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• Cardiovascular Effects:

  • Usually minimal effects (some bradycardia)

  • BP -- in the absence of stress, well maintained;

  • With stress hypotension may occur

    • Hypotensive reaction -- mechanism

      • Peripheral arterial dilation

      • Venous dilation

      • May be due to central vasomotor effects and histamine release

    •  Reduced blood volume:

      • Increased susceptibility to opioid hypotensive effects

  • With respiratory depression (secondary to opioid administration), PCO₂ increases and causes:

    1. Cerebral vasodilation (decrease in cerebral vascular resistance)

    2. Increase in cerebral blood flow

    3. Increase in intracranial pressure

• Gastrointestinal Opioid Effects:

  • Constipation:

    • Mechanism: local enteric mechanisms and CNS effects

    • Stomach:

      • Motility {rhythmic contraction/relaxation} decreases

      • Tone {constant muscle contraction level} increases

      • Gastric acid (HCl) decreases

    • Small Intestinal Effects:

      • Tone: increases; with spasm

      • Nonpropulsive contractile amplitudes decreases

    • Large Intestinal Effects

      • Propulsive peristaltic waves are diminished

      • Tone increased

      • These effects:

        1. Delay fecal passage (constipating)

        2. Promote water reabsorption (constipating)

      • Opioid pharmacological actions in the large intestine are the basis for opioid use in management of diarrhea

• Biliary tract:

  • Opioids: promote biliary smooth muscle constriction possibly resulting in biliary colic

  •  Sphincter of Oddi may constrict:

    • Biliary and pancreatic secretion reflux

    • Elevated plasma lipase/amylase

• Genitourinary tract:

  • Renal Function: depressed

    • Decreased renal plasma flow

    • Bladder and ureteral tone: increased

      • Urinary retention (particularly in postoperative patients)

      • Increased opioid-induced ureteral tone may worsen ureteral colic due to renal calculus

  • Uterus:

    • Prolong labor

• Neuroendocrine:

  • Opioid analgesics promote release of:

    1. Antidiuretic hormone

    2. Prolactin

    3. Somatotropin

  • Opioid analgesics inhibit released of:

    • Luteinizing hormone which is probably a hypothalamic effect

• Other Effects:

  • Flushing, sweating, itching: central effects & histamine early

  • Opioid affecting the immune system by influencing:

    1. Chemotaxis

    2. Antibody production

• Common effect: sedation + analgesia-- therapeutic doses

• Sweating, dizziness, nausea -- common at higher doses; significant respiratory depression less likely than with pure opioid agonists

  • Respiratory depression: reversible by naloxone; agonist antagonists (nalorphine) less likely to be effective in reversing respiratory depression

• Psychotomimetic effects: agonist-antagonists

  • Nightmares

  • Anxiety

  • Hallucinations