapid

• E1/2 time; 90 min (up to 8 hours for active metabolite)
• DOA; 1 - 2 hours (increase DOA with epi)
• Vd; 91 L
• Pb; 65- 70% (LA)
• Pb; 55% (anti arrhythmic)
• metabolized by liver via CYP450 system
• metabolism is BF dependent (propranolol, VA and cimetidine can decrease clearance)
• pt at risk for toxic build up in liver failure

*active metabolite; monoethylglycinexylidide then hydrolyzed to xylidine
Monoethy; E1/2t is longer *anti-arrhythmic

Elimination; very little excreted unchanged by the kidneys

Side Effects;
-allergic reactions are rare with amide LA

• TNS (transient neurological symptoms); neuroinflamm in buttock, lower back, post thighs 3-6 hrs after recovery
• Cauda equina syndrome; diffuse lumbosacral injury, can cause paraplegia w/ 5% Lido

Lidocaine;
> 5 mcg/ml Systemic toxicity begins at plasma conc.
may result in prolonged P-R interval and QRS complex

• 5-10 mcg/ml: LA toxicity circumoral numbness, lightheadedness, tinnitus, skeletal muscle twitching, visual disturbances, tachycardia, systemic hypotension, myocardial depression, decreased SVR, cardiac output.
• 10-15 mcg/ml: seizures, unconsciousness
• 15-25 mcg/ml: apnea, coma

Contraindications;- Coagulopathy

• infection
• hypovolemia
• hypersensitivity

caution in impaired hepatic function; decrease dose

Question 2

Bupivacaine

Answer 2

Amide Local Anesthetic

MOA; hold VGNa channel in closed inactive state and prevents depolarization and impulse transmission

Uses; Regional anesthesia; provides analgesia without LOC

• good differential nerve block
• epidural, spinal, OB

LA max Dose; 2.5 mg/kg
Spinal; 2 - 3 ml or 15 - 20 mg

Pharmacokinetics;

• Onset; moderate
• E1/2 time; 3.5 hours
• DOA; long
• Pb; 95%
• high lipid solubility (30)
• Pka; 8.1
• % nonionized; 17

metabolism; CYP450 enzymes; blood flow dependent (propranolol, VA and cimetidine decrease clearance)
*decrease dose in liver failure; risk of toxic build up

Side effects;

• minimal. risk of anaphylaxis (> risk with Ester LA)
• LA toxicity; circumoral numbness, lightheadedness, vision changes, ringing in ears, slurred speech; leads to CNS changes, seizure, apnea
• Transient neurological symptoms (TNS)
• cauda equina syndrome
• myocardial depression, increased HR, decreased BP, SVR, CO
• *bupivacaine is the most CV toxic r/t affinity for receptors

Contraindication; infection, coagulopathy, hypovolemia,

Question 3

Cocaine

Answer 3

Ester Local Anesthetic

Uses;

• Ophthalmic & ENT surgery to cause vasoconstriction and reduce bleeding
• topical anesthetic used for suturing small cuts

MOA;

• blocks the VGNA channels in the closed inactive state and block initiation and conduction of nerve impulses by deceasing the membranes permeability to sodium ions; blocking depolarization
• blocks uptake of NE; producing vasoconstriction, tachycardia and HTN

Max Dose; 1.5 - 3 mg/kg

Pharmacokinetics;

• onset; 1 min
• peak; 5 min
• E1/2t; 75 min
• DOA; dose dependent (>30min)

metabolized by plasma and liver cholinesterase
10% excreted unchanged in the urine

*CYP450 INHIBITOR

Side Effects;

• CV toxicity (small doses; Bradycardia/large doses tachycardia)
• HTN
• V Tach/ V-Fib
• Myocardial depression
• cardiac arrest
• Tachyphylaxis (recreational use can have implication on effects of ketamine, ephedrine)

Contraindications;

• CAD
• MI
• CHF
• arrhythmias
• HTN
• MAOi
• Pregnancy

Caution
-decreased plasma cholinesterase activity