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Questions and Answers
What percentage of anesthetic is removed from the bloodstream after the second half-life?
What percentage of anesthetic is removed from the bloodstream after the second half-life?
Which of the following anesthetics is an ester?
Which of the following anesthetics is an ester?
What is the primary organ responsible for metabolizing amide local anesthetics?
What is the primary organ responsible for metabolizing amide local anesthetics?
What component of local anesthetics determines the potency of the anesthetic drug?
What component of local anesthetics determines the potency of the anesthetic drug?
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Which ingredient is commonly added to local anesthetic solutions to prevent the degradation of vasoconstrictors?
Which ingredient is commonly added to local anesthetic solutions to prevent the degradation of vasoconstrictors?
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What is the effect of adding vasoconstrictors to local anesthetic solutions?
What is the effect of adding vasoconstrictors to local anesthetic solutions?
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Which statement is true regarding ester and amide local anesthetics?
Which statement is true regarding ester and amide local anesthetics?
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What is a significant advantage of submucosal injection over topical administration?
What is a significant advantage of submucosal injection over topical administration?
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What type of enzyme hydrolyzes ester local anesthetics in the plasma?
What type of enzyme hydrolyzes ester local anesthetics in the plasma?
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What is the primary reason topical anesthetic agents are prepared in higher concentrations?
What is the primary reason topical anesthetic agents are prepared in higher concentrations?
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What major metabolite is produced from the metabolism of Articaine?
What major metabolite is produced from the metabolism of Articaine?
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Why are vasoconstrictors beneficial when added to local anesthetic solutions?
Why are vasoconstrictors beneficial when added to local anesthetic solutions?
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How do synthetic local anesthetics usually exist during manufacturing?
How do synthetic local anesthetics usually exist during manufacturing?
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What role does the hydrophilic terminal amine play in local anesthetics?
What role does the hydrophilic terminal amine play in local anesthetics?
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What is a primary disadvantage of using topical anesthetics?
What is a primary disadvantage of using topical anesthetics?
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Which component influences whether a local anesthetic is classified as an ester or an amide?
Which component influences whether a local anesthetic is classified as an ester or an amide?
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What is the primary use of sodium hydroxide in a solution?
What is the primary use of sodium hydroxide in a solution?
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Which local anesthetic is known for producing the greatest vasodilating properties?
Which local anesthetic is known for producing the greatest vasodilating properties?
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What is the typical concentration of benzocaine used in dentistry?
What is the typical concentration of benzocaine used in dentistry?
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What is the duration of action for tetracaine after topical application?
What is the duration of action for tetracaine after topical application?
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Which local anesthetic is known for having anticonvulsant properties?
Which local anesthetic is known for having anticonvulsant properties?
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What characteristic makes articaine different from other amide anesthetics?
What characteristic makes articaine different from other amide anesthetics?
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In what scenario would mepivacaine be considered a good alternative?
In what scenario would mepivacaine be considered a good alternative?
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How does prilocaine compare in toxicity to other local anesthetics?
How does prilocaine compare in toxicity to other local anesthetics?
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What is the expected effect of a local anesthetic with a higher pKa value on its onset of action?
What is the expected effect of a local anesthetic with a higher pKa value on its onset of action?
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Which local anesthetic has the lowest pKa and is an exception among others?
Which local anesthetic has the lowest pKa and is an exception among others?
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In inflamed or infected tissues, why is adequate nerve blockade more challenging?
In inflamed or infected tissues, why is adequate nerve blockade more challenging?
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Which group of local anesthetics contains the agent Procaine?
Which group of local anesthetics contains the agent Procaine?
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What happens to the number of free base molecules when an anesthetic is injected into tissue with a pH lower than 7.4?
What happens to the number of free base molecules when an anesthetic is injected into tissue with a pH lower than 7.4?
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What is the primary difference between esters and amides in local anesthetics?
What is the primary difference between esters and amides in local anesthetics?
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Which local anesthetic has the highest pKa in the provided examples?
Which local anesthetic has the highest pKa in the provided examples?
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What does the elimination half-life of a local anesthetic refer to?
What does the elimination half-life of a local anesthetic refer to?
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Study Notes
Key Components of Local Anesthetics
- All local anesthetics are composed of three main parts: a lipophilic aromatic ring, an intermediate chain, and a hydrophilic terminal amine.
- The lipophilic ring determines the anesthetic's potency, with higher lipid solubility leading to greater potency.
- The intermediate chain dictates whether the anesthetic is an ester or an amide, affecting its breakdown. Esters are hydrolyzed by esterases, while amides are broken down by liver enzymes.
- The hydrophilic amine is the active form that binds to nerve membrane receptors.
Routes of Delivery
- Local anesthetics can be administered topically or through submucosal injection.
- Topical application involves applying the drug to mucosal surfaces for localized pain relief. It uses higher concentrations than injectable forms for better diffusion.
- Submucosal injection is more effective due to direct administration near the targeted nerve tract.
Pharmacodynamics of Local Anesthetics
- Pharmacodynamics studies the effects of drugs on the body, focusing on mechanisms of action and dose-response relationships.
- Local anesthetics are weak bases and are manufactured as water-soluble salts (hydrochlorides) for injection.
The Role of pH
- Ideal pKa for an anesthetic is 7.4, balancing charged and uncharged molecules for optimal diffusion through nerve membranes.
- Most local anesthetics have pKa values above 7.5, with a pH around 5-6 in plain solutions and lower with vasoconstrictors, leading to a predominantly charged form in tissue.
- Higher pKa values result in fewer uncharged molecules, slowing diffusion and onset of action.
Infection and Anesthesia
- Inflammation or infection weakens anesthetic effectiveness due to reduced penetration through the nerve sheath and increased absorption into dilated blood vessels.
- The acidic environment in infections lowers tissue pH, further reducing uncharged molecules and hindering anesthetic efficacy.
- Anesthetics with lower pKa values, like mepivacaine (pKa 7.7), are preferred in these cases.
Classification of Local Anesthetics
- Local anesthetics are chemically classified into esters and amides.
- Esters include procaine, tetracaine, benzocaine, and chloroprocaine.
- Amides include lidocaine, mepivacaine, bupivacaine, prilocaine, and articaine.
Metabolism of Local Anesthetics
- The elimination half-life represents the time taken for 50% of the drug to be metabolized.
- Ester local anesthetics are hydrolyzed in plasma and liver by esterases, and are no longer commonly used due to allergy risks.
- Amide local anesthetics are primarily metabolized in the liver, with a more complex process than esters.
- Articaine, an amide, is rapidly metabolized in blood by plasma cholinesterase.
Composition of Local Anesthetic Solutions
- Local anesthetic solutions often contain vasoconstrictors (epinephrine, levonordefrin) to prolong duration and reduce systemic toxicity.
- Vasoconstrictor preservatives (bisulfites) are added to stabilize vasoconstrictors, but also increase acidity, which affects anesthetic diffusion.
- Sodium hydroxide is a buffer that adjusts solution pH, while sodium chloride creates an isotonic solution for injection.
Ester-Type Local Anesthetics
Procaine HCl
- Procaine (Novocain) was the first synthetic anesthetic used in dentistry.
- It has strong vasodilating properties and lacks pulpal anesthesia effectiveness.
Benzocaine
- A common topical anesthetic available in various formulations.
- Commonly used at 20% concentration in dentistry.
Tetracaine
- Long-acting ester anesthetic for injection or topical use.
- Slow onset and duration of action is approximately 45 minutes topically.
Amid-Type Local Anesthetics
Lidocaine
- The first amide anesthetic suitable for nerve blocks in dentistry.
- Has anticonvulsant properties at levels below those causing toxicity.
- May cause initial sedation compared to other anesthetics.
Mepivacaine HCl
- Similar to lidocaine, but a xylidine derivative.
- Available in plain and levonordefrin formulations, offering an alternative when vasoconstrictors are contraindicated.
Prilocaine HCl
- A toluidine derivative, less toxic than lidocaine, mepivacaine, and articaine.
Articaine
- Derived from thiophene, unlike other amides, resulting in better lipid solubility and diffusion.
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Description
Explore the fundamental parts of local anesthetics, including their structure and potency. Learn about the differences between esters and amides and their respective breakdown processes. Discover the various routes of delivery for effective pain relief.
