Drug Interaction Report

Coadministration with inhibitors of CYP450 3A4 may modestly increase the plasma concentrations of ropivacaine. Although ropivacaine is primarily metabolized by CYP450 1A2, it has been shown to undergo some metabolism via CYP450 3A4. In eight healthy volunteers, pretreatment with the 3A4 inhibitor erythromycin (500 mg three times a day for 6 days) was found to have only minor effects on the pharmacokinetics of a single dose of ropivacaine (0.6 mg/kg IV over 30 minutes) compared to placebo. However, in combination with the potent 1A2 inhibitor fluvoxamine (100 mg daily), erythromycin further increased the area under the plasma concentration-time curve (AUC) of ropivacaine by 50% compared to fluvoxamine alone, which increased the ropivacaine AUC by 3.7-fold. Fluvoxamine alone prolonged the elimination half-life of ropivacaine from 2.3 to 7.4 hours, while the addition of erythromycin further increased the half-life to 11.9 hours. In another study, pretreatment with the potent 3A4 inhibitor ketoconazole (100 mg twice daily for 2 days) decreased the mean total plasma clearance of ropivacaine (40 mg IV over 20 minutes) by just 15% in 12 healthy volunteers. Thus, it appears that CYP450 3A4 inhibitors may only have a significant effect on the pharmacokinetics of ropivacaine in the presence of a CYP450 1A2 inhibitor such as fluvoxamine, ciprofloxacin, or mexiletine.

GENERALLY AVOID: Grapefruit juice and Seville oranges may increase the plasma concentrations of entrectinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit and Seville oranges Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice, but pharmacokinetic data are available for the potent CYP450 3A4 inhibitor, itraconazole. When a single 100 mg dose of entrectinib was administered with itraconazole, entrectinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 1.7- and 6-fold, respectively. Coadministration of entrectinib with a moderate CYP450 3A4 inhibitor is predicted to increase entrectinib Cmax and AUC by 2.9- and 3-fold, respectively. 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. Increased exposure to entrectinib may increase the risk and/or severity of adverse effects such as cognitive impairment, mood disorders, dizziness, sleep disturbances, liver enzyme elevations, hyperuricemia, congestive heart failure, edema, myocarditis, QT prolongation, vision problems, anemia, and neutropenia.

MANAGEMENT: Patients should avoid consumption of grapefruit, grapefruit juice, and Seville oranges during treatment with entrectinib.