NURS 5334 Pharmacology Module 3 Quiz - See Attached Bundle(GRADED 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 it...
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
– 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
■ Also used for cardiac dysrhythmias: suppresses cardiac excitability secondary to blockade of sodium
channels
Allergic reactions are rare with this drug
, 2
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
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
Agonist-Antagonist Opioids
■ Pentazocine, nalbuphine, butorphanol, and buprenorphine
■ When administered alone, produce analgesia
■ If administered with a pure opioid agonist, can antagonize analgesia caused by the pure agonist
Pure Opioid Antagonists
■ Naloxone [Narcan]: Prototype of the pure opioid antagonists
■ Antagonists at mu and kappa receptors
■ Do not produce analgesia or any of the other effects caused by opioid agonists
■ Reversal of respiratory and central nervous system (CNS) depression caused by overdose with opioid
agonists
■ Methylnaltrexone: Used to treat opioid-induced constipation
Morphine cont
■ Therapeutic use: Relief of pain (moderate to severe)
– Relieves pain without affecting other senses (e.g., sight, touch, smell, and hearing)
– No loss of consciousness
– Relieves pain by mimicking the actions of endogenous opioid peptides, primarily at mu receptors
Morphine cont
■ Adverse effects
– Respiratory depression BB Warning
■ Infants and the elderly are especially sensitive
■ Onset:
– Intravenous, 7 minutes; intramuscular, 30 minutes; subcutaneous, up to 90
minutes; may persist 4 to 5 hours
– Spinal injection: Response may be delayed by hours
■ Tolerance to respiratory depression can develop
■ Increased depression with concurrent use of other drugs that have CNS depressant
actions (e.g., alcohol, barbiturates, and benzodiazepines)
■ Can compromise patients with impaired pulmonary function
– Asthma, emphysema, kyphoscoliosis, chronic cor
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