Ritonavir is predicted to increase the effects of
dextropropoxyphene. Other
protease inhibitors may also be expected to interact similarly but there seems little documented about these effects in practice.
The UK manufacturer of
ritonavir contraindicates its use with dextropropoxy- phene as extremely raised
dextropropoxyphene levels may occur, which would increase the risk of serious adverse events (e.g. respiratory depression). However, the US manufacturer only suggests that a dose decrease may be needed.