Drug Interaction Report

MONITOR: The concomitant use of myelosuppressive, immunosuppressive, or cytotoxic agents may potentiate and/or prolong the bone marrow toxicity associated with niraparib. Thrombocytopenia, anemia, neutropenia, and/or pancytopenia have all been observed with niraparib during clinical trials, especially during the initial phase of treatment. Additionally, myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) have been reported in patients treated with niraparib. Some cases were fatal, and the duration of therapy with niraparib in patients who developed MDS/AML varied from less than 1 month to approximately 6 years. All patients had previous chemotherapy with platinum agents and/or other DNA-damaging agents, including radiotherapy.

MANAGEMENT: Caution is advised if niraparib is prescribed with other myelosuppressive, immunosuppressive, or cytotoxic agents. Do not start niraparib until patients have recovered from hematological toxicity caused by previous chemotherapy (Grade 1 or less). Complete blood counts should be monitored as recommended in the product labeling and any relevant institutional protocols. Recommendations for dose adjustments as well as treatment interruption and discontinuation can also be found in the product labeling for serious hematologic adverse reactions. If hematological toxicities have not resolved within 4 weeks after interruption, discontinue niraparib and refer the patient to a hematologist for further investigations, including bone marrow analysis and blood sample for cytogenetics. If MDS/AML is confirmed, discontinue niraparib. Patients should be advised to contact their physician if they experience pale skin, weakness, fatigue, fever, weight loss, infections, shortness of breath, unusual bleeding or bruising, or blood in urine or stool.

GENERALLY AVOID: Grapefruit and/or grapefruit juice may increase the plasma concentrations of zanubrutinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice, but has been reported for other CYP450 3A4 inhibitors. When zanubrutinib was coadministered with the potent CYP450 3A4 inhibitor itraconazole (200 mg once daily), zanubrutinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased 157% and 278%, respectively, in healthy volunteers. Data evaluating coadministration of zanubrutinib, in patients with B-cell lymphoma, and several other known CYP450 3A4 inhibitors have been reported. When zanubrutinib was coadministered with another CYP450 3A4 inhibitor, clarithromycin (250 mg twice daily), zanubrutinib Cmax and AUC increased 101% and 92%, respectively. The moderate CYP450 3A4 inhibitor diltiazem (180 mg once daily) increased both zanubrutinib Cmax and AUC increased by 62%. Another moderate CYP450 3A4 inhibitor, fluconazole (400 mg once daily), increased zanubrutinib Cmax and AUC 81% and 88%, respectively. Clinical data for less potent inhibitors are not available. In general, the effects of grapefruit products are concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Increased zanubrutinib exposure may potentiate the risk of toxicities such as hemorrhage, infection, cytopenias, malignancies, and serious cardiac arrhythmias, primarily atrial fibrillation and atrial flutter.

Food does not affect the oral bioavailability of zanubrutinib. No clinically significant differences in zanubrutinib Cmax or AUC were observed following administration of a high-fat meal (approximately 1000 calories; 50% from fat) in healthy subjects.

MANAGEMENT: Zanubrutinib may be administered with or without food. Patients should avoid consumption of grapefruit, grapefruit juice, Seville oranges (a citrus relative of the grapefruit), and Seville orange juice during treatment with zanubrutinib. Close clinical monitoring for development of zanubrutinib-related toxicities, dosage adjustments, and/or withholding treatment in accordance with product labeling is advised. Additional consultation with individual package labeling, as well as relevant institutional protocols, may be advisable for further guidance.