UNCONTROLLED WHEN PRINTED

Introduction

  • Naloxone is a clear colourless solution that is a pure narcotic antagonist that exerts its effect by competitive inhibition at the opioid receptor sites. It prevents or reverses the effects of opioids, including respiratory depression, sedation and hypotension. In the absence of opioids it exhibits essentially no pharmacological activity.

Uses within SJA

  • Reverse of respiratory depression in a suspected narcotic overdose.
  • Naloxone is no longer used in cardiac arrest, as the cause of the arrest is from hypoxia and the administration of naloxone will have no direct effect on the reversal of this during cardiac arrest.

Pharmacokinetics

Onset

  • When naloxone hydrochloride is administered intravenously the onset of action is observed within two minutes. The onset of action is only slightly less rapid when it is administered subcutaneously or intramuscularly (IM).
  • The duration of action is dependent upon the dose and route of administration of naloxone. IM administration produces a more prolonged effect than intravenous administration.

Distribution

  • Following administration, naloxone is rapidly distributed in the body.

Metabolism

  • Naloxone is metabolised in the liver, primarily by glucuronide conjugation.

Excretion

  • Excreted in the urine.

Pharmacodynamics

Desired Effects

  • Used for the complete or partial reversal of narcotic depression, including respiratory depression, induced by opioids including natural and synthetic narcotics, methadone and the narcotic antagonist analgesics.
  • Also used (in prehospital environment) for suspected acute opioid overdose to restore active respiratory function.

Side Effects

  • Abrupt reversal of narcotic depression may result in:
    • Nausea
    • Vomiting
    • Sweating
    • Headache
    • Nervousness
    • Tachycardia
    • Increased blood pressure
  • Rarely, when large doses of naloxone are administered, a significant reversal of analgesia can be observed.

Duration of Action

  • The onset of action is apparent within a few minutes but duration of action can range from 30 minutes to one and a half hours. It is important to remember that the half life of morphine (and most of its derivatives) is significantly longer than naloxone, therefore patients often require multiple administrations of naloxone.

Other Drug Interactions

  • Because naloxone reverses the analgesic and other effects of opioid agonist/antagonists, it may cause withdrawal symptoms if used concurrently with these drugs in physically dependent patients (eg. Patients receiving methadone to treat opioid dependence).
  • When naloxone is used post-operatively to reverse the central depressive effects of opioid agonists used as anaesthesia adjuncts, the dose of naloxone must be carefully titrated to achieve the desired effect without interfering with control of post-operative pain, or causing other adverse effects.

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