Drug Interaction Report

ADJUST DOSE: Coadministration of protein-bound sirolimus intravenous suspension with moderate or weak inhibitors of CYP450 3A4 may increase the systemic exposure to sirolimus, which is primarily metabolized by the isoenzyme and also a substrate of the P-glycoprotein (P-gp) efflux transporter. No formal studies evaluating the drug interaction potential of protein-bound sirolimus have been conducted. However, significant increases in systemic exposure have been reported for oral sirolimus coadministered with moderate dual inhibitors of CYP450 3A4 and P-gp such as diltiazem, erythromycin and verapamil, all of which are also substrates of CYP450 3A4 and P-gp. When 10 mg of sirolimus oral solution was administered with 120 mg of diltiazem in 18 healthy volunteers, sirolimus peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 1.4- and 1.6-fold, respectively. Sirolimus did not affect the pharmacokinetics of either diltiazem or its metabolites, desacetyldiltiazem and desmethyldiltiazem. When sirolimus oral solution 2 mg once a day was coadministered with erythromycin ethylsuccinate 800 mg every 8 hours to steady state in 24 healthy volunteers, sirolimus Cmax and AUC increased by 4.4- and 4.2-fold, respectively, while erythromycin Cmax and AUC increased by 1.6- and 1.7-fold, respectively. Likewise, when sirolimus oral solution 2 mg once a day was coadministered with verapamil 180 mg every 12 hours to steady state in 25 healthy volunteers, sirolimus Cmax and AUC increased by 2.3- and 2.2-fold, respectively, while Cmax and AUC of the pharmacologically active S(-) enantiomer of verapamil both increased by 1.5-fold. Increased exposures to sirolimus may increase the risk of adverse effects such stomatitis, nausea, diarrhea, vomiting, myelosuppression, infections, hypokalemia, hyperglycemia, interstitial lung disease, edema, rash, alopecia, and hemorrhage.

MANAGEMENT: When administered concomitantly with moderate or weak CYP450 3A4 inhibitors, the manufacturer recommends reducing the dosage of protein-bound sirolimus intravenous suspension to 56 mg/m2. Clinical response and toxicities should be closely monitored, and the dosage of protein-bound sirolimus further adjusted as necessary. In addition, patients may also require monitoring for potentially increased effects of concomitant CYP450 3A4 inhibitors, as many are also substrates of CYP450 3A4 and/or P-gp and may be impacted by sirolimus. The prescribing information for concomitant medications should be consulted.

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.

GENERALLY AVOID: Coadministration of protein-bound sirolimus intravenous suspension with grapefruit juice may increase the systemic exposure to sirolimus. The proposed mechanism is inhibition of CYP450 3A4-mediated metabolism of sirolimus by certain compounds present in grapefruit. However, grapefruit juice primarily inhibits CYP450 3A4-mediated first-pass metabolism in the gut wall and may have limited effects on medications that are not administered orally. No formal studies evaluating the drug interaction potential of protein-bound sirolimus have been conducted. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (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.

MANAGEMENT: The manufacturer recommends avoiding grapefruit and grapefruit juice during treatment with protein-bound sirolimus.