Pharm 101: Oxycodone

Class

Opioid analgesic


Pharmacodynamics
  • Moderate opioid agonist that acts mainly on mu receptors in brain and spinal cord, but also outside of CNS

Pharmacokinetics
  • PO administration, IR/SR formulations
  • Good oral absorption
  • High Vd
  • Low first pass metabolism (compared with morphine)
  • Duration of action 3-4 hours, longer if controlled released formulation
  • Hepatic metabolism by P450 to oxymorphone and noroxycodone
  • Renal excretion of metabolites

Clinical uses
  • Treatment of moderate to severe pain
  • 10 mg morphine = 4.5 mg oxycodone

Adverse effects with acute use of opioid analgesics
  • Respiratory depression
    • Due to inhibition of brainstem respiratory controls allowing less response to hypercapnea
  • CNS:
    • Nausea/vomiting
    • Sedation
    • Dysphoria
    • Delirium
    • Seizures
  • CVS:
    • Bradycardia
    • Hypotension
  • GIT:
    • Urinary retention
    • Constipation
    • Biliary colic
  • Skin:
    • Urticaria
    • Pruritus

Adverse effects with chronic use of opioid analgesics
  • Endocrine:
    • Hypogonadism
    • Immunosuppression
    • Increased feeding
    • Increased GH secretion
  • CNS:
    • Withdrawal effects
    • Dependence*, tolerance**, abuse, addiction
    • Hyperalgesia

Strategies to reduce development of dependence include:

  • Smaller doses at longer intervals
  • Multi-modal analgesia with non-opioid analgesics
  • Use of modified/SR formulations
  • Establish goals at start of treatment
  • Frequent evaluation of ongoing requirements

Tolerance:

  • Does not occur with miosis, constipation and seizures
  • There is a moderate degree of tolerance to bradycardia

Precautions/contraindications of opioid analgesics
  • Use of pure agonists with weak partial agonists:
    • e.g. buprenorphine with morphine
    • Can reduce analgesia, and induce withdrawal
  • Head injury:
    • CO2 retention secondary to respiratory depression causes cerebral vasodilation
  • Pregnancy:
    • Chronic use may precipitate dependence in fetus
  • Impaired pulmonary function:
    • Risk of acute respiratory failure
  • Impaired hepatic or renal function
  • Endocrine disease:
    • Patients with Addison’s disease and hypothyroidism (myxedema) may have prolonged and exaggerated responses to opioids
  • Drug interactions:
    • Other sedative-hypnotics
    • Antipsychotic agents: increased sedation and accentuation of cardiovascular effects (antimuscarinic and alpha blocking actions)
    • MAOIs: high incidence of hyperpyrexic coma, hypertension

Further reading

References

Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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