Drug Interactions between ivacaftor / lumacaftor and sirolimus protein-bound

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.

GENERALLY AVOID: Coadministration of protein-bound sirolimus intravenous suspension with potent inducers of CYP450 3A4 and/or P-glycoprotein (P-gp) may significantly decrease the systemic exposure to sirolimus, which is a known substrate for both the isoenzyme and efflux transporter. No formal studies evaluating the drug interaction potential of protein-bound sirolimus have been conducted. However, significant decreases in systemic exposure have been reported for oral sirolimus coadministered with potent inducers of CYP450 3A4 and/or P-gp such as rifampin. When a single 20 mg dose of sirolimus oral solution was administered to 14 healthy volunteers following pretreatment with rifampin 600 mg daily for 14 days, mean sirolimus peak blood concentration (Cmax) and systemic exposure (AUC) decreased by 71% and 82%, respectively. Reduced efficacy of protein-bound sirolimus may occur.

MANAGEMENT: Concomitant use of protein-bound sirolimus with potent CYP450 3A4 and/or P-gp inducers should generally be avoided.