Drug Interaction Report

MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of gefitinib, which is primarily metabolized by the isoenzyme. According to the product labeling, administration of gefitinib (250 mg single dose) with the potent inhibitor itraconazole (200 mg once a day for 12 days) increased the mean gefitinib systemic exposure (AUC) by 88% in healthy male volunteers. This increase may be clinically significant, as adverse events of gefitinib are related to dose and exposure.

MANAGEMENT: Caution is advised if gefitinib is administered with CYP450 3A4 inhibitors, particularly potent ones like itraconazole, ketoconazole, posaconazole, voriconazole, clarithromycin, telithromycin, conivaptan, idelalisib, nefazodone, cobicistat, delavirdine, and most protease inhibitors. Pharmacologic response to gefitinib should be monitored more closely whenever a CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the dosage adjusted as necessary. Patients should be advised to contact their physician if they experience possible symptoms of gefitinib toxicity such as severe diarrhea, nausea, dyspnea, cough, and fever.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.