Ritonavir decreased
pethidine levels but increased norpethidine levels, which may possibly increase
toxicity on long-term use.
The manufacturers of
pethidine oral preparations and injection contraindicate or advise against its use with
ritonavir because of the risk of norpethidine
toxicity. Long-term use of
pethidine with other
protease inhibitors that are given with low- dose
ritonavir is also not recommended.