Drug Interactions between Abraxane and regorafenib

MONITOR: Coadministration with inhibitors of CYP450 3A4, such as grapefruit juice, may increase the plasma concentrations of paclitaxel, which is a substrate of the isoenzyme. Current data suggest that consumption of large quantities of grapefruit juice inhibit both intestinal and hepatic CYP450 3A4 due to certain compounds present in grapefruit. Specific data for paclitaxel are lacking; however, in a case report of a 52-year-old woman with esophageal squamous cell carcinoma receiving a twice weekly chemotherapy regimen including intravenous docetaxel (40 mg/m2) reported that docetaxel systemic exposure (AUC) increased by 65% compared with the AUC target of 1.96 mg*h/L and clearance decreased by 63%, with a 71% reduction in the patient's neutrophil count. In the absence of other CYP450 3A4 inhibitors, these effects were attributed to daily consumption of 250 mL of grapefruit juice, which the patient had been consuming for at least 3 months. Two weeks after the patient ceased the grapefruit juice, the docetaxel AUC was closer to the target value and the neutrophil count reduction was less than 35%. In addition, in a pharmacokinetic study consisting of 7 cancer patients, mean dose-normalized docetaxel AUC increased by 2.2-fold and clearance decreased by 49% when intravenous docetaxel was given at a reduced dosage of 10 mg/m2 in combination with the potent CYP450 3A4 inhibitor ketoconazole (200 mg orally once daily for 3 days) compared to docetaxel administered alone at 100 mg/m2.

MANAGEMENT: Caution is recommended if paclitaxel is to be used in combination with grapefruit and grapefruit juice. Patients should be closely monitored for the development of paclitaxel toxicity, including diarrhea, mucositis, myelosuppression, and peripheral neuropathy and dose adjustment considered per local treatment protocols.

ADJUST DOSING INTERVAL: Depending on the amount of fat, food may enhance the oral bioavailability of both regorafenib and its active metabolites, M-2 and M-5. In 24 healthy male subjects, administration of regorafenib with a high-fat meal (945 calories; 54.6 g fat) increased the mean systemic exposure (AUC) of regorafenib by 48% but decreased the mean AUC of M-2 and M-5 by 20% and 51%, respectively, compared to administration under the fasted state. In contrast, administration with a low-fat meal (319 calories; 8.2 g fat) increased the mean AUC of regorafenib, M-2 and M-5 by 36%, 40% and 23%, respectively, compared to administration during fasting.

GENERALLY AVOID: Coadministration with grapefruit juice may alter the pharmacokinetics of regorafenib and its active metabolites. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. The interaction has not been studied specifically with grapefruit juice, but has been reported with the potent CYP450 3A4 inhibitor, ketoconazole. In 18 healthy male study subjects, administration of a single 160 mg dose of regorafenib on day 5 of treatment with ketoconazole (400 mg daily for 18 days) resulted in a 33% increase in mean regorafenib systemic exposure (AUC) compared to administration of regorafenib alone. Additionally, there was a 93% decrease each in the mean AUC of the M-2 and M-5 metabolites. Both have been shown to have similar in vitro pharmacological activity and steady-state concentrations as regorafenib, thus the net clinical effect of these pharmacokinetic changes is unknown.

MANAGEMENT: To ensure optimal oral absorption, regorafenib should be administered with a low-fat breakfast that contains less than 30% fat. Examples of a low-fat breakfast include: 2 slices of white toast with 1 tablespoon of low-fat margarine and 1 tablespoon of jelly, plus 8 ounces of skim milk (319 calories; 8.2 g fat); or 1 cup of cereal, 8 ounces of skim milk, 1 slice of toast with jam, apple juice, and 1 cup of coffee or tea (520 calories; 2 g fat). Patients should be advised to avoid consuming grapefruit or grapefruit juice during treatment with regorafenib.