Effect of aprepitant (AP) on cyclophosphamide (CPA) pharmacokinetics (PK) in early breast cancer patients

Abstract

588 Background: AP, a moderate inhibitor of CYP3A4, is a selective neurokinin 1 receptor antagonist recommended by the ASCO guidelines for prevention of high and some moderately emetogenic chemotherapy regimens, including doxorubicin and CPA (AC). CPA is converted to the active 4-OH metabolite primarily by CYP2B6 (48–57%) and by CYP3A4 (12–18%). CYP3A4 also converts 10% of CPA to the N-dechloroethyl metabolite (DCE), which is responsible for neurotoxicity and nephrotoxicity. Because AP is utilized concurrently with CPA, this creates the potential for drug-drug interaction between AP and CPA. The objective of this study was to evaluate the effect of AP on the PK of CPA, 4-OH, and DCE in patients receiving AC. Methods: This double-blinded, placebo controlled, two-period, crossover study included breast cancer patients receiving regimens containing CPA 600 mg/m2 IV for at least two sequential cycles. Prior to each CPA cycle, patients were randomized to receive either oral AP (125 mg on d 1 prior to chemotherapy and 80 mg on d 2 and 3) or placebo for 3 d. During both cycles, patients were also pretreated with ondansetron 24 mg PO and dex 12 mg PO on d 1 and dex 8 mg PO once on d 2 and 3. Rescue anti-emetic medications were permitted. Serial plasma samples were obtained from 0 to 24 h after administration of CPA in combination with AP or placebo in each patient. CPA, 4-OH, and DCE plasma concentrations were determined using HPLC. Area under the plasma versus conc time curve (AUC) was calculated using WinNonlin. Results: 17 patients completed 2 cycles and were evaluated for PK. Geometric mean AUC data for CPA in combination with AP and placebo are summarized in the table. Conclusions: Based on geometric mean ratios ± 90% CI, concurrent administration of AP with CPA did not result in any significant changes in the 4-OH metabolite AUC, but did result in increased parent CPA and decreased DCE drug exposure levels. Based on these results, it is unlikely that aprepitant has a clinically significant effect on the efficacy of CPA. [Table: see text] [Table: see text]