Chapter 3: Pharmacology of Local Anesthetic Agents
Questions
- What is the primary mechanism of action of local anesthetics?
A. Increase potassium efflux
B. Stimulate sodium entry into neurons
C. Block sodium ion channels
D. Inhibit calcium ion release - Which component of the local anesthetic molecule determines its classification as an ester or amide?
A. The aromatic ring
B. The intermediate chain
C. The terminal amine group
D. The protein-binding site - What organ is primarily responsible for the metabolism of amide local anesthetics?
A. Kidneys
B. Liver
C. Lungs
D. Intestines - What is the name of the enzyme that metabolizes ester local anesthetics in the blood?
A. Monoamine oxidase
B. Acetylcholinesterase
C. Pseudocholinesterase
D. Cytochrome P450 - Which local anesthetic is known for its fast onset and moderate duration of action?
A. Bupivacaine
B. Procaine
C. Lidocaine
D. Tetracaine - Which local anesthetic is the most potent among commonly used agents in dentistry?
A. Mepivacaine
B. Articaine
C. Prilocaine
D. Bupivacaine - What factor primarily influences the onset of action of a local anesthetic?
A. Its lipid solubility
B. Its protein binding
C. Its vasodilatory effect
D. Its pKa value - What role does lipid solubility play in the effectiveness of local anesthetics?
A. It enhances renal excretion
B. It slows down nerve conduction
C. It increases penetration through nerve membranes
D. It decreases onset time - Which property of a local anesthetic determines its duration of action?
A. Lipid solubility
B. Protein binding
C. pKa
D. Ionization - What is the maximum recommended dose of lidocaine with epinephrine for a healthy adult patient?
A. 200 mg
B. 300 mg
C. 400 mg
D. 500 mg - What characteristic distinguishes articaine from other amide local anesthetics?
A. It is metabolized entirely in the liver
B. It contains an ester group
C. It cannot be used with epinephrine
D. It has no vasodilatory properties - Which amide local anesthetic has the shortest duration of action?
A. Lidocaine
B. Mepivacaine
C. Bupivacaine
D. Articaine - What is the main excretion pathway for local anesthetic metabolites?
A. Sweat glands
B. Respiratory system
C. Kidneys
D. Salivary glands - Which property of local anesthetics allows them to penetrate lipid-rich nerve membranes?
A. High water solubility
B. High lipid solubility
C. High ionization
D. Low protein binding - Which local anesthetic is most associated with methemoglobinemia in high doses?
A. Articaine
B. Prilocaine
C. Bupivacaine
D. Mepivacaine - What is the typical pKa range for most dental local anesthetics?
A. 2.5–3.5
B. 5.0–5.5
C. 7.0–8.5
D. 9.0–10.5 - What is the significance of a local anesthetic’s pKa being close to physiological pH?
A. Faster onset of action
B. Longer duration of action
C. Greater toxicity
D. Increased protein binding - Which local anesthetic has the highest lipid solubility, contributing to its potency?
A. Lidocaine
B. Prilocaine
C. Articaine
D. Bupivacaine - What term describes the movement of a drug into the bloodstream after administration?
A. Excretion
B. Metabolism
C. Absorption
D. Binding - What is the primary reason vasoconstrictors are added to local anesthetic solutions?
A. To enhance the bitter taste
B. To reduce anesthetic potency
C. To prolong duration and reduce systemic absorption
D. To increase local acidity - Why does a higher pKa value typically result in a slower onset of local anesthetic action?
A. It decreases lipid solubility
B. It increases protein binding
C. It results in fewer base molecules to penetrate the nerve membrane
D. It blocks potassium efflux - How does vasodilation influence the duration of action of a local anesthetic?
A. It prolongs anesthetic retention at the site
B. It accelerates systemic absorption, reducing duration
C. It prevents sodium channel blockage
D. It enhances lipid solubility of the drug - Why is articaine often preferred for infiltration in the maxillary arch?
A. It has poor tissue penetration
B. It is rapidly absorbed systemically
C. It diffuses effectively through bone
D. It has a slower onset compared to other amides - How does protein binding affect the effectiveness of a local anesthetic?
A. It shortens the duration of action
B. It increases metabolism in the liver
C. It enhances binding to nerve membranes, prolonging the effect
D. It decreases the risk of toxicity - What is the significance of lipid solubility in anesthetic potency?
A. Highly lipid-soluble drugs penetrate nerve membranes more easily
B. It increases the water solubility of the agent
C. It ensures quicker hepatic excretion
D. It enhances the bitter taste of the anesthetic - Why is lidocaine considered the standard anesthetic for comparison?
A. It has the longest duration
B. It is the least potent
C. It has balanced potency, onset, and safety
D. It is the most expensive - How does the presence of a vasoconstrictor in an anesthetic solution affect systemic toxicity risk?
A. It increases toxicity by slowing clearance
B. It increases anesthetic concentration
C. It reduces systemic absorption and lowers toxicity risk
D. It blocks sodium channels faster - Why is knowledge of anesthetic metabolism important when treating medically compromised patients?
A. To determine the needle gauge to use
B. To choose agents with minimal liver or kidney involvement
C. To ensure anesthetics are stored correctly
D. To avoid using topical agents - How does pH influence the activity of a local anesthetic in infected tissues?
A. High pH increases drug ionization, enhancing penetration
B. Low pH in infection reduces base form, slowing onset
C. Neutral pH in infection accelerates absorption
D. Acidic pH activates more sodium channels - Why might prilocaine be contraindicated in patients with oxygen transport disorders?
A. It causes excessive vasoconstriction
B. It accelerates sodium influx
C. It can induce methemoglobinemia
D. It is excreted through the lungs - How does inflammation at the injection site affect local anesthetic efficacy?
A. Increases absorption and speeds onset
B. Decreases pH, limiting anesthetic penetration
C. Enhances protein binding, prolonging duration
D. Prevents metabolism in the bloodstream - Why are ester anesthetics more likely to cause allergic reactions than amides?
A. They contain amino acid chains
B. They are stored longer in tissues
C. Their metabolism produces para-aminobenzoic acid (PABA)
D. They are injected in larger volumes - What is the functional role of the terminal amine group in a local anesthetic molecule?
A. Controls metabolism in the liver
B. Enhances sodium channel blocking in its ionized form
C. Determines lipid solubility
D. Reduces protein binding - How does the vasodilatory property of local anesthetics impact their clinical use?
A. It enhances anesthetic potency
B. It promotes prolonged anesthesia
C. It increases systemic absorption and reduces duration
D. It improves lipid solubility - Why is bupivacaine not typically used for routine dental hygiene procedures?
A. It lacks vasodilating activity
B. It has a short duration of action
C. Its onset is too fast for short procedures
D. It has a long duration, not ideal for shorter appointments - How does the use of a vasoconstrictor impact the distribution of a local anesthetic?
A. Increases diffusion through bone
B. Limits blood flow, keeping the drug near the injection site
C. Enhances protein breakdown
D. Stimulates liver metabolism - Why does prilocaine have a lower risk of systemic toxicity in healthy individuals?
A. It is rapidly metabolized in the lungs
B. It is excreted unchanged in the urine
C. It is less lipid-soluble than other agents
D. It is partially metabolized outside the liver - What is a potential consequence of exceeding the maximum recommended dose of a local anesthetic?
A. Decreased anesthetic duration
B. Accelerated healing of tissues
C. Increased risk of central nervous system and cardiovascular toxicity
D. Slower sodium channel binding - Why is it important to understand the concept of ionization in local anesthetic pharmacology?
A. Ionized molecules enhance bone penetration
B. Only non-ionized forms can cross nerve membranes effectively
C. Ionized drugs produce longer anesthesia
D. Ionized forms improve renal clearance - How does pKa affect the balance of ionized and non-ionized forms of a local anesthetic?
A. Lower pKa results in more ionized molecules
B. Higher pKa enhances tissue diffusion
C. pKa determines how much of the drug remains active in inflamed tissues
D. pKa closer to physiological pH increases non-ionized form, speeding onset - A patient with a known liver condition requires local anesthesia. Which anesthetic agent would be most appropriate to minimize hepatic metabolism?
A. Lidocaine
B. Bupivacaine
C. Articaine
D. Mepivacaine - You plan to perform a long periodontal debridement. Which anesthetic would provide the longest duration of action?
A. Lidocaine 2% with epinephrine
B. Mepivacaine 3% plain
C. Bupivacaine 0.5% with epinephrine
D. Prilocaine 4% plain - During infiltration in the maxilla, your patient experiences rapid anesthesia. Which property of the anesthetic likely contributed to this effect?
A. High protein binding
B. High pKa
C. High lipid solubility
D. Low water solubility - A patient is taking medications that inhibit liver enzymes. Which local anesthetic may present increased risk of toxicity in this patient?
A. Lidocaine
B. Articaine
C. Procaine
D. Tetracaine - Your patient has a history of allergic reaction to ester anesthetics. Which of the following is safest to administer?
A. Tetracaine
B. Procaine
C. Lidocaine
D. Benzocaine - After administering prilocaine for an extended procedure, your patient begins to show signs of cyanosis without respiratory distress. What is the likely condition?
A. Allergic reaction
B. Cardiovascular collapse
C. Methemoglobinemia
D. Asthma attack - You are treating a medically compromised patient with heart disease. Which anesthetic strategy best reduces systemic impact?
A. Use maximum dose of lidocaine
B. Use plain mepivacaine without vasoconstrictor
C. Use articaine with 1:50,000 epinephrine
D. Avoid anesthetics and use general anesthesia - While reviewing dosage, you calculate that your patient has received 400 mg of lidocaine. The patient weighs 70 kg. What should you do next?
A. Administer another cartridge immediately
B. Proceed, as this is below the safe maximum
C. Stop administration and monitor for toxicity signs
D. Continue treatment with a different anesthetic - You administer an anesthetic with a high pKa, and the onset is delayed. What adjustment could improve effectiveness?
A. Increase the pKa further
B. Use an anesthetic with pKa closer to 7.4
C. Add more protein-binding sites
D. Use a vasoconstrictor alone - You are preparing to anesthetize an inflamed area for a dental procedure. What strategy would improve anesthetic effectiveness in acidic tissue?
A. Use a higher-pKa anesthetic
B. Avoid using epinephrine
C. Inject into healthy tissue nearby
D. Increase the dose dramatically
Answers and Explanation
- Answer: C. Block sodium ion channels
Explanation: Local anesthetics block voltage-gated sodium channels, preventing depolarization and the propagation of nerve impulses. - Answer: B. The intermediate chain
Explanation: The type of bond in the intermediate chain (ester or amide linkage) determines the classification of the anesthetic. - Answer: B. Liver
Explanation: Amide local anesthetics are primarily metabolized in the liver by hepatic enzymes. - Answer: C. Pseudocholinesterase
Explanation: Ester anesthetics are broken down in the bloodstream by pseudocholinesterase, a plasma enzyme. - Answer: C. Lidocaine
Explanation: Lidocaine is known for its rapid onset and moderate duration, making it one of the most commonly used anesthetics in dental practice. - Answer: D. Bupivacaine
Explanation: Bupivacaine is the most potent and long-lasting of the common local anesthetics used in dentistry. - Answer: D. Its pKa value
Explanation: The pKa of an anesthetic affects the proportion of molecules in the active base form, influencing the onset time. - Answer: C. It increases penetration through nerve membranes
Explanation: Higher lipid solubility allows anesthetic molecules to penetrate the lipid-rich nerve membrane more effectively. - Answer: B. Protein binding
Explanation: Anesthetic agents with high protein-binding capacity bind to nerve membrane proteins longer, increasing the duration of action. - Answer: D. 500 mg
Explanation: The maximum recommended dose of lidocaine with epinephrine for a healthy adult is 500 mg to minimize the risk of toxicity. - Answer: B. It contains an ester group
Explanation: Articaine is unique among amide anesthetics because it contains an ester side chain, allowing partial metabolism in the plasma. - Answer: B. Mepivacaine
Explanation: Mepivacaine has a relatively short duration of action compared to other amides, especially when used without a vasoconstrictor. - Answer: C. Kidneys
Explanation: Local anesthetic metabolites are primarily excreted by the kidneys after hepatic or plasma metabolism. - Answer: B. High lipid solubility
Explanation: Lipid solubility enables anesthetic agents to cross nerve membranes effectively, which are composed of lipid bilayers. - Answer: B. Prilocaine
Explanation: Prilocaine in large doses is associated with the risk of methemoglobinemia, a condition that reduces oxygen delivery to tissues. - Answer: C. 7.0–8.5
Explanation: Most dental anesthetics have a pKa in the range of 7.0 to 8.5, influencing the balance between ionized and non-ionized forms. - Answer: A. Faster onset of action
Explanation: When the pKa of an anesthetic is close to physiological pH (7.4), a greater proportion of the drug remains in its active base form, resulting in quicker onset. - Answer: D. Bupivacaine
Explanation: Bupivacaine has high lipid solubility, contributing to its potency and extended duration of anesthesia. - Answer: C. Absorption
Explanation: Absorption refers to the process of the drug entering the bloodstream from the site of administration. - Answer: C. To prolong duration and reduce systemic absorption
Explanation: Vasoconstrictors reduce blood flow at the injection site, allowing the anesthetic to remain localized longer and minimizing systemic absorption. - Answer: C. It results in fewer base molecules to penetrate the nerve membrane
Explanation: A higher pKa means fewer molecules are in the non-ionized base form needed to cross nerve membranes, leading to slower onset. - Answer: B. It accelerates systemic absorption, reducing duration
Explanation: Vasodilation increases blood flow, which removes the anesthetic from the site more quickly, shortening its duration. - Answer: C. It diffuses effectively through bone
Explanation: Articaine has excellent bone penetration, making it highly effective for infiltrations, especially in the dense bone of the maxilla. - Answer: C. It enhances binding to nerve membranes, prolonging the effect
Explanation: High protein binding allows anesthetics to stay attached to receptor sites longer, extending their duration of action. - Answer: A. Highly lipid-soluble drugs penetrate nerve membranes more easily
Explanation: Lipid solubility allows anesthetics to pass through the lipid-rich nerve sheath, improving potency and effectiveness. - Answer: C. It has balanced potency, onset, and safety
Explanation: Lidocaine is widely used as a benchmark because of its reliable combination of effectiveness, moderate duration, and low toxicity. - Answer: C. It reduces systemic absorption and lowers toxicity risk
Explanation: Vasoconstrictors decrease blood flow at the injection site, reducing the rate at which the anesthetic enters circulation and minimizing toxicity. - Answer: B. To choose agents with minimal liver or kidney involvement
Explanation: Patients with liver or kidney impairment require anesthetics that are metabolized or excreted through alternate pathways to avoid complications. - Answer: B. Low pH in infection reduces base form, slowing onset
Explanation: Infected tissues are more acidic, which favors the ionized form of the anesthetic and slows its ability to penetrate nerve membranes. - Answer: C. It can induce methemoglobinemia
Explanation: Prilocaine can oxidize hemoglobin to methemoglobin, impairing oxygen delivery and posing a risk to patients with blood disorders. - Answer: B. Decreases pH, limiting anesthetic penetration
Explanation: Inflammation lowers tissue pH, which increases ionization of anesthetics, reducing the amount of drug in the active (non-ionized) form that can penetrate nerve membranes. - Answer: C. Their metabolism produces para-aminobenzoic acid (PABA)
Explanation: Ester anesthetics are hydrolyzed into PABA, a compound known to trigger allergic reactions in some individuals. - Answer: B. Enhances sodium channel blocking in its ionized form
Explanation: The terminal amine group enables the molecule to become ionized in physiological conditions, allowing it to bind inside sodium channels and block nerve conduction. - Answer: C. It increases systemic absorption and reduces duration
Explanation: Vasodilation allows quicker uptake into the bloodstream, which can shorten the anesthetic’s effect at the site and increase systemic exposure. - Answer: D. It has a long duration, not ideal for shorter appointments
Explanation: Bupivacaine is long-acting, making it more suitable for lengthy or post-operative pain control rather than brief hygiene procedures. - Answer: B. Limits blood flow, keeping the drug near the injection site
Explanation: Vasoconstrictors reduce blood flow, slowing the dispersal of the anesthetic and prolonging its local effect. - Answer: D. It is partially metabolized outside the liver
Explanation: Prilocaine is metabolized in both the liver and lungs, which distributes the metabolic load and reduces toxicity risk in healthy individuals. - Answer: C. Increased risk of central nervous system and cardiovascular toxicity
Explanation: Exceeding safe doses may lead to systemic toxicity, affecting the CNS and cardiovascular system due to high plasma anesthetic levels. - Answer: B. Only non-ionized forms can cross nerve membranes effectively
Explanation: The non-ionized (base) form is lipophilic and can penetrate nerve membranes; ionized forms remain extracellular and are less effective at blocking conduction. - Answer: D. pKa closer to physiological pH increases non-ionized form, speeding onset
Explanation: A lower pKa or one close to 7.4 results in more non-ionized drug, facilitating faster nerve penetration and quicker onset of anesthesia. - Answer: C. Articaine
Explanation: Articaine is partially metabolized in the plasma due to its ester group, making it safer for patients with compromised liver function. - Answer: C. Bupivacaine 0.5% with epinephrine
Explanation: Bupivacaine has the longest duration among common dental anesthetics, ideal for extended procedures. - Answer: C. High lipid solubility
Explanation: Lipid solubility allows anesthetics to rapidly penetrate nerve membranes, contributing to quicker onset. - Answer: A. Lidocaine
Explanation: Lidocaine is metabolized entirely in the liver, so enzyme inhibitors can slow clearance, increasing toxicity risk. - Answer: C. Lidocaine
Explanation: Lidocaine is an amide and does not produce PABA, making it safe for patients allergic to ester anesthetics. - Answer: C. Methemoglobinemia
Explanation: Prilocaine can cause methemoglobinemia, a condition where hemoglobin cannot carry oxygen effectively, leading to cyanosis. - Answer: B. Use plain mepivacaine without vasoconstrictor
Explanation: For heart disease patients, avoiding vasoconstrictors like epinephrine reduces cardiovascular stress. - Answer: C. Stop administration and monitor for toxicity signs
Explanation: The maximum recommended dose of lidocaine with epinephrine is 500 mg. At 400 mg, close to the limit, it’s safer to pause and observe. - Answer: B. Use an anesthetic with pKa closer to 7.4
Explanation: A lower pKa, closer to physiologic pH, ensures more anesthetic remains in the non-ionized form, improving onset time. - Answer: C. Inject into healthy tissue nearby
Explanation: Inflamed tissue is acidic, reducing anesthetic efficacy. Injecting into adjacent healthy tissue allows better diffusion and effectiveness.