Here we are however, thinking about a diagnostic test - will this challenge dose of opioid produce analgesia or won't it?
Naltrexone is an opioid antagonist that blocks the effect of opioids in the brain.
Drugs are used outside of their license e.g. aspirin for cardiovascular reasons or dihydrocodeine for opioid detoxification.
Pethidine has an atropine like effect that is said to counteract the opioid effect on smooth muscle but this has not been proven clinically.
Its insertion is stimulating but may be attenuated by using local anesthetic, a small bolus of propofol or a short acting opioid.