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Questions and Answers
What is a common characteristic of all local anesthetics in terms of their mechanism of action?
Which local anesthetic is classified as having a long duration of action?
Which of the following local anesthetics belongs to the ester classification?
Which action does epinephrine serve when combined with local anesthetics?
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Which of the following is a significant property of amide local anesthetics?
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What is the primary excretory organ for local anesthetics and their metabolites?
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What is the proper classification of procaine based on its chemical structure?
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Which injectable local anesthetic is known for having the lowest incidence of allergic reactions?
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Which of the following anesthetics is classified as a surface anesthetic that is soluble?
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How long does it typically take for intravenous local anesthetics to achieve peak blood levels?
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What type of local anesthetic is articaine classified as?
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What is the primary site of biotransformation for amide local anesthetics?
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Which local anesthetic is primarily hydrolyzed in the blood plasma by the enzyme pseudocholinesterase?
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Which of the following is NOT a method of local anesthetic administration?
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In terms of uptake, which location has the slowest time to achieve peak blood levels for local anesthetics?
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What general effect do most local anesthetics have on blood vessels when injected?
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What is the primary effect of high blood levels of local anesthetics on the central nervous system?
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Which component of the local anesthetic solution is responsible for the blockade of nerve conduction?
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What is a characteristic of Procaine in terms of its pharmacological properties?
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What is the primary function of sodium chloride in local anesthetic solutions?
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Which local anesthetic is characterized as having a short onset of action?
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What happens to the cardiovascular system with overdose levels of local anesthetics?
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What role does the vasoconstrictor play in local anesthetic solutions?
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What is true about the metabolism of Procaine?
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What is the duration of pulpal anesthesia provided by 2% mepivacaine with a vasoconstrictor?
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Which of the following is a contraindication for the use of prilocaine?
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What is the maximum recommended dose of mepivacaine for adults?
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Which vasoconstrictor is commonly combined with 2% mepivacaine?
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What is the primary classification of prilocaine?
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What is the primary reason for combining procaine with propoxycaine?
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Which local anesthetic has a pregnancy classification of B, indicating it is safe during pregnancy?
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What is the maximum recommended dose of lidocaine with epinephrine for an adult patient?
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Which of the following anesthetics is primarily metabolized in the liver and can produce potentially toxic metabolites?
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Which local anesthetic has the shortest half-life and is metabolized by plasma?
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How does lidocaine compare to procaine in terms of potency?
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What is a significant difference between mepivacaine and procaine regarding their vasodilating properties?
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Which anesthetic is primarily used for immediate management of accidental intraarterial injection?
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Study Notes
Classification
- Local anesthetics are classified based on chemical structure (ester or amide), duration of action (short, intermediate, long), biological site and mode of action, and mode of application.
- Examples of esters: benzocaine, cocaine and procaine
- Examples of amides: lidocaine, mepivacaine, prilocaine and bupivacaine
- Short duration includes mepivacaine HCL 3%
- Intermediate duration includes lidocaine HCL 2% + epinephrine 1:1,00,000
- Long duration includes bupivacaine HCL 0.5% + epinephrine 1:2,00,000, and etidocaine
- Injectable local anesthetics include procaine and lidocaine
- Topical local anesthetics include soluble (cocaine, lidocaine) and insoluble (benzocaine)
- All local anesthetics use the same mechanism of action, which is blocking sodium channels on the nerve cell membrane
Pharmacokinetics of Local Anesthetics
- Uptake: Local anesthetics are absorbed into the blood, distributed throughout the body.
- Peak blood level: The highest concentration of drug in the bloodstream occurs 1 minute after intravenous administration, 5 minutes after topical, 5-10 minutes after intramuscular, and 30-90 minutes after subcutaneous
- Distribution: Highly perfused organs like brain, head, liver, kidneys, lungs and spleen have higher blood levels than less perfused organs. Skeletal muscle holds the largest percentage of local anesthetic due to its size.
- Metabolism: Ester local anesthetics are hydrolyzed in the plasma by pseudocholinesterase. Amide local anesthetics are primarily metabolized in the liver.
- Excretion: The kidneys are the primary excretory organ for local anesthetic and its metabolites.
Systemic Actions of Local Anesthetics
- Central Nervous System: Crosses the blood-brain barrier. Low blood levels do not affect CNS, while high blood levels can lead to generalized tonic-clonic convulsions.
- Cardiovascular System: Produces myocardial depression, decreases electrical excitability of the myocardium, decreases the force of contraction, and causes hypotension.
- Respiratory System: Non-overdose levels have a direct relaxant action on bronchial smooth muscles, while overdose levels can lead to respiratory arrest.
Composition of Local Anesthetics Solution
- Local anesthetic drug: For blockade of nerve conduction (lidocaine HCL).
- Sodium Chloride: For isotonicity of the solution preventing cell damage.
- Sterile Water: Provides volume.
- Vasoconstrictor (epinephrine): Increases depth and duration of anesthesia, reduces absorption of local anesthetic and its toxicity.
- Sodium Meta Bisulfite: Antioxidant for vasoconstrictor.
- Methyl Paraben: Bacteriostatic agent.
Clinical Action of Specific Agents
-
Procaine:
- Ester, potency: 1 (procaine = 1), toxicity: 1 (procaine = 1).
- Rapidly hydrolyzed in plasma by plasma pseudocholinesterase.
- Excreted in urine: 2% unchanged, 90% as PABA, 8% as diethylaminoethanol.
- Produces the greatest vasodilation of all local anesthetics.
- Onset of action: 6 to 10 minutes.
- Effective dental concentration: 2% to 4%.
- Anesthetic Half-Life: 0.1 hour (short acting).
- Uses: Immediate management of accidental intraarterial (IA) injection, and breaking arteriospasm.
-
Propoxycaine:
- Not available alone due to high toxicity.
- Combined with procaine for more rapid onset and prolonged anesthesia.
- Maximum recommended dose for adults: 6.6 mg/kg.
-
Lidocaine:
- Amide, potency: 2 (procaine = 1), toxicity: 2 (procaine = 1).
- Metabolized by microsomal fixed-function oxidases in the liver.
- Excreted via the kidneys: less than 10% unchanged, more than 80% as metabolites.
- Less vasodilating than procaine, greater than prilocaine or mepivacaine.
- Effective dental concentration: 2% with epinephrine.
- Onset of action: rapid (3 to 5 minutes).
- Pulpal anesthesia: 60 minutes (intermediate duration).
- Soft tissue anesthesia: 180 -300 minutes (3-5 hours).
- Maximum recommended dose with epinephrine for adults: 7.0 mg/kg.
- Pregnancy classification: B (safe during pregnancy).
- Uses: 2% (plain) - no dental indication; 2% with 1:50,000 epinephrine - hemostasis (green); 2% with 1:100,000 or 1:200,000 - local anesthesia (red).
- Compared to procaine: more rapid onset, more profound anesthesia, longer duration, greater potency.
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Mepivacaine:
- Amide, potency: 2 (procaine = 1), toxicity: 1.5 to 2 (procaine = 1).
- Metabolized in the liver by microsomal fixed-function oxidases.
- Excreted via the kidneys: 1% to 16% unchanged.
- Produces only slight vasodilation.
- Effective dental concentration: 3% (plain) - short duration, 2% with vasoconstrictor - intermediate duration.
- Onset of action: rapid (3 to 5 minutes).
- Pulpal anesthesia: 20-40 minutes for 3%, 60 minutes for 2%.
- Soft tissue anesthesia: 2-3 hours for 3%, 3-5 hours for 2%.
- Maximum recommended dose for adults: 6.6 mg/kg.
- Pregnancy classification: C (not safe).
- Uses: 3% mepivacaine plain (short acting) - pediatric & geriatric patients or when vasoconstrictor is not indicated; 2% mepivacaine with vasoconstrictor (intermediate acting) - levonordeferin (1:20,000) & epinephrine (1:100,000).
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Prilocaine:
- Amide, use: 4% plain (no vasoconstrictor) or 4% with 1:200,000 epinephrine.
- Considered safe as it is rapidly biotransformed.
- Maximum recommended dose: 8mg/kg.
- Contraindications: Idiopathic or congenital methemoglobinemia, hemoglobinopathies (sickle cell anemia), cardiac or respiratory failure.
Key Points to Remember
- Local Anesthetics produce anesthesia by blocking sodium channels at the nerve cell membrane.
- The duration of action of a local anesthetic is dependent on its rate of metabolism and elimination.
- Vasoconstrictors, like epinephrine, are often added to local anesthetic solutions to prolong the duration of anesthesia and reduce the risk of toxicity.
- It is important to always consult a qualified healthcare professional for any questions or concerns you may have regarding local anesthetics and vasoconstrictors.
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Description
Explore the classification of local anesthetics based on their chemical structure, duration of action, and mode of application. This quiz covers examples of both ester and amide types, injectable and topical forms, and delves into the pharmacokinetics of these agents. Test your knowledge on how local anesthetics work and their physiological effects.
