Drug Interactions between mitotane and repotrectinib

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations and adverse effects of repotrectinib. According to prescribing information, repotrectinib is primarily metabolized by CYP450 3A4, and is also a substrate of P-gp in vitro. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with repotrectinib and grapefruit juice but has been reported for other CYP450 3A4 inhibitors. Drug interaction studies have shown that the administration of repotrectinib with itraconazole, a potent CYP450 3A4 and P-gp inhibitor, increased the peak plasma concentration (Cmax) and systemic exposure (AUC) of repotrectinib by 1.7-fold and 5.9-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 repotrectinib may increase the risk of adverse reactions such as dizziness, fatigue, cognitive disorders, ataxia, dysgeusia, peripheral neuropathy, muscular weakness, and dyspnea as well as more serious adverse effects such as interstitial lung disease/pneumonitis, liver transaminase elevations, myalgia with creatinine phosphokinase (CPK) elevation, hyperuricemia, and skeletal fractures.

MANAGEMENT: The manufacturer advises that concomitant use of repotrectinib with grapefruit, grapefruit juice, or supplements that contain grapefruit should be avoided.

ADJUST DOSING INTERVAL: Fat-rich food enhances the absorption of mitotane. One study evaluated blood levels of mitotane (o,p'-DDD) after subjects ingested a single dose of 2 g administered using various delivery vehicles (e.g., tablets, granules, milk, chocolate or oil emulsion). Mitotane plasma levels were significantly higher for milk, chocolate, and oil emulsion when compared to those who received tablets or granules alone. In the same study, mitotane levels were evaluated in subjects following long-term treatment (total dose of 200 g over 30 to 60 days) in tablet, oil emulsion, or milk formulations. Significantly higher mean plasma levels were recorded in subjects who received mitotane as an oil emulsion or mixed in milk, when compared to tablets alone. Additionally, the recovery of o,p'-DDD from the feces was about 5 times higher in subjects who received tablets alone, suggesting absorption was reduced when compared to subjects who received mitotane mixed with a fat-rich vehicle (e.g., oil emulsion or milk).

GENERALLY AVOID: Concomitant use of mitotane with central nervous system (CNS) depressants, including alcohol, may potentiate adverse effects such as somnolence and sedation.

MANAGEMENT: According to product labeling, mitotane tablets should be taken during meals containing fat-rich food (e.g., milk, chocolate, or oil) and with a full glass of water. Patients should be advised to avoid or limit consumption of alcohol and to avoid activities requiring mental alertness such as driving or operating hazardous machinery until they know how the medication affects them.