It has been suggested that
opioids decrease oral ciprofloxacin levels, but good evidence for this appears to be lacking.
The manufacturers of ciprofloxacin state that the use of ciprofloxacin tablets is not recommended with opiate premedicants due to the risks of inadequate ciprofloxacin levels. Note that both high-dose methadone and some
quinolones (gatifloxacin,
levofloxacin, moxifloxacin and in particular sparfloxacin) may prolong the QT interval, see drugs that prolong the QT interval.