The concurrent use of pethidine (meperidine) and an MAOI has resulted in a serious and potentially life-threatening reaction in several patients. Excitement, muscle rigidity, hyperpyrexia, flushing, sweating and unconsciousness can occur very rapidly. Respiratory depression and hypertension or hypotension have also been seen. Similar interactions have been seen if tramadol is taken with
MAOIs. Isolated cases of adverse reactions (e.g. hypertension, hypotension, hyperthermia and tachycardia) have been reported after fentanyl or morphine were given to patients taking
MAOIs.
The interaction with pethidine is serious and potentially fatal, but the
incidence is probably quite low. It may therefore be an idiosyncratic reaction. Nevertheless, it would be imprudent to give pethidine (meperidine) to any patient taking an MAOI. Bear in mind that the non-selective
MAOIs are all essentially irreversible so that an interaction is possible for many days after their withdrawal (at least 2 weeks is the official advice). The manufacturers of tramadol contraindicate its use with
MAOIs because of the risks of this reaction. Evidence for an interaction between other
opioids and
MAOIs is limited, and some of the cases appear to represent a different type of reaction to that seen with pethidine. Indeed, with some
opioids there is evidence of safe concurrent use. Nevertheless, the manu- facturers of many
opioids contraindicate the use of
MAOIs. These include alfentanil,
codeine, diamorphine, fentanyl, hydromorphone, methadone, and oxycodone.