Morphine potential advantages

Although it is more toxic than morphine on a weight basis, methadone is more potent. On resolving the racemic compound, the (-) form was found to possess most of the opioid activities. The dextrorotatory isomer retains basically only the antitussive property (the commercial product is the racemic form). The potential advantages of methadone over morphine is its effectiveness via the oral route and considerably longer half-life (24-36 vs. 2- hours). This feature, particularly, has led to the drug s extensive use in the treatment of heroin addicts to suppress the latters abstinence syndrome by maintenance of patients with methadone only. 

Pethidine is widely used. There is little difference between the effects of equipotent doses of morphine and pethidine with regard to analgesia, respiratory depression, and nausea and vomiting (but it may delay labour less). AU opioids have the potential to cause respiratory depression of the newborn but this can be reversed with naloxone if necessary. The popular choice of pethidine for analgesia during labour in the UK is not because of any clear pharmacological advantage, but because it remains the only opioid licensed for use by midwives. 

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