Naloxone acts as a pure antagonist at opioid receptors. It is rapidly metabolised by the liver and has a half-life of approximately 1 hour. It is used to reverse sedation and respiratory depression after opioid overdose and intoxication.

Patients should be monitored frequently and repeat doses may need to be given at a later time because naloxone has a shorter half-life than most of the commonly used opioids. Too rapid reversal can precipitate acute withdrawal, hypotension, acute pulmonary oedema and/or a recurrence of pain. Dose requirements are extremely variable, depending on the dose of opioid to be antagonised.

To avoid re-emergence of opioid adverse effects, ensure that patches are removed before reversal, and determine what long-acting formulations have been administered, so that treatment with naloxone can be adjusted accordingly.

It may be possible to avoid a patient relapsing into narcosis after overdose by the use of an infusion of naloxone; this is particularly useful when long-acting drugs or formulations have been taken.

Naloxone should not be used routinely in undifferentiated coma. It should only be used if opioid intoxication is suspected based on the clinical history and examination. Naloxone may result in severe withdrawal and aggression in chronic narcotic abusers. Uncooperative patients may not be willing to undergo further observation upon waking. The aim should be to avoid dangerously depressed levels of consciousness or respiration that may require intubation, rather than achieving full alertness. In the hospital setting where there are staff with advanced airway skills, careful observation may be the best management. Where these skills do not exist, full reversal is preferred. In all cases, initial basic life support measures, must still take priority over naloxone administration.

For reversal of opioid sedation and respiratory depression in adults in the postoperative setting, naloxone can be given in 100 microgram increments intravenously, every 2 minutes until the desired effect is obtained (more frequent injection may be required if the patient is apnoeic) or, by diluting 1 ampoule (400 micrograms/mL) to 10 mL with sterile normal saline, it can be given in 1 mL (ie 40 micrograms) increments and titrated against response. This may avoid the severe pain occurring when the analgesic effect of the opioid is suddenly reversed.

Naloxone appears to be the most reliable and cost-effective form of treatment for opioid-induced pruritus. A dose of 120 micrograms subcutaneously is used.