Drug Interactions between fosamprenavir and idelalisib

MONITOR: Coadministration with inhibitors of CYP450 3A4 and/or P-glycoprotein (P-gp) may increase the plasma concentrations of idelalisib, which is a substrate of both the isoenzyme and efflux transporter. In healthy volunteers, administration of a single 400 mg dose of idelalisib with the potent CYP450 3A4 and P-gp inhibitor ketoconazole (400 mg daily for 4 days) resulted in a 1.8-fold increase in mean idelalisib systemic exposure (AUC). No change was observed in mean peak plasma concentration (Cmax).

MANAGEMENT: Caution is advised if idelalisib is prescribed in combination with CYP450 3A4 and/or P-gp inhibitors. Pharmacologic response to idelalisib should be monitored more closely whenever a CYP450 3A4/P-gp inhibitor is added to or withdrawn from therapy, and the idelalisib dosing adjusted or interrupted as necessary in accordance with the product labeling. Patients should be closely monitored for idelalisib toxicity such as hepatotoxicity, diarrhea, colitis, intestinal perforation, pneumonitis, neutropenia, and thrombocytopenia.