Drug Interaction Report

MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of pralsetinib, which is primarily metabolized by the isoenzyme. A physiologically based pharmacokinetic (PBPK) model predicted pralsetinib's peak plasma concentration (Cmax) and systemic exposure (AUC) would increase by 1.2- and 2.2-fold, respectively, when coadministered with the potent CYP450 3A4 inhibitor voriconazole (400 mg twice daily on Day 1, followed by 200 mg twice daily). Similarly, another PBPK model predicted that concomitant use of the moderate CYP450 3A4 inhibitor fluconazole (400 mg daily) would increase the Cmax and AUC of pralsetinib by 1.2- and 1.7-fold, respectively. The extent to which other, less potent CYP450 3A4 inhibitors may interact with pralsetinib is unknown. Increased exposure to pralsetinib may increase the risk and/or frequency of adverse effects such as interstitial lung disease/pneumonitis, liver transaminase elevations, hypertension, and hemorrhage. Some clinical trials have also observed prolongation of the QT interval in patients on pralsetinib, though this was not observed in a study of 34 patients with rearranged during transfection (RET)-altered solid tumors on pralsetinib at the recommended dosage.

MANAGEMENT: Caution is advised when pralsetinib is used with CYP450 3A4 inhibitors. Monitor closely for adverse effects whenever a CYP450 3A4 inhibitor is added to therapy. Alternative treatments may be required if an interaction is suspected.

ADJUST DOSING INTERVAL: Food significantly increases the oral bioavailability of pralsetinib. According to the product labeling, administration of pralsetinib (200 mg) with a high-fat meal (approximately 800 to 1000 calories; 50% to 60% from fat) increased mean pralsetinib peak plasma concentration (Cmax) and systemic exposure (AUC) by 104% and 122%, respectively. The median time to maximum concentration (Tmax) was delayed from 4 hours to 8.5 hours, when compared to the fasted state.

GENERALLY AVOID: The juice of grapefruit and/or Seville oranges may increase the plasma concentrations of pralsetinib. 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. 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 pralsetinib may increase the risk of adverse effects such as interstitial lung disease/pneumonitis, liver transaminase elevations, hypertension, and hemorrhage. Some clinical trials have also observed prolongation of the QT interval in patients on pralsetinib, though this was not observed in a study of 34 patients with rearranged during transfection (RET)-altered solid tumors on pralsetinib at the recommended dosage.

MANAGEMENT: Pralsetinib should be administered on an empty stomach, with no food intake recommended for at least 2 hours before and at least 1 hour after taking the medication. Patients should avoid consumption of grapefruit, grapefruit juice, Seville oranges, or Seville orange juice during treatment with pralsetinib.