Pethidine (meperidine) and chlorpromazine
can be used together to enhance analgesia and for premedication before anaesthesia, but increased respiratory depression
, sedation, CNS toxicity
and hypotension can also occur. Similar effects would be expected with other phenothiazines and opioids
The combination need not be avoided, but care obviously needs to be taken. The US manufacturer suggests that the dose of pethidine (meperidine) should be proportionally reduced (usually by 25 to 50%) when it is given with phenothia- zines. Note that additive QT-prolonging effects are possible with methadone, see drugs that prolong the QT interval.