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COURSE OF LOCAL ANESTHESIA100% CORRECT
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Time Course of Local Anesthesia
■ Onset of local anesthesia
■ The ability of an anesthetic to penetrate the axon membrane is determined by
three properties:
Before anesthesia can occur, the anesthetic must diffuse from its site of administration to its
sites of action within the axon membrane. Anesthesia is delayed until this movement has
occurred. The ability of an anesthetic to penetrate the axon membrane is determined by three
properties: molecular size, lipid solubility, and degree of ionization at tissue PH.
– Molecular size: small can cross rapidly
– Lipid solubility: high lipid solubility cross rapidly
– Degree of ionization at tissue pH: low ionization cross rapidly
■ Termination of local anesthesia
– Impact of regional blood flow
In areas where blood flow is high, anesthetic is carried away quickly, and effects terminate with
relative haste. In regions where blood flow is low, anesthesia is more prolonged.
Basic Pharmacology of Local Anesthetics
■ Use with vasoconstrictors
– Epinephrine: Decreases local blood flow, delays systemic absorption of
the anesthetic, prolongs anesthesia, and reduces the risk of toxicity
Pharmacology of Local Anesthetics
• Adverse effects
– Absorption of the vasoconstrictor itself can result in systemic toxicity: rate of
absorption is determined largely by blood flow to the site of administration.
■ Palpitations
■ Tachycardia
■ Nervousness
■ Hypertension
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
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– Alpha- and beta-adrenergic antagonists
■ Adverse effects
– Central nervous system: Excitation followed by depression
– Cardiovascular: Bradycardia, heart block, reduced contractile force,
cardiac arrest, and hypotension
– Allergic reactions
– Use in labor and delivery
– Methemoglobinemia
Topical benzocaine can cause methemoglobinemia, a blood disorder in which hemoglobin is
modified such that it cannot release oxygen to tissues. If enough hemoglobin is converted to
methemoglobin, death can result. Methemoglobinemia has been associated with benzocaine
liquids, sprays, and gels.
Lidocaine
■ Most widely used local anesthetic
■ Topical and injectable applications
■ Effects extended if given with epinephrine
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
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■ Also used for cardiac dysrhythmias: suppresses cardiac excitability secondary
to blockade of sodium channels
Allergic reactions are rare with this drug
Other Local Anesthetics
■ Grouped according to route
– Topical: Lidocaine, tetracaine, and cocaine
– Drugs are absorbed through the skin and can cause systemic reactions
– Application guidelines:
■ Apply smallest amount needed
■ Avoid application to large areas
■ Avoid application to broken or irritated skin
■ Avoid strenuous exercise, wrapping the site, and heating the site, all
of which can accelerate absorption by increasing skin temperature
Opioid Receptors
■ Three main classes of opioid receptors
– Mu receptors: Responses to activation of these receptors include:Analgesia,
respiratory depression, euphoria, sedation, and physical dependence. These
are the most important because opioids act primarily by activating mu
receptors
– Kappa receptors: Activation of these receptors can produce: Analgesia
and sedation; kappa activation may underlie psychotomimetic effects
seen with certain opioids
– Delta receptors- generally opioids do not interact with these
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
COURSE OF LOCAL ANESTHESIA100% CORRECT
DOWNLOAD TO SCORE A RATED A+
Classification of Drugs That Act as Opioid Receptors
■ Agonist, partial agonist, or antagonist
– Pure opioid agonists activate mu and kappa
– Agonist-antagonist opioids taken alone produce analgesia but when combined
with pure opioids they antagonize analgesia caused from prue opioid (Talwin
is an example)
– Pure opioid antagonists used purely for reversing the respiratory and
CNS depression caused by overdose with opioid agonists
Pure Opioid Agonists
■ Activate mu receptors and kappa receptors
■ Can produce analgesia, euphoria, sedation, respiratory depression,
physical dependence, constipation, and other effects
■ Morphine: Strong opioid agonists and moderate to strong opioid agonists
■ Codeine: Moderate to strong agonists
COURSE OF LOCAL ANESTHESIA100% CORRECT
DOWNLOAD TO SCORE A RATED A+
Time Course of Local Anesthesia
■ Onset of local anesthesia
■ The ability of an anesthetic to penetrate the axon membrane is determined by
three properties:
Before anesthesia can occur, the anesthetic must diffuse from its site of administration to its
sites of action within the axon membrane. Anesthesia is delayed until this movement has
occurred. The ability of an anesthetic to penetrate the axon membrane is determined by three
properties: molecular size, lipid solubility, and degree of ionization at tissue PH.
– Molecular size: small can cross rapidly
– Lipid solubility: high lipid solubility cross rapidly
– Degree of ionization at tissue pH: low ionization cross rapidly
■ Termination of local anesthesia
– Impact of regional blood flow
In areas where blood flow is high, anesthetic is carried away quickly, and effects terminate with
relative haste. In regions where blood flow is low, anesthesia is more prolonged.
Basic Pharmacology of Local Anesthetics
■ Use with vasoconstrictors
– Epinephrine: Decreases local blood flow, delays systemic absorption of
the anesthetic, prolongs anesthesia, and reduces the risk of toxicity
Pharmacology of Local Anesthetics
• Adverse effects
– Absorption of the vasoconstrictor itself can result in systemic toxicity: rate of
absorption is determined largely by blood flow to the site of administration.
■ Palpitations
■ Tachycardia
■ Nervousness
■ Hypertension
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
COURSE OF LOCAL ANESTHESIA100% CORRECT
DOWNLOAD TO SCORE A RATED A+
– Alpha- and beta-adrenergic antagonists
■ Adverse effects
– Central nervous system: Excitation followed by depression
– Cardiovascular: Bradycardia, heart block, reduced contractile force,
cardiac arrest, and hypotension
– Allergic reactions
– Use in labor and delivery
– Methemoglobinemia
Topical benzocaine can cause methemoglobinemia, a blood disorder in which hemoglobin is
modified such that it cannot release oxygen to tissues. If enough hemoglobin is converted to
methemoglobin, death can result. Methemoglobinemia has been associated with benzocaine
liquids, sprays, and gels.
Lidocaine
■ Most widely used local anesthetic
■ Topical and injectable applications
■ Effects extended if given with epinephrine
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
COURSE OF LOCAL ANESTHESIA100% CORRECT
DOWNLOAD TO SCORE A RATED A+
■ Also used for cardiac dysrhythmias: suppresses cardiac excitability secondary
to blockade of sodium channels
Allergic reactions are rare with this drug
Other Local Anesthetics
■ Grouped according to route
– Topical: Lidocaine, tetracaine, and cocaine
– Drugs are absorbed through the skin and can cause systemic reactions
– Application guidelines:
■ Apply smallest amount needed
■ Avoid application to large areas
■ Avoid application to broken or irritated skin
■ Avoid strenuous exercise, wrapping the site, and heating the site, all
of which can accelerate absorption by increasing skin temperature
Opioid Receptors
■ Three main classes of opioid receptors
– Mu receptors: Responses to activation of these receptors include:Analgesia,
respiratory depression, euphoria, sedation, and physical dependence. These
are the most important because opioids act primarily by activating mu
receptors
– Kappa receptors: Activation of these receptors can produce: Analgesia
and sedation; kappa activation may underlie psychotomimetic effects
seen with certain opioids
– Delta receptors- generally opioids do not interact with these
, RN5344: REVIEW MODULE 3 PHARM-1 TIME
COURSE OF LOCAL ANESTHESIA100% CORRECT
DOWNLOAD TO SCORE A RATED A+
Classification of Drugs That Act as Opioid Receptors
■ Agonist, partial agonist, or antagonist
– Pure opioid agonists activate mu and kappa
– Agonist-antagonist opioids taken alone produce analgesia but when combined
with pure opioids they antagonize analgesia caused from prue opioid (Talwin
is an example)
– Pure opioid antagonists used purely for reversing the respiratory and
CNS depression caused by overdose with opioid agonists
Pure Opioid Agonists
■ Activate mu receptors and kappa receptors
■ Can produce analgesia, euphoria, sedation, respiratory depression,
physical dependence, constipation, and other effects
■ Morphine: Strong opioid agonists and moderate to strong opioid agonists
■ Codeine: Moderate to strong agonists
