Opioid antagonists and their therapeutic role in anaesthesia and chronic pain management

The use of opioids is often associated with less pain but more suffering in terms of unwanted side effects, some of which may lead to significant morbidity and even mortality. In an attempt to address this problem, numerous alterations were made to the original molecules found in the opium plant. Among others, heroin, methadone and the phenylpiperidine derivatives (fentanyl, pethidine, etc.) were synthesised and all claimed advantages over morphine, although they had the same degree of side effects as the original drug. A notable example is pethidine, which was synthesised in the 1930s and claimed less respiratory depression than morphine (an opinion that is still held by some of our colleagues).1