Drug Interaction Report

GENERALLY AVOID: Arsenic trioxide can cause QT interval prolongation and complete atrioventricular block. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. During clinical studies involving 40 patients receiving arsenic trioxide for acute promyelocytic leukemia, 16 of them (40%) had at least one ECG tracing with a QTc interval greater than 500 msec. Prolongation of QTc was observed between 1 and 5 weeks after arsenic trioxide infusion and returned towards baseline by the end of 8 weeks. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: If possible, medications that are known to prolong the QT interval should be discontinued prior to initiating therapy with arsenic trioxide and withheld for at least several weeks after completion of therapy. Caution is advised if concomitant use cannot be avoided. Patients should have frequent ECGs and be monitored for arrhythmias when QT interval is prolonged. An absolute QT interval exceeding 500 msec will require immediate action to correct concomitant risk factors, if any, as well as a thorough assessment of the need for continued therapy. Patients who develop syncope or arrhythmia should be hospitalized for clinical and laboratory monitoring. Arsenic trioxide should be temporarily discontinued until symptoms resolve, the QTc interval regresses to below 460 msec, and electrolyte abnormalities are corrected.

MONITOR: Coadministration with ribociclib may increase the plasma concentrations and pharmacologic effects of drugs that are substrates of CYP450 3A4. The proposed mechanism is decreased clearance due to ribociclib-mediated inhibition of CYP450 3A4 metabolism. In healthy study subjects, administration of midazolam, a sensitive CYP450 3A4 substrate, with multiple 400 mg daily doses of ribociclib increased the midazolam peak plasma concentration (Cmax) and systemic exposure (AUC) by 2.1-fold and 3.8-fold, respectively, compared to midazolam administered alone. When given at a clinically relevant dose of 600 mg daily, ribociclib is predicted to increase midazolam Cmax and AUC by 2.4-fold and 5.2-fold, respectively.

MANAGEMENT: Caution is advised when ribociclib is used concomitantly with drugs that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever ribociclib is added to or withdrawn from therapy.

GENERALLY AVOID: Pomegranates and grapefruit may increase the systemic exposure to ribociclib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in these fruits. Increased exposure to ribociclib may increase the risk of adverse effects such as infections, neutropenia, leukopenia, anemia, thrombocytopenia, anorexia, nausea, vomiting, diarrhea, stomatitis, alopecia, fatigue, headache, and abnormal liver function may be increased.

MANAGEMENT: Patients receiving ribociclib should avoid consumption of pomegranates or pomegranate juice and grapefruit or grapefruit juice during treatment.