<unk>  is metabolized by the enzymes CYP3A4 and CYP2D6. Therefore, its clearance can be altered by inhibitors and inducers of these enzymes, increasing and decreasing half-life, respectively. (For lists of CYP3A4 and CYP2D6 inhibitors and inducers, see here and here, respectively.) Natural genetic variation in these enzymes can also influence the clearance of<unk> , which may be related to the wide inter-individual variability in its half-life and potency. Ritonavir or lopinavir/ritonavir greatly increase plasma concentrations of<unk>  in healthy human volunteers due to inhibition of CYP3A4 and CYP2D6. Rifampicin greatly reduces plasma concentrations of<unk>  due to strong induction of CYP3A4. There is also a case report of fosphenytoin, a CYP3A4 inducer, dramatically reducing the analgesic effects of<unk>  in a chronic pain patient. Dosage or medication adjustments may be necessary in each case.
Oxycodone
Hydrocodone
Codeine
Morphine
Noroxycodone
Norhydrocodone
Tramadol
Piperoxan