Medical Pharmacology Chapter 13:  Clinical Use: opioid analgesics in pain management

• Analgesia

  • Opioids most effective: severe, constant pain

  • Opioids less effective: sharp, intermittent pain

  • Selection and evaluation of opioids

    • Factors to consider:

      • Route of Administration (oral or parenteral)

      • Maximal efficacy

      • Therapy duration

      • Previous experience

• Management of cancer pain and pain associate with other terminal illnesses:  Principles

  • Adequate treatment

  • Concerns about dependence and tolerance -- secondary consideration

  • Fixed-interval opioid administration: more effective than dosing on demand

    • Slower released dosage forms (new) -- may provide longer and more consistent analgesia levels

  • Addition of stimulants (e.g. amphetamines): enhance opioid analgesic effects

  • Clonidine (α₂ adrenergic receptor agonist): may be useful in pain management

•  Obstetrical labor

  • Minimize fetal/neonatal opioid depression

  • Opioid depression: reversible by naloxone

  • Phenylpiperidine agents (e.g. meperidine): may produce less depression, especially respiratory depression in the newborn compared to morphine

• Renal/Biliary Colic

  • Adequate pain relief: strong agonist opioid required

  • Increased dosages may be necessary to overcome increased pain secondary to increased smooth muscle tone

• Acute Pulmonary Edema

  • IV morphine: relieves dyspnea secondary to pulmonary edema

  • Possible mechanism of action:

    • Reduced awareness of shortness of breath

    • Reduced patient anxiety

    • Reduced preload (decreased vascular venous tone)

    • Reduced afterload (decreased peripheral resistance)

•  Cough

  • Cough suppression occurs at lower doses than for opioid analgesia

  • Reduced usage of opioids for cough suppression: due to newer non-analgesic, non-addictive synthetic agents

• Diarrhea

  • All diarrhea controllable with opioids

  • If diarrhea secondary to infection, treat the infection with appropriate chemotherapy

  • Current antidiarrheals utilize agents selected for the gastrointestinal tract with limited CNS actions

1. Way, W.L., Fields, H.L. and Way, E. L. Opioid Analgesics and Antagonists, in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 496-515.

2. Schuckit, M.A. and Segal D.S., Opioid Drug Abuse and Dependence, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp 2508-2512;

3. Coda, B.A. Opioids, In Clinical Anesthesia, 3rd Edition (Barash, P.G., Cullen, B.F. and Stoelting, R.K.,eds) Lippincott-Ravin Publishers, Philadelphia, New York, 1997, pp 329-358.

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