7.1Effect of Fosaprepitant/Aprepitant on the Pharmacokinetics of Other Drugs
When administered intravenously, fosaprepitant, a prodrug of aprepitant, is converted to aprepitant within 30 minutes. Therefore, drug interactions following administration of Fosaprepitant for Injection are likely to occur with drugs that interact with oral aprepitant. Fosaprepitant, given as a single 150-mg dose, is a weak inhibitor of CYP3A4, and the weak inhibition of CYP3A4 continues for 2 days after single dose administration.
Single dose fosaprepitant does not induce CYP3A4. Aprepitant is a substrate, an inhibitor, and an inducer of CYP3A4. Aprepitant is also an inducer of CYP2C9 [see Clinical Pharmacology ( 12.3 )] . Some substrates of CYP3A4 are contraindicated with Fosaprepitant for Injection [see Contraindications ( 4 )] . Dosage adjustment of some CYP3A4 and CYP2C9 substrates may be warranted, as shown in Table 7. Table 7 Effects of Fosaprepitant/Aprepitant on the Pharmacokinetics of Other Drugs CYP3A4 Substrates Pimozide Clinical Impact Increased pimozide exposure Intervention Fosaprepitant for Injection is contraindicated [see Contraindications ( 4 )] .
Benzodiazepines Clinical Impact Increased exposure to midazolam or other benzodiazepines metabolized via CYP3A4 (alprazolam, triazolam) may increase the risk of adverse reactions [see Clinical Pharmacology ( 12.3 )] . Intervention Monitor for benzodiazepine-related adverse reactions. Dexamethasone Clinical Impact Increased dexamethasone exposure [see Clinical Pharmacology ( 12.3 )] . Intervention Reduce the dose of oral dexamethasone by approximately 50% [see Dosage and Administration (2.1)] .
Methylprednisolone Clinical Impact Increased methylprednisolone exposure [see Clinical Pharmacology ( 12.3 )] . Intervention Reduce the dose of oral methylprednisolone by approximately 50% on Days 1 and 2 for patients receiving HEC and on Day 1 for patients receiving MEC. Reduce the dose of intravenous methylprednisolone by 25% on Days 1 and 2 for patients receiving HEC and on Day 1 for patients receiving MEC. Chemotherapeutic agents that are metabolized by CYP3A4 Clinical Impact Increased exposure of the chemotherapeutic agent may increase the risk of adverse reactions [see Clinical Pharmacology (12.3)] .
Intervention Vinblastine, vincristine, or ifosfamide or other chemotherapeutic agents Monitor for chemotherapeutic-related adverse reactions. Etoposide, vinorelbine, paclitaxel, and docetaxel No dosage adjustment needed. Hormonal Contraceptives Clinical Impact Decreased hormonal exposure during administration of and for 28 days after administration of the last dose of Fosaprepitant for Injection [see Warnings and Precautions ( 5.5 ), Use in Specific Populations ( 8.3 ), Clinical Pharmacology ( 12.3 )] .
Intervention Effective alternative or back-up methods of contraception (such as condoms or spermicides) should be used during treatment with Fosaprepitant for Injection and for 1 month following administration of Fosaprepitant for Injection. Examples birth control pills, skin patches, implants, and certain IUDs CYP2C9 Substrates Warfarin Clinical Impact Decreased warfarin exposure and decreased prothrombin time (INR) [see Warnings and Precautions (5.4), Clinical Pharmacology ( 12.3 )] .
Intervention In patients on chronic warfarin therapy, monitor the prothrombin time (INR) in the 2-week period, particularly at 7 to 10 days, following administration of Fosaprepitant for Injection with each chemotherapy cycle. Other 5-HT 3 Antagonists Clinical Impact No change in the exposure of the 5-HT 3 antagonist [see Clinical Pharmacology ( 12.3 )] . Intervention No dosage adjustment needed Examples ondansetron, granisetron, dolasetron
7.2Effect of Other Drugs on the Pharmacokinetics of Fosaprepitant/Aprepitant
Aprepitant is a CYP3A4 substrate [see Clinical Pharmacology ( 12.3 )] . Coadministration of Fosaprepitant for Injection with drugs that are inhibitors or inducers of CYP3A4 may result in increased or decreased plasma concentrations of aprepitant, respectively, as shown in Table 8. Table 8 Effects of Other Drugs on Pharmacokinetics of Fosaprepitant/Aprepitant Moderate to Strong CYP3A4 Inhibitors Clinical Impact Significantly increased exposure of aprepitant may increase the risk of adverse reactions associated with Fosaprepitant for Injection [see Adverse Reactions ( 6.1 ), Clinical Pharmacology ( 12.3 )] .
Intervention Avoid concomitant use of Fosaprepitant for Injection Examples Moderate inhibitor: diltiazem Strong inhibitors: ketoconazole, itraconazole, nefazodone, troleandomycin, clarithromycin, ritonavir, nelfinavir Strong CYP3A4 Inducers Clinical Impact Substantially decreased exposure of aprepitant in patients chronically taking a strong CYP3A4 inducer may decrease the efficacy of Fosaprepitant for Injection [see Clinical Pharmacology ( 12.3 )] .
Intervention Avoid concomitant use of Fosaprepitant for Injection Examples rifampin, carbamazepine, phenytoin