NURS 5334 Pharmacology Module 3 Quiz

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 3 Morphine ■ Source – Seedpod of the poppy plant Morphine cont ■ Overview of pharmacologic actions – Pain relief – euphoria – Drowsiness – Mental clouding – Anxiety reduction – Respiratory depression – Constipation – Urinary retention – Orthostatic hypotension – Emesis – Miosis – Cough suppression – Biliary colic – Tolerance and physical dependence – Histamine relief 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 4 Morphine cont ■ Adverse effects – Constipation ■ Cause: Suppressed propulsive intestinal contractions, intensified nonpropulsive contractions, increased tone of the anal sphincter, and inhibited secretion of fluids into the intestinal lumen ■ Complications of constipation include fecal impaction, bowel perforation, rectal tearing, and hemorrhoids ■ Treatment includes physical activity, increased intake of fiber and fluids, stimulant laxatives, stool softeners, and polyethylene glycol Prescription meds used for OIC: ■ naloxegol (Movantik) ■ methylnaltrexone (Relistor) Morphine cont ■ Abuse liability ■ Precautions – Decreased respiratory reserve: further compromises respiration in patients with impaired pulmonary function. – Pregnancy infants especially sensitive so give with caution – Labor and delivery – Head injury – Other precautions: Liver impairment, hypotension, reduced blood volume, BPH Morphine cont ■ Drug interactions – CNS depressants – Anticholinergic drugs – Hypotensive drugs – Monoamine oxidase inhibitors – Agonist-antagonist opioids – Opioid antagonists Other Strong Opioid Agonists ■ Fentanyl [Duragesic, Abstral, Actiq, Fentora, Onsolis, Lazanda, Subsys] – 100 times the potency of morphine: This drug is for patients opioid tolerant – Formulations given via three routes ■ Parenteral – Surgical anesthesia ■ Transdermal – Patch: Heat acceleration, iontophoretic system:needle free ■ Transmucosal – Lozenger (Actiq), Buccal Film (Onsolis) Buccal Tablet (Fentora) SL tab (Abstral) SL spray (Subsys) 5 Moderate to Strong Opioid Agonists ■ Codeine – Actions and uses ■ 10% converts to morphine in liver ■ Pain and cough suppression – Preparations, dosage, and administration ■ Usually oral (formulated alone or with aspirin or acetaminophen) ■ 30 mg produces same effect as 325 mg of acetaminophen Codeine alone is Schedule II; combination with nonopioid analgesics Schedule III; Cough schedule V Moderate to Strong Opioid Agonists (Cont.) ■ Oxycodone high abuse potential – Analgesic actions equivalent to those of codeine – Long-acting analgesics ■ Immediate-release ■ Controlled-release [OxyContin] – Abuse: Crushes and snorts or injects medication – 2010 OP formulation much harder to crush and does not dissolve into an injectable solution to decrease risk of abuse