Drug Interactions between ivacaftor / lumacaftor and trabectedin

GENERALLY AVOID: Coadministration with potent inducers of CYP450 3A4 may decrease the plasma concentrations of trabectedin, which is primarily metabolized by the isoenzyme. In 9 study patients with advanced malignancies, administration of a single 1.3 mg/m2 infusion of trabectedin on day 6 of treatment with rifampin (600 mg daily for 6 days), a potent CYP450 3A4 inducer, resulted in a 22% decrease in mean trabectedin peak plasma concentration (Cmax) and 31% decrease in mean systemic exposure (AUC) compared to infusion of trabectedin alone. Most trabectedin-related toxicities including nausea, thrombocytopenia, neutropenia, leukopenia, and liver function abnormalities occurred at a higher frequency with trabectedin alone compared to trabectedin coadministered with rifampin. Grade 3 and 4 adverse events were also observed more often with trabectedin alone. Only vomiting and fatigue were reported more often during coadministration of trabectedin with rifampin.

MANAGEMENT: Given the potential for diminished pharmacologic effects of trabectedin in the presence of potent CYP450 3A4 inducers, concomitant use should generally be avoided.

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MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of trabectedin, which is primarily metabolized by the isoenzyme. In eight study patients with advanced malignancies, administration of a single 0.58 mg/m2 infusion of trabectedin following the second dose of ketoconazole (200 mg twice daily for 15 doses), a potent CYP450 3A4 inhibitor, increased the dose-normalized mean trabectedin peak plasma concentration (Cmax) and systemic exposure (AUC) by 22% and 66%, respectively, compared to infusion of a single 1.3 mg/m2 dose of trabectedin alone.

MONITOR: Coadministration of trabectedin with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Reversible, acute increases in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) have occurred frequently in patients treated with trabectedin alone or with pegylated liposomal doxorubicin in clinical trials. In one U.S. trial with 378 patients, grade 3 or 4 elevated liver function tests (defined as elevations in ALT, AST, total bilirubin, or alkaline phosphatase) were reported in 35% of patients receiving trabectedin. ALT or AST elevations greater than eight times the upper limit of normal (ULN) occurred in 18% of patients, and drug-induced liver injury (defined as concurrent elevations in ALT or AST more than three times ULN, alkaline phosphatase less than two times ULN, and total bilirubin at least two times ULN) occurred in 1.3% of patients.

MANAGEMENT: Caution is advised when trabectedin is prescribed with CYP450 3A4 inhibitors that are also potentially hepatotoxic (e.g., azole antifungal agents; bicalutamide; cyclosporine (high dosages); dronedarone; macrolide antibiotics; protein kinase inhibitors; zafirlukast). Patients should be monitored for toxicities such as myelosuppression, rhabdomyolysis, hepatotoxicity, and cardiomyopathy, and the trabectedin dosage adjusted accordingly or treatment discontinued as necessary. Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice. Monitoring of alkaline phosphatase, bilirubin, AST, and ALT should occur regularly during trabectedin treatment in accordance with the product labeling, or as often as necessary when clinical symptoms develop. Trabectedin must not be used in patients with elevated bilirubin at the time of initiation of cycle. Elevated liver function tests should be managed with treatment interruption, dosage reduction, or permanent discontinuation depending on the severity and duration of abnormality.

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