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Interacting Drugs

OBJECT DRUGS

Opioid Analgesics:

PRECIPITANT DRUGS

Enzyme Inducers:


Comment:

Enzyme inducers may increase the elimination of these opioids via CYP3A4 metabolism and other pathways. This may result in reduced analgesic effects and may cause withdrawal symptoms in patients maintained on methadone. For example, rifampin has been shown to markedly reduce oxycodone plasma concentrations. Potent enzyme inducers such as rifampin may have larger effects on these analgesics than other inducers. With codeine, rifampin reduced the conversion of codeine to morphine, but only in those with normal CYP2D6 activity (EMs). Rifampin did not interact with codeine in subjects with little CYP2D6 activity (PMs), but PMs are not likely to have adequate analgesic effects from codeine whether or not they are taking enzyme inducers such as rifampin. Ritonavir may have variable effects on these opioids, depending on the duration of ritonavir therapy and other factors. In one study, ritonavir increased fentanyl plasma concentrations.


Class 3: Assess Risk & Take Action if Necessary