Drug Interaction Report

GENERALLY AVOID: Coadministration with potent CYP450 3A4 inhibitors may increase the plasma concentrations and the risk of adverse effects of ribociclib, which is a substrate of the isoenzyme. In healthy subjects, administration of a single 400 mg dose of ribociclib with ritonavir (100 mg twice daily for 14 days), a potent CYP450 3A4 inhibitor, resulted in a 1.7-fold and 3.2-fold increase in ribociclib peak plasma concentration (Cmax) and systemic exposure (AUC), respectively, compared to ribociclib administered alone. In addition, administration of erythromycin, a moderate CYP450 3A4 inhibitor, is predicted to increase ribociclib Cmax and AUC by 1.3-fold and 1.9-fold, respectively. The risk of adverse effects such as infections, neutropenia, leucopenia, anemia, thrombocytopenia, nausea, vomiting, diarrhea, stomatitis, anorexia, alopecia, fatigue, headache, and abnormal liver function may be increased.

MANAGEMENT: Concomitant use of ribociclib with potent CYP450 3A4 inhibitors should generally be avoided. Alternative agents with no or minimal CYP450 3A4 inhibitory potential are recommended whenever possible. If no alternatives exist, the dose of ribociclib should be reduced to 400 mg once daily. Patients receiving concomitant treatment with a CYP450 3A4 inhibitor should be monitored for the development of ribociclib-related adverse effects. Following discontinuation of the potent CYP450 3A4 inhibitor, the ribociclib dosage should be returned (after at least 5 half-lives of the inhibitor) to that used prior to initiation of the inhibitor.

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: Administration with a high-fat meal may decrease the oral bioavailability of amprenavir. The mechanism is unknown. In healthy volunteers, consumption of a standardized high-fat meal decreased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of amprenavir (1200 mg single oral dose) by 36% and 21%, respectively, compared to administration in the fasted state. The time to reach Cmax (Tmax) was increased 44% following a high-fat meal.

Grapefruit juice does not appear to significantly affect the pharmacokinetics of amprenavir. In 12 healthy volunteers, administration with grapefruit juice (200 mL) decreased the mean peak plasma concentration (Cmax) of amprenavir (1200 mg single oral dose) by 22% compared to water. The median time to reach Cmax (Tmax) was prolonged from 0.75 to 1.13 hours. These pharmacokinetic changes are not thought to be clinically significant, since antiretroviral response is more closely associated with systemic exposure (AUC) and trough plasma concentration (Cmin), which were not affected in the study.

MANAGEMENT: Amprenavir may be taken with or without food, but should not be taken with a high-fat meal.

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.