Clinical Pharmacology
Naloxone is a pure narcotic antagonist. It prevents or reverses the effects of opioids, including respiratory depression, sedation and hypotension. Naloxone does not possess agonist properties and therefore does not produce respiratory depression, psychotomimetic affects or pupillary constriction. In the absence of opioids it exhibits essentially no pharmacological activity. Naloxone antagonises the opioid effects by competitive inhibition at the opioid receptor sites.
Following parenteral administration naloxone is rapidly distributed in the body. It is metabolised in the liver, primarily by glucuronide conjugation and excreted in the urine. When administered intravenously its onset of action is rapid (within 2 minutes); the onset of action is only slightly less rapid when it is administered subcutaneously or intramuscularly. The duration of action is dependent upon the dose and route of administration. Intramuscular administration produces a more prolonged effect than intravenous administration.
Naloxone has not been shown to produce tolerance nor to cause physical or psychological dependence. No short-term toxicity has been observed but long-term safety has not been investigated. There is no clinical experience with naloxone overdosage in humans.
Possible Adverse Effects
- Abrupt reversal of narcotic depression may result in nausea, vomiting, sweating, tachycardia, increased blood pressure and tremulousness.
- Tachycardia, hypertension.
- Gastrointestinal disturbances (nausea, vomiting).
- Lethargy, tremors.
- Elevated PTT.
Special Precautions
- Infants receiving naloxone in the delivery room because of narcotic induced respiratory depression require observation afterwards. This observation need not necessarily be on the neonatal unit. See Naloxone guideline.
- The duration of naloxone antagonism may be less than the clearance of the opiate being antagonised. This should not be a problem with the intramuscular administration of naloxone. However, some babies may require a second dose of naloxone.
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