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Naloxone. By A. Spicer

Mode of operation

Naloxone blocks three (delta, kappa and mu although some sources also include sigma receptor) opioid receptor subtypes via direct competition thus making it an opioid antagonist. It therefore blocks the usual effects of opioids which are varying degrees of coma, respiratory depression and pinpoint pupils.

Naloxone reverses both exogenous and endogenous opioids (endorphins, enkephalins, and dynorphins). It has no agonist properties; and, in the absence of opioids, naloxone exhibits little significant pharmacologic activity.

Naloxone is metabolised in the liver, has a half life of 1/2 hour to 1 1/2 hours and is excreted in urine and bile.

Side effects

Nausea & vomiting

Contraindications

None listed

Cautions

Physical dependence on opioids

Cardiac irritability, cardiac disease or those receiving cardiotoxic drugs

Pain

Interactions

None listed

Monitoring

Naloxone will immediately reverse opioid-induced respiratory depression but the dose may have to be repeated because of the short duration of action of naloxone.

No specific monitoring listed.

Dose

Doses used in acute opioid overdose.

By intravenous injection, 0.4-2 mg repeated at intervals of 2-3 minutes to a max. of 10 mg if respiratory function does not improve (then question diagnosis); CHILD 10 micrograms/kg; subsequent dose of 100 micrograms/kg if no response.

By subcutaneous or intramuscular injection, ADULT and CHILD as intravenous injection but only if intravenous route not feasible (onset of action slower).

By continuous intravenous infusion using an infusion pump, 10 mg diluted in 50 mL intravenous infusion solution at a rate adjusted according to the response (initial rate may be set at 60% of the initial intravenous injection dose and infused over 1 hour).

Doses used for the reversal of postoperative opioid-induced respiratory depression.

By intravenous injection, 100-200 micrograms (1.5-3 micrograms/kg); if response inadequate, increments of 100 micrograms every 2 minutes; further doses by intramuscular injection after 1-2 hours if required.

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