Background: Fosnetupitant (FN) is a phosphorylated pro-drug of netupitant that has high binding affinity for the neurokinin-1 (NK-1) receptor and a long half-life of 70 h. This phase 3 study is the first head-to-head study to compare two NK-1 receptor antagonists, FN and fosaprepitant (FA), in combination with palonosetron and dexamethasone for the prevention of chemotherapy-induced nausea and vomiting (CINV) in patients receiving highly emetogenic chemotherapy (JapicCTI-194611). Methods: Patients scheduled to receive cisplatin (≥70 mg/m²) -based chemotherapy were randomly assigned 1:1 to receive FN 235 mg or FA 150 mg, in combination with palonosetron 0.75 mg and dexamethasone (9.9 mg on day 1, 6.6 mg on days 2-4). The stratification factors were sex, age category (<55 vs. ≥55 years), and site. The primary endpoint was the complete response (CR; no emetic events and no rescue medication) rate, stratified by sex and age category, during the overall phase (0-120 h) to show the non-inferiority (margin, -10%) of FN to FA. The secondary endpoints were: CR rate, complete protection rate, total control rate, no nausea rate, no emetic events rate in each period [i.e., acute (0-24 h), delayed (24-120 h), overall, 0-168 h and 120-168 h], time to treatment failure, and safety, including injection site reactions (ISRs). Assessment of efficacy was continued until 168 h after the initiation of cisplatin. Some eligible patients were evaluated for safety and efficacy of FN for up to four cycles. Results: Between February 2019 and March 2020, total 795 patients were enrolled in the study. The study drug was administered to 785 patients (n=392 in FN vs. n=393 in FA), and all of them were evaluated for efficacy and safety. Baseline characteristics were generally balanced between the two groups. The adjusted overall CR rate was 75.2% in FN vs. 71.0% in FA [MH common risk difference, 4.1%; 95% CI, -2.1% to 10.3%), thus demonstrating non-inferiority of FN to FA. Regarding the other secondary endpoints of efficacy until 168 h, FN was favorable against FA, especially the CR rate during 0-168 h (73.2% in FN vs. 66.9% in FA) (Table). The incidence rates of treatment-related adverse events were 22.2% in FN vs. 25.4% in FA, whereas those of ISRs with any cause or with treatment-related were 11.0% or 0.3% in FN vs 20.6% or 3.6% in FA, respectively (p<0.001). Conclusions: FN demonstrated non-inferiority to FA, with a favorable safety profile and lower risk for ISRs. For the period beyond 120 h after initiation of chemotherapy, FN may have the potential to improve the prevention of “beyond delayed” CINV. Clinical trial information: JapicCTI-194611.

* Stratified by sex and age category.