<p><strong>Anticoagulants</strong>: Interaction with coumarin-derived anticoagulants, including warfarin, leading to increased International Normalized Ratio (INR) and bleeding adverse reactions.<br />
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<strong>CYP3A4 inhibitors</strong>: Erlotinib is metabolized predominantly by CYP3A4. Co-treatment with the potent CYP3A4 inhibitor ketoconazole increased Erlotinib AUC by 67%. When Erlotinib was co-administered with Ciprofloxacin, an inhibitor of both CYP3A4 and CYP1A2, the Erlotinib exposure [AUC] and maximum concentration [Cmax] increased by 39% and 17%, respectively.<br />
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<strong>CYP3A4 inducers</strong>: Pre-treatment with the CYP3A4 inducer Rifampicin for 7-11 days prior to Erlotinib decreased Erlotinib AUC by 58% to 80%. Dose modifications are recommended.<br />
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<strong>Drugs affecting gastric pH</strong>: Co-administration of Erlotinib with omeprazole decreased Erlotinib AUC by 46% and co-administration of Erlotinib with Ranitidine 300 mg decreased Erlotinib AUC by 33%.</p>