Local Anesthetics Flashcards
What is the MOA/ pharmacodynamics of Bupivicane?
- Blocks Na+ channels in nerve cells while in the closed/ inactive state preventing depolarization and impulse transmission
- Holds the nerve under threshold, thereby decreasing the chance of action potential
What is the drug class/ chemical structure of Bupivicaine?
- Bupivacaine is an aminoamide local anesthetic
- Bupivacaine is a Pipecoloxylidide.
- Adding a butyl group to a Mepivicaine makes Bupivacaine and makes it 35x more lipid soluble (potent) and has a longer DOA
- All local anesthetics consist of a lipophilic end and a hydrophilic end separated by a hydrocarbon chain. The lipophilic end is essnetial for anesthetic activity. Esters have a -CO and Amides have a -NH froup linking hydrocarbon to the lipophilic aromatic ring.
What are the side effects of Bupivacaine?
- differential blockade (desired in many cases)
- highly CV toxic
- TNS
- Cauda equina syndrome
- Allergy- rare. If there is an allergy it’s more likely to be the preservative (methylparaben) than the drug itself.
- Vasodilator
- Direct IV injection of Bupivacaine can lead to sudden cardiovascular collapse
When is Bupivacaine contraindicated?
- Pt. refusal
- Inability to cooperate
- Coagulopathies
- Hypovolemia
- Infection at site of injection
- Inexperience of clinician
- Caution with meds like Cimetidine and Propranolol which inhibit CYP450 system and could help produce Bupivacaine toxicities.
What is the dose of Bupivacaine?
- Max Dose: 2.5mg/kg
- Epidural:
- 0.25%- 0.5%
- 15-50mL
- DOA 3-5 hrs
- Spinal
- 0.5% (Isobaric)-0.75%(Hyperbaric)
- 15-20mg total
- Lasts 1.5hrs- 3hrs
- PNB- minor
- 0.25%-0.5%
- 15-20mL
- DOA 3-6hrs, 4-7hrs w/ epi
- PNB- major
- 0.25%-0.5%
- 30-50 mL
- DOA 6hrs- 12hrs
- Onset: 20-30 mins
What are the pharmacokinetics of Bupivacaine (how is it metabolized)?
- Bupivacaine is an amide local anesthetic. Amides are transported to the liver and metabolized by the CYP450 system. Intial metabolism converts LA to an amino caroboxylic acid before eventual N-dealkylation and subsequent hydrolysis of the drug. This process takes longer than ester metabolism, which takes place in the blood. Therefore amides have longer elimination 1/2 times and a higher risk for systemic toxicity.
- There is some uptake into the lungs
- Metabolism is dependent on hepatic blood flow
What is the MOA/ pharmacodynamics of Lidocaine?
- Blocks Na+ channels in nerve cells while in the closed/ inactive state preventing depolarization and impulse transmission
- Holds the nerve under threshold, thereby decreasing the chance of action potential
What is the drug class/ chemical structure of Lidocaine?
- Lidocaine is an aminoamide local anesthetic.
- All local anesthetics consist of a lipophilic end and a hydrophilic end separated by a hydrocarbon chain. The lipophilic end is essnetial for anesthetic activity. Esters have a -CO and Amides have a -NH froup linking hydrocarbon to the lipophilic aromatic ring.
What are the side effects of lidocaine?
- TNS
- High incidence of Cauda Equina syndrome (do not use 5% lidocaine in continuous spinal infusion)
- CV toxicity
- vasodilation
What are the contraindications to lidocaine?
- Pt. refusal
- Inability to coooperate
- Coagulopathies
- Infection at side of injection
- Hypovolemia
- Inexperience of clinician
What is the dose of Lidocaine?
- Max Dose= 4mg/kg; 7mg/kg w/ epi
- Epidural
- 1-2%
- 15-30mL
- Onset: 5-15 min
- DOA: 1.5-2hrs
- Spinal
- 1.5-5% (hyperbaric)
- 1-2mL
- DOA: 30min - 90min
- PNB- minor
- 1%
- 5-20mL
- DOA: 1-2 hrs, w/ epi: 2-3hrs
- PNB- major
- 1-2%
- 30-50mL
- Onset: 10-20min
- DOA: 2-4 hrs
How is Lidocaine metabolized, what are the pharmacokinetics?
- Lidocaine is an amide local anesthetic. Amides are transported to the liver and metabolized by the CYP450 system. Intial metabolism converts LA to an amino caroboxylic acid before eventual N-dealkylation and subsequent hydrolysis of the drug. This process takes longer than ester metabolism, which takes place in the blood. Therefore amides have longer elimination 1/2 times and a higher risk for systemic toxicity
- There is some uptake into the lungs which acts as a reservoir and should help prevent toxicity
- Metabolism is dependent on hepatic blood flow
What are signs and symptoms of local anesthetic toxicity?
- circumoral numbness
- ringing in the ears
- metallic taste
- vision changes
- dizziness
- slurred speech
- reslessness
- twtiching in teh face then extremities (indicative of impending seizures)
- hypotension
- arrhythmias
- decreased SVR and CO
- wide QRS and PRI
- myocardial depression
- CV arrest
What is the pKa of Lidocaine?
7.9- fast onset
At physiological pH, what % of Lidocaine is ionized? unionized?
- Ionized- 76%
- unionized- 24%
What is the % protein binding of Lidocaine?
65%- moderate DOA
What is the E 1/2 t of Lidocaine?
Typically 96 mins.
What are the 2 active metabolites of Lidocaine?
- Xylidide
- Monoethylglycinexylide
What is the mechanism of action/ Pharmacokinetics of Procaine?
- Blocks Na+ channels in nerve cells while in the closed/ inactive state preventing depolarization and impulse transmission
Holds the nerve under threshold, thereby decreasing the chance of action potential
What is the drug class/ chemical structure of Cocaine?
- Cocaine is an aminoester local anesthetic
- It is an ester of benzoic acid
What are the side effects of Cocaine?
- Euphoria
- Coronary vasospasm
- Myocardial ischemia
- Ventricular arrhythmias
- HTN
- tachycardia
- increased myocardial O2 demand
- SNS stimulation (blocks the reuptake of NE & Dopa
- It is the only local anesthetic that is a potent VASOCONSTRICTOR
- Causes a dose dependent decrease in uterine bloodflow and fetal hypoxemia
What are the contraindications to using Cocaine?
- Cocaine is contraindicated in most every case aside for sinus surgery or ENT cases where vasoconstriction is desired
- It is only used in patients with CV stability.
What is the dose of Cocaine?
- Max dose: 3mg/kg
- it is only used topically
What are the pharmacokinetics of Cocaine/ how is it metabolized?
- Cocaine is an ester local aneshetic; however, it has a unique metabolism.
- It is the only ester that is metabolized in the liver by liver esterases and the CYP450 system.
- It’s water soluble metabolites are excreted in the urine
What is the DOA of Cocaine?
30-40 min after intranasal application, 5min after IV or smoked.
What is the MOA/ pharmacodynamics of Procaine?
- Blocks Na+ channels in nerve cells while in the closed/ inactive state preventing depolarization and impulse transmission
Holds the nerve under threshold, thereby decreasing the chance of action potential
What is the drug class/ chemical structure of procaine?
- It is an aminoester local anesthetic
- It is the ester protype
What are the side effects of Procaine?
- Procaine is not used topically
- Procaine is not used for Bier blocks
- Procaine is not used in epidurals
- If allergy suspected, it is unlike due to the drug, but rather to PABA (para aminobenzoic acid), an intermediary in ester hydrolysis
- If allergy to esters is supected, it is OK to give amides.
- LA toxicity
- vasodilation
- High incidence of nausea
- Pseudocholinesterase deficiency or anticholinesterase drugs can increase the risk of system toxicity of esters.
- Metabolite of procaine interferes with the efficacy of sulfanoamide antibiotics
- Not currently a favorite due to slow onset and short DOA
What are the contraindications of Procaine?
- Not for Bier blocks
- Not for epidurals
- Not for topical use
- Pt. refusal
- inability to coooperate
- coagulopathies
- hypovolemia
- infection at site of injection
- inexperience of clinician
What is the dose of procaine?
- Max dose- 7mg/kg
- Epidural
- procaine not used in epidurals
- Spinal
- PNB-minor
- PNB-major
How is Procaine metabolized, what are the pharmacokinetics?
- Procaine is an ester local anesthetic. It is metabolized by plamsa esterases in the blood.
- PABA is an intermediary in ester metabolism and can cause allergy.
- Caution in patients with pseudocholinesterase definciency or those on anticholinesterase drugs.
What is the pKa of Procaine?
8.9
What is the % ionized of Procaine? % unionized?
- ionized- 98%
- unionized- 3%
What is the E 1/2 t of Procaine?
9 minutes