ritlecitinib will improve the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Intently. Ritlecitinib inhibits CYP3A4 substrates; coadministration boosts AUC and peak plasma concentration sensitive substrates, which can enhance risk of adverse reactions.iloprost, fentanyl. Possibly increas