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Understanding Opioid Analgesics: Pharmacology, Effects, and Clinical Uses - A Comprehensive Guide

Explore the classification, mechanisms of action, effects, and clinical applications of opioid and synthetic analgesics for pain management. Learn about opioid receptors, central nervous system impact, cardiovascular effects, and potential adverse reactions. Dive into the uses, cautions, and contraindications of opioid analgesics.

danielmitchell
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Understanding Opioid Analgesics: Pharmacology, Effects, and Clinical Uses - A Comprehensive Guide

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  1. Part 12Analgesics • Opioid analgesics • Synthetic opioid analgesics • Other analgesics

  2. General Considerations • Pain (疼痛)： • 躯体痛－快痛，慢痛 • 内脏痛 • 情绪反应 • Analgesia (镇痛)： • 选择性抑制疼痛感觉， • 不影响意识和其他感觉

  3. Pain Classification An adverse or unpleasant reaction plus the reactions evoked by it Pain Headache (migraine) Acute Chronic Injury Postoperative Flare Neuropathic Mixed Nociceptive Visceral Diabetic neuropathy (DN) Post-herpetic neuralgia(PHN) Radiculopathy(RADIC) Cancer pain Low back pain Osteoarthritis Rheumatoid arthritis Fibromyalgia IBS Pancreatitis Bladder pain Noncardiac chest pain Abdominal pain syndrome

  4. Pain generation and reactions

  5. Stimulation and depolarization of sensory nerve endings

  6. Pain:peripheral sensory reflex

  7. Peripheral mechanisms of pain

  8. Peripheral mechanisms of pain

  9. Primary & secondary hyperalgesia

  10. The perception of somatic pain

  11. The perception and conduction of somatic pain

  12. Conduction pathways of pain

  13. Cortical locations of pain

  14. The fMRI imaging of pain

  15. General Considerations • Classification of analgesics： • Opioid analgesics (centrally acting) • opiates • synthetic agents • Antipyretic, analgesic, and anti-inflammatory drugs (peripherally acting) • aspirin, indomethacin • Other drugs (for special types of pain) • carbamazepine, atropine, nitroglycerin, etc.

  16. A.Opioid Analgesics Morphine 吗啡 Morphine 吗 啡 Heroin 海洛因

  17. Opium

  18. Morphine: • Morphus,the Greek god of dreams

  19. A.Opioid Analgesics • 1. Pharmacological effects • (1) Mechanisms of actions • Acting on central opioid receptors •  receptors •  receptors • δ receptors

  20. Gi Gi AC Opioid Receptors and Endogenous Ligands Enkephalin Endorphin Dynorphin  δ  K+ a g b ATP cAMP g = a b

  21. Mechanisms of morphine actions

  22. Peripheral mechanisms of morphine actions

  23. Central mechanisms of morphine actions: Pain inhibitory system

  24. A.Opioid Analgesics • (2) Central nervous system effects • A. Analgesia：maximal analgesic efficacy； • relieving unpleasant sensation; • euphonia (欣快)and potential of dependence • B. Depression of respiration: • reducing the sensitivity of respiratory center to CO2 • C. Depression of cough reflex • D. Other central effects: miosis, emesis

  25. A.Opioid Analgesics • (3) Cardiovascular effects • A. Postural hypotension： • Releasing histamine; depressing CVS centers • B. Increase of intracranial pressures： • Respiratory depression  brain CO2 increase •  vasodilatation in the brain

  26. A.Opioid Analgesics • (4) Effects on smooth muscles • A. GI tract： • Contispation: increasing resting tone of smooth muscles and sphincters, decreasing propulsive peristalsis and secretions; • Biliary tract：Oddi’s sphincter contraction, increasing the pressure in the biliary tract • B. Respiratory tract：bronchoconstriction • C. Urinary tract：increasing vesical sphincter tone  urinary retention • D. Uterus

  27. A.Opioid Analgesics • (5) Other effects • A. Immune depression • B. Endocrine effects

  28. A.Opioid Analgesics • 2. Clinical uses • (1) Analgesia • the pain of high intensity and the pain of terminal illness • Cautions: • a) obscure the symptoms and the progress of the disease; • b) dependence or addiction; • c) biliary colic: combined with atropine • d) not used for long-term if no clear indications

  29. A.Opioid Analgesics • (2) Cardiac asthma (acute left ventricular failure) • As an adjuvant treatment • A. Vasodilatation: afterload  • B. Sedation: anxiety  • C. Respiratory depression: breathing slowly and deeply • (3) Diarrhea • Mixture containing opiate

  30. A.Opioid Analgesics • 3. Adverse effects • (1) Side effects • (2) Tolerance and dependence • psychological and physic dependence: addiction • withdrawal syndromes or abstinance syndromes

  31. A.Opioid Analgesics • (3) Acute intoxication • coma, respiratory depression, • hypotension, pinpoint pupils • reversed by naloxone, an opioid receptor antagonist • (4) Contraindications • labor and lactation; • bronchial asthma and cor pulmonal; • increased intracranial pressures; • severe hepatic damage

  32. Morphine toxicity can be reversed by opioid receptor antagonist (naloxone)

  33. A.Opioid Analgesics Codeine 可待因 • Analgesia; central antitussive

  34. B.Synthetic Analgesics Pethidine 哌替啶 Dolantin 度冷丁

  35. Structures of natural opioid (morphine) and synthetic analgesics (pethidine) 哌啶环中的叔氮 与叔氮相隔两个碳原子的季碳 与季碳相连的苯环 Morphine Pethidine

  36. B.Synthetic Analgesics • Pethidine • 1. Pharmacological effects • Similar to morphine but ineffective for cough and diarrhea, and its metabolite normeperidine has central stimulant effects. • 2. Clinical uses • analgesia; • cardiac asthma; • preanesthetic medication or artificial hibernation; • 3. Adverse effects • similar to morphine, convulsion (overdose)

  37. B.Synthetic Analgesics • Fentanyl （芬太尼） • high efficacy • combined with droperidol: neuroleptanalgesia • Methadone （美沙酮） • orally effective • long-acting • also used for displacement in heroin or morphine detoxication

  38. B.Synthetic Analgesics • Pentazocine （喷他佐辛, 镇痛新） • receptor agonist /  receptor partial agonist; • low-narcotic analgesic drug • psychotomimetic effects: anxiety, nightmare, hallucinations • Tramadol （曲马朵） • Relatively weak efficacy and dependence

  39. Summary of opioid receptor ligands

  40. 附： 阿片受体拮抗药 Opioid receptor antagonists • Naloxone （纳洛酮） • Naltrexone （纳曲酮） • Antidotes for acute intoxication of opioids • Treatment of shock and other diseases

  41. Summary of opioid receptor ligands

  42. C.Other Analgesics • Rotundine （l-tetrahydropalmatine,罗通定） • dl-Tetrahydropalmatine （延胡索乙素） • chronic pain • sedative effects • no addiction

  43. 附：癌痛的镇痛治疗 • WHO提出的目标： • 2000年，使癌症病人不痛！

  44. 附：癌痛的镇痛治疗 • 三级镇痛阶梯治疗： • 轻度：解热抗炎镇痛药 • 中度：加用或改用弱阿片药,辅助治疗药 • 重度：强阿片药，加非阿片及辅助治疗药 • 应用原则： • 尽可能口服用药 • 按时规则用药，剂量个体化 • 辅助措施

  45. WHO Analgesic Ladder

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