Local Anesthetics: Types and Uses
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Questions and Answers

Which of the following correctly describes the mechanism of action of local anesthetics?

  • They act by increasing the influx of calcium ions.
  • They prevent sodium entry by blocking sodium channels in the axonal membrane. (correct)
  • They induce structural damage to neurons.
  • They block nerve conduction by inhibiting potassium channels.

Ester-type local anesthetics are metabolized in the liver.

False (B)

What are the two main classes of local anesthetics?

Esters and amides

Local anesthetics lead to a reversible loss of sensation in a restricted area without causing loss of __________.

<p>consciousness</p> Signup and view all the answers

What is the primary factor that influences the absorption of local anesthetics into the bloodstream?

<p>The route of administration (D)</p> Signup and view all the answers

Match the following local anesthetics with their respective classes:

<p>Benzocaine = Ester Bupivacaine = Amide Lidocaine = Amide Procaine = Ester</p> Signup and view all the answers

The duration of action for Bupivacaine is higher compared to Lidocaine due to its protein binding capacity.

<p>True (A)</p> Signup and view all the answers

What factors can influence the entry of local anesthetics into the circulation?

<p>Vasodilating ability of the drug, volume and concentration, vascularity of tissues, route of administration, presence of vasoconstrictor</p> Signup and view all the answers

Which anesthetic agent is known for causing intense vasoconstriction?

<p>Cocaine (A)</p> Signup and view all the answers

Procaine is effective when administered topically.

<p>False (B)</p> Signup and view all the answers

What is the primary metabolite of ester type local anesthetics?

<p>Para-aminobenzoic acid (PABA)</p> Signup and view all the answers

Lignocaine can be administered in various formulations, including cream, ointment, and ______.

<p>jelly</p> Signup and view all the answers

Match the following anesthetic agents with their characteristics:

<p>Lignocaine = Short duration of action Procaine = Preferred injectable local anesthetic for many years Bupivacaine = Long-acting local anesthetic Benzocaine = Used mainly as topical agent</p> Signup and view all the answers

What is the maximum dosage of topical cocaine?

<p>100 mg (A)</p> Signup and view all the answers

All ester-type drugs are metabolized in the liver.

<p>False (B)</p> Signup and view all the answers

What serious side effect can topical benzocaine cause, especially in children?

<p>Methemoglobinemia</p> Signup and view all the answers

The half-life of procaine is ______ minutes.

<p>2</p> Signup and view all the answers

Match the anesthetic agent with its half-life:

<p>Lignocaine = 90 minutes Procaine = 2 minutes Bupivacaine = 160 minutes Mepivacaine = 120 minutes</p> Signup and view all the answers

Which local anesthetic has the longest duration of action?

<p>Bupivacaine (A)</p> Signup and view all the answers

Lignocaine is less toxic than procaine.

<p>True (A)</p> Signup and view all the answers

In which specific medical scenario is procaine still indicated for use?

<p>In patients with proven allergy to the amide group</p> Signup and view all the answers

Mepivacaine is indicated for use when a local anesthetic without ______ is needed.

<p>vasoconstrictor</p> Signup and view all the answers

What is the onset time of prilocaine?

<p>4 minutes</p> Signup and view all the answers

What should be done to the normal local anaesthetic dose in a patient with impaired liver function?

<p>Reduce the dose (D)</p> Signup and view all the answers

Cocaine is primarily a CNS depressant with minimal effects at safe clinical doses.

<p>False (B)</p> Signup and view all the answers

What type of allergic reactions can be triggered by local anesthetics?

<p>Hypersensitivity reactions</p> Signup and view all the answers

Local anesthetics can cross the placenta, causing ______ and CNS ______ in the neonate.

<p>bradycardia, depression</p> Signup and view all the answers

Match the adverse effects with their description:

<p>CNS effects = Light-headedness and dizziness Cardiovascular toxicity = Bradycardia and arrhythmias Local tissue toxicity = Delayed wound healing Bupivacaine irritancy = Highest local tissue irritancy</p> Signup and view all the answers

Which of the following cardiovascular effects can local anesthetics cause at high doses?

<p>Cardiac arrest (B)</p> Signup and view all the answers

All patients allergic to one ester-type anesthetic will be allergic to all ester-type agents.

<p>True (A)</p> Signup and view all the answers

What medication can be used to prevent or treat CNS effects of local anesthetics?

<p>Diazepam or midazolam</p> Signup and view all the answers

Local anesthetics relax vascular smooth muscle causing ______.

<p>vasodilation</p> Signup and view all the answers

Which local anesthetic is noted for having the highest local tissue irritancy?

<p>Bupivacaine (B)</p> Signup and view all the answers

Flashcards

What are Local Anesthetics?

Drugs that cause reversible loss of sensation, particularly pain, in a localized area of the body, without causing structural damage to nerves.

How are local anesthetics classified?

Local anesthetics are categorized into two main groups based on their chemical structure: esters and amides.

How do local anesthetics work?

Local anesthetics work by blocking sodium channels in the nerve cell membrane. This prevents sodium ions from entering the cell and stops the nerve impulse from traveling.

What determines the duration of a local anesthetic?

The duration of action for local anesthetics is influenced by factors like protein binding. Drugs that bind strongly to proteins stay in the body for longer, leading to a longer anesthetic effect.

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How are local anesthetics absorbed?

Local anesthetics are absorbed into the bloodstream and distributed throughout the body. The rate of absorption varies depending on blood flow to the site of administration and other factors.

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How are local anesthetics metabolized?

Ester-type local anesthetics are broken down by enzymes in the blood called esterases. Amide-type anesthetics are metabolized by enzymes in the liver.

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How does pH influence local anesthetics?

Increased acidity at the site of administration can increase the effectiveness of some local anesthetics.

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How do concentration and volume affect local anesthetics?

The amount of local anesthetic used and its concentration affect how quickly the anesthetic takes effect and how long it lasts.

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Ester type local anesthetics

A group of local anesthetics that are metabolized in the plasma by pseudocholinesterase enzyme, primarily in the liver. This enzyme plays a vital role in their breakdown.

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Cocaine

The first and most potent local anesthetic agent, but it's rarely used due to its potential for misuse. It's an excellent topical anesthetic.

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Procaine

A classic local anesthetic, but its use has decreased with newer agents. It's a good choice for patients allergic to amides.

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Benzocaine

A topical anesthetic, used in high concentrations due to its low toxicity. However, be cautious with young children.

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Para-aminobenzoic acid (PABA)

The major metabolite of ester-type local anesthetics. It's responsible for allergic reactions.

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Amide type local anesthetics

A group of local anesthetics that are metabolized in the liver, except for Prilocaine. They are generally safer than esters.

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Lidocaine (Xylocaine)

A commonly used amide-type local anesthetic. It can be administered topically or by injection.

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Prilocaine

A potent local anesthetic, less toxic than lidocaine. Its metabolite can cause methemoglobinemia in high doses.

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Bupivacaine

A long-acting local anesthetic, effective for oral surgery. Its duration and onset are longer than many other amide-type anesthetics.

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Etidocaine

A long-acting local anesthetic similar to bupivacaine, but with a faster onset.

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Amide-type local anesthetic metabolites

A byproduct of amide-type local anesthetic metabolism, some of which have sedative properties.

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Epinephrine

Used to delay the absorption of local anesthetics, prolonging their effects.

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Lipophilicity

This property allows local anesthetics to cross cell membranes effectively.

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Half-life

This property relates to how long a drug stays in the body before being broken down.

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Methemoglobinemia

A condition caused by certain anesthetics, particularly prilocaine (in larger doses). It results in a lack of oxygen delivery in the blood.

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CNS Effects of Local Anesthetics

Local anesthetics (LAs) can produce a range of central nervous system (CNS) effects, including euphoria, excitement, mental confusion, restlessness, tremors, muscle twitching, convulsions, unconsciousness, respiratory depression, and even death. These effects are primarily dose-dependent, with higher doses increasing the risk of adverse reactions.

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Cardiovascular Effects of Local Anesthetics

LAs can suppress heart muscle excitability, leading to bradycardia (slow heart rate), heart block (disrupted electrical conduction), reduced heart pumping strength, and even cardiac arrest. These effects become more pronounced at higher doses.

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Allergic Reactions to Local Anesthetics

LAs can trigger various allergic reactions, ranging from mild skin rash to severe anaphylaxis. While patients allergic to one ester-type anesthetic are likely to be allergic to others, cross-allergy between esters and amides is rare, allowing for safe alternatives in case of allergies.

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Blood Vessel Effects of Local Anesthetics

LAs relax blood vessel muscles, leading to vasodilation (widening of blood vessels) and potentially causing low blood pressure (hypotension). However, the cardiac depressant effect of lidocaine is used to treat irregular heartbeats.

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Local Anesthetics and Pregnancy

LAs can cross the placenta (the barrier between mother and fetus) and reach the developing baby, potentially causing bradycardia and CNS depression in the newborn.

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Adverse Effects of Local Anesthetics

Local anaesthetics (LAs) can cause a range of adverse effects, from mild dizziness and lightheadedness to severe convulsions, respiratory arrest, and cardiovascular problems.

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Adverse Effects of Local Anesthetics

LAs can cause a range of adverse effects, from mild dizziness and lightheadedness to severe convulsions, respiratory arrest, and cardiovascular problems.

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Local Anesthetics and Elderly Patients

A reduced dose of LA is often recommended for older patients due to their generally diminished liver function.

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Vasoconstrictors and Local Anesthetics

The use of vasoconstrictors (like epinephrine) with LAs can increase local tissue damage.

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Local Anesthetics and Labor

Local anesthetics can suppress uterine contractions, potentially prolonging labor.

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Study Notes

Local Anesthetics: Classification, Action, and Effects

  • Definition: Local anesthetics (LAs) are drugs that reversibly block sensory perception, primarily pain, in a specific body area. They achieve this by inhibiting nerve impulse generation and conduction without causing damage.

Classification

  • Two main types: Esters and amides.
    • Esters: Contain an ester linkage in their structure.
    • Amides: Contain an amide linkage.

Examples of Ester LAs

  • Benzocaine: Primarily topical use.
  • Procaine: Injectable; rarely used nowadays.
  • Proparacaine: Topical use.

Examples of Amide LAs

  • Bupivacaine: Long-acting, often used in surgery.
  • Lidocaine/Lignocaine: Widely used, topical and injectable.
  • Levobupivacaine: Related to bupivacaine.
  • Mepivacaine: Less vasodilating and a shorter duration than lidocaine.
  • Prilocaine: Potent, less vasodilating than lidocaine.
  • Etidocaine: Long-acting, similar to bupivacaine but with faster onset.

Mechanism of Action

  • Sodium Channel Blockade: LAs block nerve conduction by preventing sodium ions (Na+) from entering the axonal membrane during action potential generation. This inhibits the upstroke of the action potential, slowing and eventually blocking conduction.

Absorption

  • Factors Influencing Absorption: Blood flow, drug concentration, the volume of injected LA, vascularity of tissues, route of administartion, and the presence of vasoconstrictors.
  • Vasodilation: The drug's vasodilating ability affects absorption rates.

Pharmacokinetics

  • Onset: Rapid, typically within 5 minutes.
  • Duration: Varies by drug, generally 1-1.5 hours, but impacted by protein binding. Bupivacaine has higher protein binding than lidocaine.
  • pH Dependency: Increased effectiveness in acidic pH.

Metabolism

  • Ester LAs: Metabolized by plasma esterases.
  • Amide LAs: Primarily metabolized in the liver.
  • Metabolism Outcomes: Inactivation of the LA.

Ester Type Drugs: Specific Details

  • Cocaine: Highly potent but rarely used due to abuse potential, and topical use for ear, nose, and throat procedures. Causes intense vasoconstriction.
  • Procaine (Novocaine): Historically used, now less common. Injectable, not effective topically; rapid metabolism due to plasma esterases.
  • Benzocaine: Predominantly topical; rapidly hydrolyzed to low toxicity metabolites. Caution with use in children due to methemoglobinemia risk.

Amide Type Drugs: Specific Details

  • Lidocaine: Rapid, intense, and prolonged anesthetic effect. Highly lipophilic; metabolized only in the liver. High plasma concentrations can lead to CNS and cardiovascular toxicity.
  • Prilocaine: Less vasodilating than lidocaine, high clearance rate; metabolite o-toluidine can cause methemoglobinemia.
  • Mepivacaine: Least vasodilating, metabolized in the liver, suitable when vasoconstriction is not required.
  • Bupivacaine: Long-acting, used in oral surgical procedures; primarily metabolized in the liver.
  • Etidocaine: Long-acting, rapid onset, similar to bupivacaine but potentially more harmful at higher doses, metabolized in the liver.

Systemic Effects

  • Central Nervous System (CNS): Low doses produce minimal CNS effects. Higher doses can induce stimulation followed by depression, leading to seizures, unconsciousness, and death. Includes mild to severe neurological symptoms.
  • Cardiovascular System: Cardiac depression; potential for bradycardia, heart block, reduced contractile force, and arrest at higher doses.
  • Allergic Reactions: Esters frequently increase allergic/hypersensitivity reactions (ranging from mild dermatitis to severe anaphylaxis). Amides are generally less allergenic than esters and thus a better alternative.

Other Key Considerations

  • Blood Vessels: Vasodilation can cause hypotension; vasoconstrictors (like epinephrine) can be added to decrease LA absorption, increasing the duration of action.
  • Labor and Delivery: Local anesthetics can depress uterine contractions and potentially harm the fetus.
  • Adverse Effects: Potential CNS and cardiovascular toxicity as a major adverse effect of local anesthetics.
  • Local Tissue Toxicity: Rare but possible, potentially delayed wound healing and in some cases necrosis.
  • Dose Modifications: Liver impairment and old age reduce metabolism rates; require lower doses of LA.
  • Drug Interactions: Some LAs may interact with other drugs increasing their effects and vice versa.

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Description

This quiz explores the classification, action, and effects of local anesthetics, focusing on their two main types: esters and amides. Through various examples such as benzocaine and bupivacaine, you'll learn how these drugs work and their applications in medical practice.

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