1 Introduction
Despite the development of targeted therapies and immunotherapies, chemotherapy remains a keystone of cancer treatment and is commonly used in combination with new treatment modalities [
1]. Patients receiving chemotherapy often experience chemotherapy-induced nausea and vomiting (CINV) [
2], which has a strong negative impact on their health-related quality of life [
3] and may lead to treatment delays or discontinuation [
4]. CINV can be divided into different subtypes depending on the time to symptom onset after administration of chemotherapy, including acute CINV, which occurs within the first 24 h of receiving chemotherapy [
5], and delayed CINV, which occurs 24 h after chemotherapy and may last up to 5 days [
6]. Real-world data suggest that the incidences of acute and delayed CINV are 55.3% and 62.3%, respectively, in Chinese patients with cancer receiving moderately emetogenic chemotherapy (MEC) or highly emetogenic chemotherapy (HEC) [
2]. Chow
et al. reported that long-delayed CINV (occurring 120–168 h after chemotherapy) affects a substantial number of patients and that the severity of long-delayed nausea is similar to that in the delayed phase; among patients receiving MEC, long-delayed nausea and vomiting occurred in 24% and 6%, respectively; among those receiving HEC, the proportions were 31% and 6%, respectively [
7]. Consistently, another Japanese multicenter prospective observational study showed that incidence rates of long-delayed nausea and vomiting were 22.2%–29.1% and 0%–6.7%, respectively [
8]. Therefore, optimal control of CINV is crucial in patients receiving chemotherapy.
Numerous antiemetic agents with different mechanisms of action are available for the treatment of CINV, with the primary options consisting of 5-hydroxytryptamine type 3 receptor antagonists (5-HT3RAs), neurokinin-1 receptor antagonists (NK1RAs), and corticosteroids [
9]. Considerable advances have been made in the management of acute CINV, with evidence that various antiemetic regimens can provide symptom control [
10]. However, in the control of delayed CINV, there are remaining challenges related to multiple factors including inherent treatment resistance of the delayed phase, inadequate prescribing of antiemetics, and patient non-adherence to medication [
6].
Guidelines for the management of CINV in clinical practice are available [
11]. One of the main considerations when choosing antiemetic strategies is the emetogenic potential of chemotherapy regimens, where minimal and low emetogenic risk chemotherapies cause CINV in < 10% and 10%–30% of patients, respectively, MEC in 30%–90% of patients, and HEC in > 90% [
12]. Generally, for prophylaxis of acute CINV in patients receiving MEC, a 5-HT3RA and dexamethasone with or without a NK1RA or olanzapine is recommended [
12]. For acute CINV in patients receiving HEC, the recommendation is typically at least a three-drug regimen including a NK1RA, a 5-HT3RA, and dexamethasone [
12]. Consensus on options for delayed CINV in patients receiving MEC or HEC is lacking across different guidelines [
12]. Documentation of CINV management guidelines in Asia-Pacific populations is limited, although available consensus recommendations are broadly aligned with Western guidelines [
13,
14].
The management of CINV could be improved by using an individualized approach that accounts not only for the emetogenic potential of chemotherapy regimens, but also patient-related risk factors for CINV as well as other therapy-related factors [
15]. Multiple-day chemotherapy regimens represent a particular challenge in the control of CINV, with difficulties in recommending specific antiemetic regimens due to the overlap between acute and delayed CINV after the first day of chemotherapy [
14,
16].
NK1RAs are approved for the prevention of acute and delayed CINV in adults receiving MEC or HEC [
17]. In this review, we summarize current data on the use of NK1RAs in the treatment of CINV, with a focus on evidence from China.
2 The emetic pathway and neurokinin-1 receptor
Both the peripheral and central nervous systems are involved in the pathophysiology of CINV, with different mechanisms responsible for the acute and delayed subtypes [
9,
18]. Acute CINV is primarily driven by the activation of peripheral nervous system pathways via 5-hydroxytryptamine (5-HT3) receptors [
19]. In contrast, delayed CINV is predominantly associated with a central mechanism involving the neurokinin-1 (NK1) receptor [
6,
9]. However, the CINV process is complex, with some evidence of signaling cross-talk between the 5-HT3 and NK1 pathways, although mechanistic details have not been fully elucidated [
9,
18]. Fig.1 shows the schematic of the emetic pathway.
The NK1 receptor is the primary receptor for the tachykinin family of peptides, which includes substance P [
20]. The NK1 receptor is distributed widely throughout human body including nervous, cardiovascular, genitourinary, and immune systems, as well as salivary glands, skin, and muscle [
20]. Consequently, the NK1 receptor is involved in a variety of processes including neuromodulation contributing to brain homeostasis; sensory neuronal transmission associated with depression, anxiety, stress, and vomiting; inflammatory response; and cellular responses such as pain transmission, endocrine and paracrine secretion, vasodilation, and cell proliferation [
20].
Since the NK1 receptor is implicated in multiple biological functions, it has become a target for the development of pharmaceutical interventions. NK1RAs, which represent a family of drugs that target the NK1 receptor to prevent the binding of substance P, have been studied for potential therapeutic applications in a variety of conditions including post-operative nausea and vomiting [
21] and CINV [
17,
22]. There is also evidence that NK1RAs may have antitumor activity in certain cancers [
23–
27].
3 Approved NK1RAs: formulations and indications
Tab.1 provides an overview of the five NK1RAs approved in the USA: aprepitant, fosaprepitant, netupitant, fosnetupitant, and rolapitant. NK1RAs are available as either oral or intravenous formulations, with the latter sometimes preferred for patients who have difficulty in swallowing capsules [
28]. Only aprepitant, fosaprepitant, and netupitant are currently available in China. Tab.1 also highlights differences in the formulations and indications that exist between the two countries.
Aprepitant was the first NK1RA to be approved, as an oral formulation given daily on the first 3 days of chemotherapy, in 2003 in the USA (capsules or suspension) and in 2014 in China (capsules only). Subsequently, the single-dose intravenous formulation was further approved in 2017 in the USA and in 2022 in China [
29]. The pharmacokinetics of aprepitant have been shown to be similar in Caucasian and Chinese populations [
30]. Fosaprepitant, a single-dose, intravenously administered NK1RA available in China and the USA, is a prodrug that is converted to aprepitant following administration [
28,
31]. The third NK1RA available in both China and the USA is netupitant, a single-dose, long-acting oral agent provided in fixed combination with the 5-HT3RA palonosetron (oral netupitant/palonosetron [NEPA]) [
32]. The fixed combination of fosnetupitant and palonosetron (intravenous NEPA) has also been introduced in the USA [
32,
33]. Both netupitant and palonosetron are long-acting drugs, synergistically improving the sustained antiemetic effect of NEPA throughout the chemotherapy cycle [
34]. Lastly, rolapitant, a single-dose, long-acting oral NK1RA, is available in the USA but not in China [
35].
4 Efficacy and safety of NK1RAs in CINV control
As the first NK1RA to be approved, aprepitant has the greatest amount of data supporting its efficacy and safety and is typically used as a comparator in phase III non-inferiority studies of other NK1RAs [
36–
39]. In phase III trials, aprepitant demonstrated efficacy in preventing both acute and delayed CINV regardless of the emetogenic risk of the chemotherapy [
36–
38,
40–
49]. Across milestone clinical trials in HEC, multiple-day dosing with aprepitant-based therapy was associated with complete control (no vomiting, no rescue medication) in 62.7%–89.2% of patients [
38]. Adding this NK1RA to the previous standard therapy of 5-HT3RA plus dexamethasone significantly increased the efficacy against CINV over multiple cycles of cisplatin chemotherapy, thus altering the standard of care for CINV [
38,
45,
50]. A pooled analysis of safety data across four pivotal clinical trials, including 1412 patients receiving HEC or MEC, showed that the most common adverse events with a higher incidence for aprepitant in combination with ondansetron and dexamethasone compared with ondansetron plus dexamethasone included fatigue (13% versus 12%), diarrhea (9% versus 8%), asthenia (7% versus 6%), dyspepsia (7% versus 5%), abdominal pain (6% versus 5%), hiccups (5% versus 3%), white blood cell count decreased (4% versus 3%), dehydration (3% versus 2%), and alanine aminotransferase increased (3% versus 2%) [
50].
Several phase III clinical trials have shown the superior efficacy of fosaprepitant compared with placebo [
51–
55] and non-inferior efficacy compared with aprepitant [
28,
38,
56,
57]. For example, in a randomized, controlled, phase III study including 2322 patients receiving cisplatin, the overall complete control rate was 71.9% with fosaprepitant plus ondansetron plus dexamethasone compared with 72.3% with aprepitant plus ondansetron plus dexamethasone [
57]. Complete control rates were also similar for both treatments in the delayed CINV phase from 25 to 120 h (74.3% versus 74.2%, respectively). Fosaprepitant has a similar safety profile to that of aprepitant [
28,
38,
56,
57]. For example, in the phase III study conducted in 2322 patients treated with cisplatin, the adverse event profile was generally consistent between the single-dose fosaprepitant-based and 3-day aprepitant-based triple regimens, although the fosaprepitant-based regimen was associated with a higher incidence of infusion site pain (1.4% versus 0.1%), erythema (0.5% versus 0.1%), and thrombophlebitis (0.8% and 0.7%), which may represent a barrier to its clinical use [
57].
Oral and intravenous NEPA also have phase III clinical data demonstrating non-inferior efficacy compared with aprepitant [
32,
58–
60]. Moreover, oral NEPA is associated with higher treatment compliance compared with aprepitant due to its convenient administration as a single tablet [
61]. Of note, phase III studies have shown that NEPA is effective in preventing delayed CINV, with the treatment effect maintained over several cycles of chemotherapy [
32,
58,
59,
62–
66]. Among 1862 patients receiving multiple cycles of HEC or MEC in two phase III trials, oral NEPA demonstrated a superior control rate compared with palonosetron alone in both acute and delayed CINV across multiple chemotherapy cycles [
66]. Complete control rates with NEPA ranged from 88.4% to 96.6% and 76.9% to 91.5% in the acute and delayed phases, respectively, across four chemotherapy cycles. Complete control rates with intravenous NEPA in phase III trials were similar to those reported with oral NEPA [
67]. In comparative clinical trials, (fos)netupitant showed a similar safety profile to aprepitant [
32,
35,
58,
60,
68], and safety profiles were consistent between fosnetupitant and netupitant [
64,
67]. In a phase III study of 834 patients from China and Thailand treated with HEC, the incidence of adverse events was similar for a single dose of NEPA plus dexamethasone versus a standard 3-day regimen of aprepitant plus granisetron plus dexamethasone (58.1% versus 57.5%), with the most common treatment-related adverse events being constipation (8.0% versus 6.3%) and hiccups (2.7% versus 1.4%) [
32]. Another phase III study in 795 patients receiving HEC reported that fosnetupitant or fosaprepitant, in combination with palonosetron plus dexamethasone, were associated with a similar incidences of treatment-related adverse events (22.2% versus 25.4%), as well as the most common adverse events of constipation (11.2% and 13.7%) and hiccups (4.8% and 7.1%) [
60].
Similarly, phase III trials showed that rolapitant effectively prevented delayed CINV, with benefits maintained over multiple cycles of chemotherapy [
35,
68–
72]. In a phase III study of 401 patients receiving MEC, rolapitant (day 1) was given in combination with granisetron (days 1–3) and dexamethasone (day 1). This rolapitant-based regimen was associated with a greater complete control rate compared with granisetron plus dexamethasone in both the overall (80.2% versus 64.6%) and delayed (82.3% versus 65.6%) phases [
69]. In 1087 patients receiving HEC in phase III studies, the complete control rate in the delayed phase was greater with rolapitant-based antiemetic prophylaxis versus granisetron plus dexamethasone alone (71% versus 60%) [
71]. Finally, in a pooled analysis of randomized phase II and phase III trials of rolapitant plus 5-HT3RA plus dexamethasone in which patients received multiple cycles of MEC or HEC, superior complete control rates versus 5-HT3RA (granisetron or ondansetron) plus dexamethasone were maintained for repeated antiemetic treatment for up to 6 cycles, with no cumulative toxicity [
70]. Compared with other oral NK1RAs, the most common treatment-related adverse events for rolapitant included constipation, fatigue, headache, hiccups and dyspepsia, while the incidence was low and similar to that of the active control group in phase III clinical studies [
68,
71,
72].
5 Administration modes of NK1RAs
In patients receiving HEC or MEC, dual or triple regimens are the standard therapy for preventing CINV [
73]. Clinical studies [
39,
41–
44,
74–
76] and systematic reviews [
36,
39,
77–
80] have shown that the addition of aprepitant to dexamethasone and 5-HT3RA is associated with a statistically significant and clinically relevant improvement in complete control rates in the prevention of CINV. For example, in a phase III study of 244 patients treated with cisplatin-based chemotherapy, adding aprepitant to palonosetron and dexamethasone improved complete control rates from 79.9% to 92.6% in the overall phase [
76]. It is recommended that the 5-HT3RA should be administered prior to the first (and subsequent) dose of MEC or HEC. The frequency or need for repeated administration of the 5-HT3RA depends on the agent chosen and the mode of administration (parenteral/oral/transdermal) [
73]. Although prophylactic dexamethasone has been generally considered safe, its administration may be associated with a wide range of side effects in the week after the initiation of chemotherapy [
81]. There is interest in minimizing the dose and frequency of dexamethasone use in antiemetic regimens, particularly in older patients and when combining immunotherapy with chemotherapy [
81–
88]. Dexamethasone-sparing strategies that limit dosing to only 1 day have been shown to maintain efficacy, although careful patient selection may be needed to ensure appropriate use of this approach [
83,
86].
Clinical evidence supporting the use of NK1RAs (aprepitant, fosaprepitant, netupitant, or rolapitant) in combination with 5-HT3RA and dexamethasone mainly focuses on the administration of the NK1RAs within the first 3 days of chemotherapy [
42,
43,
73,
89]. However, a small number of studies have explored extended administration of aprepitant up to day 7 after multiple-day chemotherapy [
43,
73,
90–
92]. For example, data from a randomized phase III study with a small sample size supported the use of aprepitant 125 mg on day 3 followed by 80 mg on days 4–7 as part of a triple regimen with 5-HT3RA on days 1–5 and dexamethasone on days 1 and 2 in 69 patients with germline malignancies treated with 5-day cisplatin-based chemotherapy [
43,
73]. Another randomized study with a small sample size found that prolonged administration of aprepitant for 6 days was associated with acceptable safety and encouraging efficacy in controlling CINV in patients treated with 3-day cisplatin-based chemotherapy [
92]. Further studies of extended aprepitant administration are warranted. However, studies investigating dosing of fosaprepitant, netupitant, and rolapitant beyond 3 days are not available [
73].
Several clinical studies have demonstrated the anti-emetic efficacy of NK1RA-based regimens in Chinese patients. For example, the addition of aprepitant to a standard anti-emetic regimen (granisetron and dexamethasone) improved CINV control in a phase III trial in 411 Chinese patients receiving HEC, with a complete control rate of 69.6% versus 57.0% overall, 74.0% versus 59.4% in the delayed phase, and 79.4% versus 79.3% in the acute phase, respectively [
44]. In another phase III trial, a single-dose fosaprepitant-based triplet regimen demonstrated non-inferior control of CINV compared with a standard 3-day aprepitant-based triplet regimen in 648 Chinese patients receiving HEC, with an overall complete control rate of 72.0% versus 69.4%, respectively [
93]. Similarly, in a prespecified analysis of a large subset of 672 Chinese patients receiving HEC in a phase III trial, a single dose of NEPA plus dexamethasone demonstrated similar efficacy in controlling CINV compared with a standard 3-day aprepitant plus granisetron plus dexamethasone regimen [
58]. For patients receiving NEPA plus dexamethasone versus the aprepitant-based regimen, no emesis was reported by 75.2% versus 75.6% of patients during days 1 to 5, 85.3% versus 88.1% in the acute phase, and 80.2% versus 77.4% in the delayed phase [
58]. A study in 645 Chinese patients receiving HEC also demonstrated that fosaprepitant plus granisetron plus dexamethasone was non-inferior to aprepitant plus granisetron plus dexamethasone therapy, with a complete control rate of 89.3% versus 92.7%, respectively [
28]. A randomized, double-blind, multicenter, phase III trial compared fosaprepitant injection (a Chinese domestically produced formulation) with aprepitant tablets, in combination with granisetron and dexamethasone, for the prevention of nausea and vomiting caused by HEC in 649 Chinese patients [
94]. This study showed fosaprepitant injection to be non-inferior to aprepitant in preventing CINV, with complete control of vomiting from 0 to 120 h after HEC in 79.3% versus 82.2% of patients, respectively. The two treatments also showed a similar safety profile [
94]. Finally, the addition of olanzapine 5 mg to triple anti-emetic therapy with fosaprepitant, ondansetron hydrochloride, and dexamethasone led to an increased control rate and was well tolerated in a phase III trial of Chinese patients receiving multiple-day cisplatin-based HEC [
95].
The use of multiple doses of fosaprepitant has been investigated and appears to provide a benefit in patients receiving multiple-day chemotherapy. For example, a multiple-dose regimen of fosaprepitant (on days 1 and 3) alongside palonosetron plus dexamethasone, compared with triple therapy comprising a single dose of fosaprepitant on day 1, led to a significantly lower rate of chemotherapy-induced nausea in the delayed phase and overall but not in the acute phase in 156 Chinese patients receiving HEC [
96]. The multiple-dosing approach was superior for controlling vomiting in the delayed phase but not in the overall or acute phases, and the incidence of adverse events for both approaches was comparable [
96]. In contrast, a phase III study of patients receiving 3-day cisplatin-based HEC showed that two doses of fosaprepitant on day 1 and 3 were superior to a single dose of fosaprepitant on day 1, when combined with oral palonosetron and oral dexamethasone, for controlling CINV in both the acute and delayed phases [
97]. No difference in adverse events was observed for the single and double fosaprepitant dose regimens.
6 Real-world evidence
Although randomized, controlled clinical trials have shown that NK1RAs are effective for the prevention of CINV, further real-world evidence is required to fully understand their application and effectiveness in routine clinical practice. Available real-world data from the USA and Europe supported the use of NK1RAs in the settings investigated during clinical development [
98–
102] and confirmed the cost-effectiveness of NK1RA-based therapy [
103]. Consistent findings have been reported from real-world studies in China [
94,
104,
105]. A post-marketing surveillance study conducted in 1000 Chinese patients across 21 centers showed that aprepitant was effective and safe, alone or in combination with other anti-emetic drugs, for preventing CINV associated with HEC [
104]. The rates of no vomiting and no nausea from 0 to 120 h were 71% and 43% with aprepitant monotherapy, 87% and 65% for aprepitant plus one other anti-emetic agent, and 86% and 70% for aprepitant plus two other anti-emetic agents. Only one patient experienced a drug-related serious adverse event, a gastrointestinal disorder that resolved during treatment. In a real-world study of 291 Chinese patients with lung cancer receiving cisplatin-based chemotherapy, the addition of aprepitant given as 125 mg on the first day of chemotherapy followed by 80 mg orally on the second and third days resulted in better control of nausea and vomiting compared with intravenous granisetron and oral dexamethasone alone (69% versus 57% in the acute phase and 72% versus 60% in the delayed phase) [
94]. Furthermore, a retrospective analysis of triple antiemetic agent regimens containing aprepitant for managing cisplatin-induced nausea and vomiting in 296 patients with melanoma reported a complete control rate of 84% and favorable tolerability [
105].
However, compliance with antiemetic guidelines tends to be low, as demonstrated by a large prospective registry study in Eastern Europe where only 23% of patients were receiving guideline-consistent CINV prophylaxis [
106]. Similarly, a study conducted in Sichuan, China, reported that only 21.5% (239/1110) of patients were managed in-line with local guidelines; 27.1% of patients receiving MEC and 4.6% receiving HEC [
2]. Moreover, NK1RAs appeared to be under-used in routine clinical practice [
106,
107]. Understanding the reasons for low levels of guideline adherence among healthcare providers (HCPs) could help improve outcomes for patients, given that patients consider CINV as one of the most distressing side effects of chemotherapy [
98,
106,
108,
109]. Delayed CINV is often underestimated by Chinese HCPs, which may contribute to the under-use of NK1RAs in China [
110]. In addition to sub-optimal implementation of guidelines by HCPs, patient factors may play a role in non-adherence to CINV prophylaxis. For example, patients may face challenges to follow antiemetic regimens as prescribed, especially during home administration [
98,
99]. A survey of European oncologists showed that approximately one third of patients made administration mistakes or missed/delayed at least one dose during home administration of antiemetics [
111]. The complexity of the antiemetic regimen can also impact adherence and simplified antiemetic regimens may improve CNIV control [
111]. With the exception of oral aprepitant, which is administered on the first 3 days of chemotherapy, NK1RAs require only single administration on day 1, reducing the need for home treatment and improving patient compliance with antiemetic regimens [
22]. Moreover, NK1RAs are available in different formulations, which can be matched to patient preference [
22].
Further research is needed to determine the optimal use of NK1RAs, identify patient populations who may gain the greatest benefit from NK1RA therapy, and understand patient preferences and unmet needs in this setting. A CINV predictive model has undergone real-word validation and optimization for identifying Chinese patients who are at high risk of CINV, which may aid in physicians’ decisions on CINV prevention [
112].
7 Conclusions and clinical perspective
The development and approval of NK1RAs has significantly improved CINV management in patients receiving HEC or MEC. These agents have generally favorable safety profiles and efficacy in the prevention of both acute and delayed CINV. The use of these antiemetic drugs has improved management of CINV and resulted in a significant decrease in the incidence and severity of CINV. However, while these agents generally have favorable safety profiles, they can cause side effects such as fatigue, constipation, and hiccups. When choosing an antiemetic agent, it is critical to consider comorbidities and chemotherapy regimens. Further research is needed to determine the best way to use these agents and to identify strategies to manage CINV in specific patient populations, such as those with gastrointestinal disorders.