Naloxone

 Common indications

• Treatment of opioid toxicity associated with respiratory and/or neurological depression.

 

Mechanisms of action

• Naloxone binds to opioid receptors (particularly the pharmacologically-important opioid µ-receptors), where it acts as a competitive antagonist. 
• It has little or no effect in the absence of an exogenous opioid (e.g. morphine). 
• However, if an opioid is present, naloxone displaces it from its receptors and, in so doing, it reverses its effects. 
• In opioid toxicity, this is used to restore an adequate level of consciousness and respiratory rate.

 

Important adverse effects

• Where naloxone is administered to reverse opioid toxicity in an opioid-dependent individual, an opioid withdrawal reaction may be precipitated. This presents with pain (if the opioid was being taken for its analgesic effect), restlessness, nausea and vomiting, dilated pupils, and cold, dry skin with piloerection (‘cold turkey’). 
• Naloxone has no other significant adverse effects.

 

Warnings

• There are no specific contraindications to the use of naloxone. 
• However, caution should be exercised in patients who may have developed opioid dependence (whether from therapeutic or recreational use) because of the risk of precipitating opioid withdrawal. 
• Lower doses should be used in the palliative care setting to reduce the risk of complete reversal of analgesia.

 

Important interactions

• Naloxone has no clinically important drug interactions other than its interaction with opioids, which is central to its pharmacological effect and practical use.