Be advised if patient is taking other drugs, including non-prescription and natural health products, because they may speed up or slow down the breakdown of APO-ERLOTINIB. For example: Antifungals (such as ketoconazole, fluconazole); Calcium channel blockers (such as diltiazem, verapamil); Macrolide antibiotics (such as erythromycin, clarithromycin); Fluoroquinolone antibiotics (such as ciprofloxacin, norfloxacin); Other antibiotics (such as rifampin); Some antivirals (such as ritonavir, indinavir); Grapefruit juice; St. John's Wort; Anticonvulsants such as carbamazepine and phenytoin; Blood thinners such as warfarin; Medications which reduce acid in the stomach (such as omeprazole, ranitidine); Statin drugs to treat high cholesterol.