Drug Interactions between afatinib and amoxicillin / clarithromycin / vonoprazan

ADJUST DOSE: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of afatinib, which is a substrate of the efflux transporter. In study subjects, oral administration of the P-gp inhibitor ritonavir (200 mg twice daily) one hour before afatinib dosing resulted in a 48% increase in afatinib systemic exposure. There was no change in afatinib exposure when ritonavir was administered simultaneously with, or 6 hours after, the afatinib dose.

MANAGEMENT: Caution is advised if afatinib is used in combination with P-gp inhibitors. Patients should be monitored for potentially increased adverse effects such as diarrhea, which may lead to dehydration with or without renal impairment; cutaneous reactions including rash, erythema, and bullous, blistering, or exfoliating lesions; interstitial lung disease such as lung infiltration, pneumonitis, acute respiratory distress syndrome, and allergic alveolitis; hepatotoxicity, which may be life-threatening or fatal; keratitis characterized by acute or worsening eye inflammation, lacrimation, light sensitivity, blurred vision, eye pain, red eye, and/or ulceration; and left ventricular dysfunction. The manufacturer recommends reducing the daily dose of afatinib by 10 mg if not tolerated. The previous dose may be resumed after discontinuation of the P-gp inhibitor as tolerated.

Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.