Opioid Adverse Effects – Mnemonic

Mnemonic: MORPHINES

opioid receptors

1. Miosis

  • Mechanism: Stimulation of Edinger-Westphal nucleus of Cranial nerve III

2. Orthostatic hypotension

  • Mechanism: Vasodilation due to –
    • Direct action decreasing tone of blood vessels
    • Histamine release
    • Depression of vasomotor center

3. Respiratory depression

  • Mechanism: Inhibits respiratory center in a dose-dependent manner (neurogenic, hypercapneic and hypoxic drives in succession)

4. Physical/Psychological dependence and tolerance

  • Mechanisms of tolerance:
    • Pharmacodynamic (cellular tolerance) > Pharmacokinetic (enhanced rate of metabolism)
    • Constipating and Miotic actions do not exhibit tolerance
  • Mechanism of dependence: Mu receptor mediated

5. Histamine release

  • Mechanism: Displacement (not degranulation) of histamine from mast cell granules

6. Increased ICP

  • Mechanism: Increase in arterial carbon-dioxide tension

7. Nausea

  • Mechanism: Sensitizes CTZ center to vestibular and other impulses

8. Euphoria

  • Mechanism: DA release in nucleus accumbance

9. Sedation

  • Mechanism: Stimulates mu receptors

10. Smooth muscle contraction

  • Constipation: Increased tone of intestine; Spasm of sphincters and Decrease in GI secretions
  • Biliary colic: Spasm of sphincter of Oddi
  • Urinary urgency and difficulty in micturition: Increased tone of both detrusor and sphincter
  • Bronchoconstriction: Histamine release

11. Serotonin syndrome (Tramadol)

  • Mechanism: Inhibits reuptake of NA and 5-HT (also the mechanism for activation of monoaminergic spinal inhibition of pain)


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