Cimetidine increases the
plasma levels of alfentanil, and some preliminary observa- tions suggest that
cimetidine may increase the effects of fentanyl. Isolated reports describe adverse reactions in patients taking methadone, morphine, or mixed opium alkaloids when
cimetidine was also given, or morphine when ranitidine was also given.
The
clinical relevance of these effects on alfentanil and fentanyl are unknown. The case reports are not expected to be of general significance.