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Chapter 28

Chapter 28. Opioid (Narcotic) Analgesics, Opioid Antagonists, and Nonopioid Centrally Acting Analgesics. Analgesics and Opioids. Analgesics are drugs that relieve pain without causing loss of consciousness. Opioids are the most effective pain relievers available. Terminology. Opioid

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Chapter 28

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  1. Chapter 28 Opioid (Narcotic) Analgesics, Opioid Antagonists, and Nonopioid Centrally Acting Analgesics

  2. Analgesics and Opioids • Analgesics are drugs that relieve pain without causing loss of consciousness. • Opioids are the most effective pain relievers available.

  3. Terminology • Opioid • A general term defined as any drug, natural or synthetic, that has actions similar to those of morphine • Opiate • Applies only to compounds present in opium

  4. Opioid Receptors • Three main classes of opioid receptors • Mu receptors • Kappa receptors • Delta receptors

  5. Classification of Drugs That Act as Opioid Receptors 5

  6. Morphine • Source • Seedpod of the poppy plant • Overview of pharmacologic actions • Receptors involved • Pain relief • Drowsiness • Mental clouding • Anxiety reduction • Sense of well-being

  7. Morphine • Therapeutic use: relief of pain • Mechanism of analgesic action • Moderate to severe pain • Constant dull pain vs. sharp intermittent pain • Preoperative treatment of anxiety

  8. Morphine • Adverse effects • Respiratory depression • Infants and the elderly are especially sensitive • Onset: • IV 7 min; IM 30 min; subQ up to 90 min, may persist 4–5 hr • 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 (eg, alcohol, barbiturates, benzodiazepines) • Can compromise patients with impaired pulmonary function • Asthma, emphysema, kyphoscoliosis, chronic cor pulmonale, bariatric

  9. Morphine • Adverse effects (cont’d) • Constipation • Orthostatic hypotension • Cough suppression • Biliary colic • Emesis • Urinary retention • Euphoria/dysphoria • Sedation

  10. Morphine • Adverse effects (cont’d) • Miosis • Intracranial pressure (ICP) • Birth defects • Adverse effects from prolonged use

  11. Morphine • Pharmacokinetics • Administered by several routes: PO, IM, IV, subQ, epidural, and intrathecal • Not very lipid-soluble • Does not cross blood-brain barrier easily • Only small fraction of each dose reaches site of analgesic action

  12. Morphine • Tolerance and physical dependence • Tolerance • Increased doses needed to obtain same response • Develops with analgesia, euphoria, sedation, respiratory depression • Cross-tolerance to other opioid agonists • No tolerance to miosis or constipation develops

  13. Morphine • Tolerance and physical dependence • Physical dependence • Abstinence syndrome with abrupt discontinuation • About 10 hours after last dose: • Initial reaction (yawning, rhinorrhea, sweating) • Progresses to: • Violent sneezing, weakness, nausea, vomiting, diarrhea, abdominal cramps, bone and muscle pain, muscle spasm, kicking movements • Lasts 7–10 days if untreated • Withdrawal unpleasant but not lethal, as is possible with CNS depressants

  14. Morphine • Abuse liability • Precautions • Decreased respiratory reserve • Pregnancy • Labor and delivery • Head injury • Other precautions

  15. Morphine • Drug interactions • CNS depressants • Anticholinergic drugs • Hypotensive drugs • Monoamine oxidase inhibitors • Agonist-antagonist opioids • Opioid antagonists • Other interactions

  16. Morphine • Toxicity • Clinical manifestations • Classic triad • Coma • Respiratory depression • Pinpoint pupils • Treatment • Ventilatory support • Antagonist: naloxone (Narcan) • General guidelines • Monitor full vitals before giving • Give on a fixed schedule

  17. Other Strong Opioid Agonists • Fentanyl (Sublimaze, Duragesic, Abstral, Actiq, Fentora, Onsolis) • 100 times the potency of morphine • Five formulations in three routes • Parenteral (Sublimaze) • Surgical anesthesia • Transdermal (Duragesic)- useful for patients with chronic, severe pain and high degree of tolerance • Patch—heat acceleration • Iontophoretic system—needle-free • Transmucosal • Lozenge on a stick (Actiq) • Buccal film (Onsolis) • Buccal tablets (Fentora) • Sublingual tablets (Abstral)

  18. Other Strong Opioid Agonists • Alfentanil and sufentanil • Remifentanil • Meperidine • Short half-life • Interacts adversely with several other drugs • Toxic metabolite accumulation • Methadone • Treatment for pain and opioid addicts

  19. Other Strong Opioid Agonists • Heroin • Used legally in Europe to relieve pain • High abuse liability • Not more effective than other opioids • See Figure 28-2 • Hydromorphone, oxymorphone, and levorphanol • Basic pharmacology • Preparations, dosage, and administration

  20. Fig. 28–2. Biotransformation of heroin into morphine.

  21. Moderate to Strong Opioid Agonists (hydromorphone, oxymorphone) • Similar to morphine in most respects • Produce analgesia, sedation, euphoria • Can cause: • Respiratory depression, constipation, urinary retention, cough suppression, and miosis • Can be reversed with naloxone • Different from morphine • Produce less analgesia and respiratory depression than morphine • Somewhat lower potential for abuse

  22. 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 acetaminophen

  23. Moderate to Strong Opioid Agonists • Oxycodone • Analgesic actions equivalent to those of codeine • Long-acting analgesic • 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

  24. Moderate to Strong Opioid Agonists • Hydrocodone • Most widely prescribed drug in the United States • Combined with aspirin, acetaminophen, or ibuprofen

  25. Agonist-Antagonist Opioids • Pentazocine • Actions and uses • Preparations, dosage, and administration • Nalbuphine • Butorphanol • Buprenorphine • 7-day patch: Butrans • Sublingual film: Suboxone

  26. Clinical Use of Opioids • Pain assessment • Essential component of management • Based on patient’s description • Evaluate: • Pain location, characteristics, and duration; things that improve/worsen pain • Status before drug and 1 hour after

  27. Dosing Guidelines • Assessment of pain • Pain status should be evaluated before opioid administration and about 1 hour after • Dosage determination • Opioid analgesics must be adjusted to accommodate individual variation • Dosing schedule • As a rule, opioids should be administered on a fixed schedule • Avoiding withdrawal

  28. Clinical Use of Opioids • Physical dependence • State in which an abstinence syndrome will occur if the dependence-producing drug is abruptly withdrawn; it is NOT equated with addiction • Abuse • Drug use that is inconsistent with medical or social norms • Addiction • Behavior pattern characterized by continued use of a psychoactive substance despite physical, psychologic, or social harm

  29. Clinical Use of Opioids • Balance the need to provide pain relief with the desire to minimize abuse • Minimize fears about: • Physical dependence • Addiction- there are patients who are at higher risk for abuse, but those taking opioids for severe pain have an extremely low incidence of addiction

  30. Clinical Use of Opioids • Patient-controlled analgesia • PCA devices • Drug selection and dosage regulations • Comparison of PCA with traditional intramuscular therapy- blood levels stay in the therapeutic range, fewer fluctuations • Patient education- instruct patient to push the “button” as soon as their pain starts to return. Reassure them that they can’t overdose.

  31. Fig. 28–3. Fluctuation in opioid blood levels seen with three dosing procedures.

  32. Opioid Antagonists • Drugs that block the effects of opioid agonists • Principal uses: • Treatment of opioid overdose, relief of opioid-induced constipation • Reversal of postoperative opioid effects • Management of opioid addiction

  33. Pure Opioid Antagonists • Naloxone (Narcan) • Other pure opioid antagonists • Methylnaltrexone (Relistor) • Alvimopan (Entereg) • Naltrexone (ReVia, Vivitrol)

  34. Naloxone • Therapeutic uses • Reversal of opioid overdose • Drug of choice with pure opioid agonist overdose • Titrated cautiously with physical dependence • Reversal of postoperative opioid effects • Titrated to achieve adequate ventilation and to maintain pain relief • Reversal of neonatal respiratory depression • Opioids given during labor and delivery may cause respiratory depression in neonate

  35. Other Opioid Antagonists • Methylnaltrexone • Selective opioid antagonist • Treatment of opioid-induced constipation in late-stage disease for patients on constant opioids

  36. Nonopioid Centrally Acting Analgesics • Relieve pain by mechanisms largely or completely unrelated to opioid receptors • Do not cause respiratory depression, physical dependence, or abuse • Not regulated under the Controlled Substances Act

  37. Tramadol • Mechanism of action • Combination of opioid and nonopioid mechanisms • Therapeutic use • Pharmacokinetics • Adverse effects and interactions • Drug interactions • CNS depressants • Abuse liability • Preparations, dosage, and administration • Immediate-release and extended-release

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