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The metabolism of Gefitinib is predominantly via CYP3A4. Co-administration with Rifampicin (a known potent CYP3A4 inducer) reduced mean Gefitinib AUC (see PRECAUTIONS).
Co-administration with Itraconazole (a CYP3A4 inhibitor) resulted in an increase in the mean AUC of Gefitinib. This increase may be clinically relevant since adverse experiences are related to dose and exposure.
Co-administration of Ranitidine at a dose that caused sustained elevations in gastric pH (≥ 5), resulted in a reduced mean Gefitinib AUC. As consequence, drug that cause significant sustained elevation in gastric pH may reduce plasma concentrations of GEFITERO and therefore may reduce plasma concentrations of GEFITERO and therefore may reduce efficacy (see PRECAUTIONS).
INR elevations and/or bleeding events have been reported in some patients taking Warfarin (see PRECAUTIONS).
