Prevention of Post COVID-19 Condition by Early Treatment with Ensitrelvir in the Phase 3 SCORPIO-SR Trial.

This exploratory analysis of the double-blind, phase 3, SCORPIO-SR trial assessed the effect of ensitrelvir in preventing post coronavirus disease 2019 (COVID-19) condition (PCC). Patients with mild-to-moderate COVID-19 were randomized (1:1:1) within 120 hours of symptom onset; received 5-day oral ensitrelvir 125 mg (375 mg on day 1), 250 mg (750 mg on day 1), or a matching placebo once daily; and were assessed for the severity of typical PCC symptoms using a self-administered questionnaire. In total, 341, 317, and 333 patients were assessed in the ensitrelvir 125-mg, ensitrelvir 250-mg, and placebo groups, respectively (mean age, 35.6-36.5 years; men, 53.3%-58.3%). On days 85, 169, and 337, ensitrelvir 125-mg treatment showed 32.7% (95% confidence interval [CI]: -30.6, 66.1), 21.5% (95% CI: -37.3, 55.6), and 24.6% (95% CI: -43.7, 60.9) reductions versus placebo, respectively, in the risk of any of the 14 acute-phase COVID-19 symptoms (at least one mild, moderate, or severe symptom with general health not returning to the usual level). Ensitrelvir 250-mg treatment showed 10.9% (95% CI: -67.0, 52.8), 9.5% (95% CI: -56.6, 48.0), and 30.6% (95% CI: -36.2, 65.5) risk reductions versus placebo on days 85, 169, and 337, respectively. Risk reductions were observed in any of the 4 neurological symptoms and were more pronounced among patients with high acute-phase symptom scores at baseline and among those with a baseline body mass index ≥25 kg/m2. Ensitrelvir treatment in the acute phase of COVID-19 may reduce the risk of various symptoms associated with PCC. TRIAL REGISTRATION NUMBER: jRCT2031210350.

Real-World Effectiveness of Ensitrelvir in Reducing Severe Outcomes in Outpatients at High Risk for COVID-19.

INTRODUCTION: This study aimed to evaluate the effectiveness of ensitrelvir, an oral antiviral, in reducing hospitalization risk in outpatients at high-risk for severe COVID-19 during the Omicron era. METHODS: This was a retrospective study using a large Japanese health insurance claims database. It included high-risk outpatients for severe symptoms who received their first COVID-19 diagnosis between November 2022 and July 2023. The study included outpatients aged ≥ 18 years. The primary endpoint was all-cause hospitalization during the 4-week period from the date of outpatient diagnosis and medication, comparing the ensitrelvir group (n = 5177) and the no antiviral treatment group (n = 162,133). The risk ratio and risk difference were evaluated after adjusting patient background distribution by the inverse probability of treatment weight (IPTW) method. Secondary endpoints were incidence of respiratory and heart rate monitoring, oxygen therapy, ventilator use, intensive care admission, and all-cause death. RESULTS: The risk ratio for all-cause hospitalization between the ensitrelvir group (n = 167,385) and the no antiviral treatment group (n = 167,310) after IPTW adjustment was 0.629 [95% confidence interval (CI) 0.420, 0.943]. The risk difference was - 0.291 [95% CI - 0.494, - 0.088]. The incidence of both respiratory and heart rate monitoring and oxygen therapy was lower in the ensitrelvir group. Ventilator use, intensive care admission, and all-cause death were difficult to assess because of the limited events. CONCLUSIONS: The incidence of all-cause hospitalization was significantly lower in the ensitrelvir group than in the no antiviral treatment group, suggesting ensitrelvir is an effective treatment in patients at risk of severe COVID-19.

COVID-19 still poses a risk for patients with serious health conditions and weakened immune systems, who are more likely to develop severe illness. Several studies have indicated that some oral antiviral medications might be effective in preventing severe disease. This study aimed to evaluate if ensitrelvir, an oral antiviral medication, can help prevent hospitalization in outpatients who are at risk of developing severe symptoms from the Omicron variant of the SARS-CoV-2 virus. The hospitalization rates of patients who received ensitrelvir was compared with those who did not receive any antiviral treatment, using medical records from a large health insurance database in Japan focused on outpatients who were at risk of severe symptoms and were diagnosed with COVID-19 between November 2022 and July 2023. Respiratory and heart rate monitoring, oxygen therapy, ventilator use, intensive care admission, and all-cause death were also evaluated. The study found that patients who received ensitrelvir had a lower risk of being hospitalized compared to those who did not receive any antiviral treatment. The ensitrelvir group also had lower rates of respiratory and heart rate monitoring and oxygen therapy. However, it was challenging to assess the effects on ventilator use, intensive care admission, and all-cause death due to the small number of events in the population under evaluation. Based on these findings, ensitrelvir appears to be an effective treatment for reducing the risk of hospitalization in patients at risk of severe COVID-19.

Efficacy and Safety of Ensitrelvir for Asymptomatic or Mild COVID-19: An Exploratory Analysis of a Multicenter, Randomized, Phase 2b/3 Clinical Trial.

BACKGROUND: This phase 2b/3, randomized, placebo-controlled trial explored the efficacy and evaluated the safety of ensitrelvir. This trial involved individuals with asymptomatic infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and patients with mild symptoms of coronavirus disease 2019 (COVID-19). METHODS: The trial was conducted at 57 medical institutions in Japan, South Korea, and Vietnam (study period: January 6-August 14, 2022). Eligible participants were randomized (1:1:1) to the ensitrelvir 125-mg, ensitrelvir 250-mg, or placebo group, received the allocated intervention orally, and were followed up until Day 28. Participants self-rated the severity of 14 typical COVID-19 symptoms and recorded the data in an electronic diary. RESULTS: In total, 572 participants (194, 189, and 189 in the ensitrelvir 125-mg, ensitrelvir 250-mg, and placebo groups, respectively) were included in the intention-to-treat population. Ensitrelvir 125-mg group observed a 77% reduction in the risk of developing any of the 14 COVID-19 symptoms or fever and a 29% reduction in the risk of worsening of such symptoms or fever versus placebo (statistically nonsignificant). The viral RNA, viral titer, and time to infectious viral clearance observed a statistically significant decrease versus placebo. Most treatment-related adverse events (TEAEs) were mild to moderate in severity, and the most common TEAE observed across groups was a decrease in high-density lipoprotein. CONCLUSIONS: Our exploratory results suggest a potential reduction in the risk of development or worsening of COVID-19 symptoms with ensitrelvir. Ensitrelvir showed antiviral efficacy and was well tolerated. TRIAL REGISTRATION: Japan Registry of Clinical Trials identifier: jRCT2031210350.

Efficacy and Safety of 5-Day Oral Ensitrelvir for Patients With Mild to Moderate COVID-19: The SCORPIO-SR Randomized Clinical Trial.

Importance: Treatment options for COVID-19 are warranted irrespective of the presence of risk factors for severe disease. Objective: To assess the efficacy and safety of ensitrelvir in patients with mild to moderate COVID-19. Design, Setting, and Participants: This phase 3 part of a phase 2/3, double-blind, placebo-controlled randomized clinical trial was conducted from February 10 to July 10, 2022, with a 28-day follow-up period, at 92 institutions in Japan, Vietnam, and South Korea. Patients (aged 12 to <70 years) with mild to moderate COVID-19 within 120 hours of positive viral test results were studied. Interventions: Patients were randomized (1:1:1) to receive 125 mg of once-daily ensitrelvir (375 mg on day 1), 250 mg of once-daily ensitrelvir (750 mg on day 1), or placebo for 5 days. Main Outcomes and Measures: The primary end point was the time to resolution of the composite of 5 characteristic symptoms of SARS-CoV-2 Omicron infection, assessed using a Peto-Prentice generalized Wilcoxon test stratified by vaccination history. Virologic efficacy and safety were also assessed. Results: A total of 1821 patients were randomized, of whom 1030 (347 in the 125-mg ensitrelvir group, 340 in the 250-mg ensitrelvir group, and 343 in the placebo group) were randomized in less than 72 hours of disease onset (primary analysis population). The mean (SD) age in this population was 35.2 (12.3) years, and 552 (53.6%) were men. A significant difference was observed between the 125-mg ensitrelvir group and the placebo group (P = .04 with a Peto-Prentice generalized Wilcoxon test). The difference in median time was approximately 1 day between the 125-mg ensitrelvir group and the placebo group (167.9 vs 192.2 hours; difference, -24.3 hours; 95% CI, -78.7 to 11.7 hours). Adverse events were observed in 267 of 604 patients (44.2%) in the 125-mg ensitrelvir group, 321 of 599 patients (53.6%) in the 250-mg ensitrelvir group, and 150 of 605 patients (24.8%) in the placebo group, which included a decrease in high-density lipoprotein level (188 [31.1%] in the 125-mg ensitrelvir group, 231 [38.6%] in the 250-mg ensitrelvir group, and 23 [3.8%] in the placebo group). No treatment-related serious adverse events were reported. Conclusions and Relevance: In this randomized clinical trial, 125-mg ensitrelvir treatment reduced the time to resolution of the 5 typical COVID-19 symptoms compared with placebo in patients treated in less than 72 hours of disease onset; the absolute difference in median time to resolution was approximately 1 day. Ensitrelvir demonstrated clinical and antiviral efficacy without new safety concerns. Generalizability to populations outside Asia should be confirmed. Trial Registration: Japan Registry of Clinical Trials Identifier: jRCT2031210350.

A phase 2/3 study of S-217622 in participants with SARS-CoV-2 infection (Phase 3 part).

BACKGROUND: Limited treatment options exist for patients with mild-to-moderate coronavirus disease 2019 (COVID-19), irrespective of vaccination history or risk status. Ensitrelvir is a novel oral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3C-like (3CL) protease inhibitor. While phase 2 studies of ensitrelvir have demonstrated promising results in treating mild-to-moderate COVID-19, evaluation of its clinical efficacy due to shifting vaccination status and emergence of the Omicron variant represents significant challenges. Here, we describe the protocol for a phase 3 study designed to evaluate the efficacy and safety of ensitrelvir in patients with mild-to-moderate COVID-19, regardless of risk status or vaccination history. METHODS: This is a multicenter, randomized, double-blind, placebo-controlled, phase 3 study. Patients with mild-to-moderate COVID-19 within 120 hours from onset will be randomized in a 1:1:1 ratio into 3 treatment arms-ensitrelvir 125 mg (375 mg loading dose on Day 1), ensitrelvir 250 mg (750 mg loading dose on Day 1), and placebo. The study interventions will be administered orally, once-daily, for 5 days. The primary endpoint will be the time to resolution of 5 symptoms of COVID-19 (stuffy or runny nose, sore throat, cough, feeling hot or feverish, and low energy or tiredness), and the key secondary endpoints will include the change from baseline on Day 4 in the amount of SARS-CoV-2 viral ribonucleic acid (RNA) and the time to first negative SARS-CoV-2 viral titer. The primary population for the primary and key secondary endpoints will be patients with <72 hours from COVID-19 onset to randomization and, subsequently, patients in entire patient population (<120 hours) in the ensitrelvir 125 mg group. Closed testing procedure will be used for the primary and key secondary endpoints in both the primary and entire patient populations. All safety assessments and adverse events (AE) will be reported. DISCUSSION: In a post hoc analysis of the phase 2b study, compared with placebo, ensitrelvir demonstrated a reduced time to resolution of 5 symptoms in patients with mild-to-moderate COVID-19. Through this study, we intend to validate and establish the efficacy and safety of ensitrelvir in patients with mild-to-moderate COVID-19.

Investigating the transmission of baloxavir-resistant influenza viruses from treated index patients to untreated household contacts in the BLOCKSTONE study.

In a post-hoc analysis of the phase 3 BLOCKSTONE study (JapicCTI-184180), we investigated household transmission of baloxavir-resistant (PA/I38X) influenza viruses. Using baloxavir resistance rates from prior clinical trials and the rate of influenza transmission observed in the study, the predicted number of PA/I38X transmission events was 4.8, assuming wild type and PA/I38X viruses were equally transmissible. However, no PA/I38X viruses were observed. These results suggest a low potential for baloxavir-resistant influenza virus transmission from treated to untreated individuals, potentially due to reduced viral/transmission fitness for PA/I38X viruses and/or low viral titres at the time when resistant viruses arise.

Baloxavir safety and clinical and virologic outcomes in influenza virus-infected pediatric patients by age group: age-based pooled analysis of two pediatric studies conducted in Japan.

BACKGROUND: Anti-influenza treatment is important for children and is recommended in many countries. This study assessed safety, clinical, and virologic outcomes of baloxavir marboxil (baloxavir) treatment in children based on age and influenza virus type/subtype. METHODS: This was a post hoc pooled analysis of two open-label non-controlled studies of a single weight-based oral dose of baloxavir (day 1) in influenza virus-infected Japanese patients aged < 6 years (n = 56) and ≥ 6 to < 12 years (n = 81). Safety, time to illness alleviation (TTIA), time to resolution of fever (TTRF), recurrence of influenza illness symptoms and fever (after day 4), virus titer, and outcomes by polymerase acidic protein variants at position I38 (PA/I38X) were evaluated. RESULTS: Adverse events were reported in 39.0 and 39.5% of patients < 6 years and ≥ 6 to < 12 years, respectively. Median (95% confidence interval) TTIA was 43.2 (36.3-68.4) and 45.4 (38.9-61.0) hours, and TTRF was 32.2 (26.8-37.8) and 20.7 (19.2-23.8) hours, for patients < 6 years and ≥ 6 to < 12 years, respectively. Symptom and fever recurrence was more common in patients < 6 years with influenza B (54.5 and 50.0%, respectively) compared with older patients (0 and 25.0%, respectively). Virus titers declined (day 2) for both age groups. Transient virus titer increase and PA/I38X-variants were more common for patients < 6 years. CONCLUSIONS: The safety and effectiveness of single-dose baloxavir were observed in children across all age groups and influenza virus types. Higher rates of fever recurrence and transient virus titer increase were observed in children < 6 years. TRIAL REGISTRATION: Japan Pharmaceutical Information Center Clinical Trials Information JapicCTI-163,417 (registered 02 November 2016) and JapicCTI-173,811 (registered 15 December 2017).

Efficacy and Safety of Ensitrelvir in Patients With Mild-to-Moderate Coronavirus Disease 2019: The Phase 2b Part of a Randomized, Placebo-Controlled, Phase 2/3 Study.

BACKGROUND: This phase 2b part of a randomized phase 2/3 study assessed the efficacy and safety of ensitrelvir for mild-to-moderate coronavirus disease 2019 (COVID-19) during the Omicron epidemic. METHODS: Patients were randomized (1:1:1) to orally receive ensitrelvir fumaric acid 125 mg (375 mg on day 1) or 250 mg (750 mg on day 1) or placebo once daily for 5 days. The co-primary endpoints were the change from baseline in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) titer on day 4 and time-weighted average change from baseline up to 120 hours in the total score of predefined 12 COVID-19 symptoms. Safety was assessed through adverse events. RESULTS: A total of 341 patients (ensitrelvir 125-mg group: 114; ensitrelvir 250-mg group: 116; and placebo group: 111; male: 53.5-64.9%; mean age: 35.3-37.3 years) were included in the efficacy analyses. The change from baseline in SARS-CoV-2 titer on day 4 was significantly greater with both ensitrelvir doses than with placebo (differences from placebo: -0.41 log10 50% tissue-culture infectious dose/mL; P < .0001 for both). The total score of the 12 COVID-19 symptoms did not show a significant difference between the ensitrelvir groups and placebo group. The time-weighted average change from baseline up to 120 hours was significantly greater with ensitrelvir versus placebo in several subtotal scores, including acute symptoms and respiratory symptoms. Most adverse events were mild in severity. CONCLUSIONS: Ensitrelvir treatment demonstrated a favorable antiviral efficacy and potential clinical benefit with an acceptable safety profile. CLINICAL TRIALS REGISTRATION: Japan Registry of Clinical Trials: jRCT2031210350 (https://jrct.niph.go.jp/en-latest-detail/jRCT2031210350).

A Randomized Phase 2/3 Study of Ensitrelvir, a Novel Oral SARS-CoV-2 3C-Like Protease Inhibitor, in Japanese Patients with Mild-to-Moderate COVID-19 or Asymptomatic SARS-CoV-2 Infection: Results of the Phase 2a Part.

This multicenter, double-blind, phase 2a part of a phase 2/3 study assessed the efficacy and safety of ensitrelvir, a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3C-like protease inhibitor, in Japanese patients with mild-to-moderate coronavirus disease 2019 (COVID-19) or asymptomatic SARS-CoV-2 infection. Sixty-nine patients were randomized (1:1:1) to orally receive 5-day ensitrelvir fumaric acid (375 mg on day 1 followed by 125 mg daily, or 750 mg on day 1 followed by 250 mg daily) or placebo and followed up until day 28. The primary outcome was the change from baseline in the SARS-CoV-2 viral titer. A total of 16, 14, and 17 patients in the ensitrelvir 125 mg, ensitrelvir 250 mg, and placebo groups, respectively, were included in the intention-to-treat population (mean age: 38.0 to 40.4 years). On day 4, the change from baseline in SARS-CoV-2 viral titer (log10 50% tissue culture infectious dose/mL) in patients with positive viral titer and viral RNA at baseline was greater with ensitrelvir 125 mg (mean [standard deviation], -2.42 [1.42]; P = 0.0712) and 250 mg (-2.81 [1.21]; P = 0.0083) versus placebo (-1.54 [0.74]); ensitrelvir treatment reduced SARS-CoV-2 RNA by -1.4 to -1.5 log10 copies/mL versus placebo. The viral titer and viral RNA were similar across groups on and after day 6. The median time to infectious viral clearance decreased by approximately 50 h with ensitrelvir treatment. All adverse events were mild to moderate. Ensitrelvir treatment demonstrated rapid SARS-CoV-2 clearance and was well tolerated (Japan Registry of Clinical Trials identifier: jRCT2031210350).

The DEN and CCl4 -Induced Mouse Model of Fibrosis and Inflammation-Associated Hepatocellular Carcinoma.

Human hepatocellular carcinoma (HCC) develops most often as a complication of fibrosis or cirrhosis. Although most human studies of HCC provide crucial insights into the molecular signatures of HCC, they seldom address its etiology. Mouse models provide essential tools for investigating the pathogenesis of HCC, but the majority of rodent cancer models do not feature liver fibrosis. Detailed here is a protocol for an experimental mouse model of HCC that arises in association with advanced liver fibrosis. The disease model is induced by a single injection of N-nitrosodiethylamine (DEN) at 2 weeks of age followed by repeated administration of carbon tetrachloride (CCl4 ) from 8 weeks of age for up to 14 consecutive weeks. A dramatic potentiation of liver tumor incidence is observed following administration of DEN and CCl4 , with 100% of mice developing liver tumors at 5 months of age. This model has been employed for studying the molecular mechanisms of fibrogenesis and HCC development, as well as for cancer hazard/chemotherapy testing of drug candidates. © 2021 Wiley Periodicals LLC. Basic Protocol: The DEN and CCl4 -induced mouse model of fibrosis and inflammation-associated hepatocellular carcinoma.

Open-label study of the safety, pharmacokinetics, and effectiveness of a 2 mg/kg dose of baloxavir marboxil 2% granules in children <20 kg with influenza.

INTRODUCTION: Baloxavir marboxil is an oral anti-influenza drug with demonstrated safety and efficacy in pediatric patients when a 2% granules formulation is administered at 1 mg/kg. This study assessed safety, effectiveness, and pharmacokinetics of a higher dose (2 mg/kg) of baloxavir marboxil 2% granules in pediatric patients weighing <20 kg. METHODS: This multicenter, open-label, noncontrolled study was conducted at 15 sites in Japan (January 2019-March 2020; JapicCTI-194577). Patients aged <12 years with confirmed influenza received a single oral dose of baloxavir marboxil at 2 mg/kg if body weight was <10 kg or 20 mg if ≥ 10 to <20 kg. Safety, pharmacokinetics, effectiveness (time to illness alleviation [TTIA] of influenza; time to resolution of fever; virus titer), and polymerase acidic protein (PA) substituted viruses were assessed over 22 days. RESULTS: 45 patients, all aged ≤6 years, were enrolled. Adverse events were reported in 24 (53.3%) patients, most commonly nasopharyngitis, diarrhea, and upper respiratory tract infection. Median (95% confidence interval [CI]) TTIA was 37.8 (27.5-46.7) hours; median (95% CI) time to resolution of fever was 22.0 (20.2-28.6) hours. A >4 log decrease in mean viral titer occurred at day 2 and a subsequent temporary 1-2 log increase in patients with influenza A(H3N2) and B. Treatment-emergent PA/I38X-substituted virus was detected in 16/39 (41.0%) patients, but no prolonged TTIA or time to resolution of fever was associated with its presence. CONCLUSIONS: Baloxavir granules administered at 2 mg/kg in children <20 kg were well tolerated, with symptom alleviation similar to 1 mg/kg.

Evaluating the fitness of PA/I38T-substituted influenza A viruses with reduced baloxavir susceptibility in a competitive mixtures ferret model.

Baloxavir is approved in several countries for the treatment of uncomplicated influenza in otherwise-healthy and high-risk patients. Treatment-emergent viruses with reduced susceptibility to baloxavir have been detected in clinical trials, but the likelihood of widespread occurrence depends on replication capacity and onward transmission. We evaluated the fitness of A/H3N2 and A/H1N1pdm09 viruses with the polymerase acidic (PA) I38T-variant conferring reduced susceptibility to baloxavir relative to wild-type (WT) viruses, using a competitive mixture ferret model, recombinant viruses and patient-derived virus isolates. The A/H3N2 PA/I38T virus showed a reduction in within-host fitness but comparable between-host fitness to the WT virus, while the A/H1N1pdm09 PA/I38T virus had broadly similar within-host fitness but substantially lower between-host fitness. Although PA/I38T viruses replicate and transmit between ferrets, our data suggest that viruses with this amino acid substitution have lower fitness relative to WT and this relative fitness cost was greater in A/H1N1pdm09 viruses than in A/H3N2 viruses.

Baloxavir Treatment in Adolescents With Acute Influenza: Subgroup Analysis From the CAPSTONE-1 Trial.

BACKGROUND: Baloxavir marboxil has demonstrated safety and efficacy in treating adult and adolescent outpatients with acute influenza (CAPSTONE-1 trial). Here, we report a subgroup analysis of outcomes in adolescents from the trial. METHODS: CAPSTONE-1 was a randomized, double-blind, placebo-controlled study. Eligible adolescent outpatients (aged 12-17 years of age) were randomized in a ratio of 2:1 to a single dose of baloxavir 40/80 mg if less than/greater than or equal to 80 kg or placebo. The main outcomes were the time to alleviation of symptoms (TTAS), duration of infectious virus detection, and incidence of adverse events (AEs). RESULTS: Among 117 adolescent patients, 90 (77%) comprised the intent-to-treat infected population (63 baloxavir and 27 placebo; 88.9% A(H3N2)). The median TTAS was 38.6 hours shorter (95% confidence interval: -2.6, 68.4) in the baloxavir group compared with placebo (median TTAS, 54.1 hours vs 92.7 hours, P = .0055). The median time to sustained cessation of infectious virus detection was 72.0 hours for baloxavir compared with 120.0 hours for placebo recipients (P < .0001). Treatment-emergent PA/I38X-substituted viruses were detected in 5 of the 51 (9.8%) baloxavir recipients. In the safety population (76 baloxavir and 41 placebo), AEs were less common in baloxavir than placebo recipients (17.1% vs 34.1%; P = .0421). In the baloxavir group, no AEs except for diarrhea were reported in 2 or more patients. CONCLUSIONS: Baloxavir demonstrated clinical and virologic efficacy in the otherwise healthy adolescents with acute influenza compared with placebo. There were no safety concerns identified. These results were similar to the adult population in CAPSTONE-1 and support baloxavir as a treatment option in adolescents.

Baloxavir Marboxil for Prophylaxis against Influenza in Household Contacts.

BACKGROUND: Baloxavir marboxil (baloxavir) is a polymerase acidic protein (PA) endonuclease inhibitor with clinical efficacy in the treatment of uncomplicated influenza, including in outpatients at increased risk for complications. The postexposure prophylactic efficacy of baloxavir in the household setting is unclear. METHODS: We conducted a multicenter, double-blind, randomized, placebo-controlled trial to evaluate the postexposure prophylactic efficacy of baloxavir in household contacts of index patients with confirmed influenza during the 2018-2019 season in Japan. The participants were assigned in a 1:1 ratio to receive either a single dose of baloxavir or placebo. The primary end point was clinical influenza, as confirmed by reverse-transcriptase-polymerase-chain-reaction testing, over a period of 10 days. The occurrence of baloxavir-selected PA substitutions associated with reduced susceptibility was assessed. RESULTS: A total of 752 household contacts of 545 index patients were randomly assigned to receive baloxavir or placebo. Among the index patients, 95.6% had influenza A virus infection, 73.6% were younger than 12 years of age, and 52.7% received baloxavir. Among the participants who could be evaluated (374 in the baloxavir group and 375 in the placebo group), the percentage in whom clinical influenza developed was significantly lower in the baloxavir group than in the placebo group (1.9% vs. 13.6%) (adjusted risk ratio, 0.14; 95% confidence interval [CI], 0.06 to 0.30; P<0.001). Baloxavir was effective in high-risk, pediatric, and unvaccinated subgroups of participants. The risk of influenza infection, regardless of symptoms, was lower with baloxavir than with placebo (adjusted risk ratio, 0.43; 95% CI, 0.32 to 0.58). The incidence of adverse events was similar in the two groups (22.2% in the baloxavir group and 20.5% in the placebo group). In the baloxavir group, the viral PA substitutions I38T/M or E23K were detected in 10 (2.7%) and 5 (1.3%) participants, respectively. No transmission of these variants from baloxavir-treated index patients to participants in the placebo group was detected; however, several instances of transmission to participants in the baloxavir group could not be ruled out. CONCLUSIONS: Single-dose baloxavir showed significant postexposure prophylactic efficacy in preventing influenza in household contacts of patients with influenza. (Funded by Shionogi; Japan Primary Registries Network number, JapicCTI-184180.).

Early treatment with baloxavir marboxil in high-risk adolescent and adult outpatients with uncomplicated influenza (CAPSTONE-2): a randomised, placebo-controlled, phase 3 trial.

BACKGROUND: Baloxavir marboxil (hereafter baloxavir), a selective inhibitor of influenza cap-dependent endonuclease, was approved in 2018 in the USA and Japan for the treatment of uncomplicated influenza in otherwise healthy individuals aged 12 years and older. We aimed to study the efficacy of baloxavir in outpatients at high risk of developing influenza-associated complications. METHODS: We did a double-blind, placebo-controlled and oseltamivir-controlled trial in outpatients aged 12 years and older in 551 sites in 17 countries and territories. Eligible patients had clinically diagnosed influenza-like illness, at least one risk factor for influenza-associated complications (eg, age older than 65 years), and a symptom duration of less than 48 h. Patients were stratified by baseline symptom score (≤14 vs ≥15), pre-existing and worsened symptoms at onset of illness compared with pre-influenza (yes or no), region (Asia, North America and Europe, or southern hemisphere), and weight (<80 kg vs ≥80 kg), and randomly assigned (1:1:1) via an interactive web-response system to either a single weight-based dose of baloxavir (40 mg for patients weighing <80 kg and 80 mg for patients weighing ≥80 kg; baloxavir group), oseltamivir 75 mg twice daily for 5 days (oseltamivir group), or matching placebo (placebo group). All patients, investigators, study personnel, and data analysts were masked to treatment assignment until database lock. The primary endpoint was time to improvement of influenza symptoms (TTIIS) in the modified intention-to-treat population, which included all patients who received at least one dose of study drug and had RT-PCR-confirmed influenza virus infection. Safety was assessed in all patients who receved at least one dose of study drug. This trial is registered with ClinicalTrials.gov, NCT02949011. FINDINGS: 2184 patients were enrolled from Jan 11, 2017, to March 30, 2018, and randomly assigned to receive baloxavir (n=730), placebo (n=729), or oseltamivir (n=725). The modified intention-to-treat population included 1163 patients: 388 in the baloxavir group, 386 in the placebo group, and 389 in the oseltamivir group. 557 (48%) of 1163 patients had influenza A H3N2, 484 (42%) had influenza B, 80 (7%) had influenza A H1N1, 14 patients had a mixed infection, and 28 had infections with non-typable viruses. The median TTIIS was shorter in the baloxavir group (73·2 h [95% CI 67·2 to 85·1]) than in the placebo group (102·3 h [92·7 to 113·1]; difference 29·1 h [95% CI 14·6 to 42·8]; p<0·0001). The median TTIIS in the oseltamivir group was 81·0 h (95% CI 69·4 to 91·5), with a difference from the baloxavir group of 7·7 h (-7·9 to 22·7). Adverse events were reported in 183 (25%) of 730 patients in the baloxavir group, 216 (30%) of 727 in the placebo group, and 202 (28%) of 721 in the oseltamivir group. Serious adverse events were noted in five patients in the baloxavir group, nine patients in the placebo group, and eight patients in the oseltamivir group; one case each of hypertension and nausea in the placebo group and two cases of transaminase elevation in the oseltamivir group were considered to be treatment related. Polymerase acidic protein variants with Ile38Thr, Ile38Met, or Ile38Asn substitutions conferring reduced baloxavir susceptibility emerged in 15 (5%) of 290 baloxavir recipients assessed for amino acid substitutions in the virus. INTERPRETATION: Single-dose baloxavir has superior efficacy to placebo and similar efficacy to oseltamivir for ameliorating influenza symptoms in high-risk outpatients. The safety of baloxavir was comparable to placebo. This study supports early therapy for patients at high risk of complications of influenza to speed clinical recovery and reduce complications. FUNDING: Shionogi.

Baloxavir Marboxil 2% Granules in Japanese Children With Influenza: An Open-label Phase 3 Study.

BACKGROUND: A granule formulation of baloxavir marboxil, a selective inhibitor of influenza cap-dependent endonuclease, was newly developed for children with difficulty swallowing tablets. METHODS: A multicenter open-label study was conducted during the 2017-2018 influenza season to assess the safety, pharmacokinetics and clinical/virologic outcomes of single, oral, weight-based doses of baloxavir granules in Japanese children infected with influenza virus. The primary clinical endpoint was the time to illness alleviation of influenza. RESULTS: All 33 enrolled children completed the study and received baloxavir (1 mg/kg for 12 children weighing <10 kg, 10 mg for 21 children weighing 10 to <20 kg). Detected viruses were influenza B (36.4%), A(H1N1)pdm09 (33.3%) and A(H3N2) (27.3%). Adverse events (AEs) were reported in 54.5% of children. No deaths, serious AEs or AEs leading to discontinuation were reported. The mean (SD) plasma concentrations of baloxavir acid at 24 hours post-dose were 72.8 (24.0) and 51.3 (19.3) ng/mL in the 1-mg/kg and 10-mg dose groups, respectively. The median time to illness alleviation (95% confidence interval) was 45.3 (28.5-64.1) hours. A >4-log decrease in infectious viral titer occurred on day 2 and a temporary 2-log increase on day 4. Polymerase acidic protein/I38T/M-substituted viruses were detected in 5 children infected with influenza A, but none with influenza B. CONCLUSIONS: Baloxavir granules and the weight-based dose regimen were considered to be well tolerated in children, with rapid influenza virus reduction and associated symptom alleviation. Evidence of baloxavir activity against influenza B was observed, but further data are required for confirmation.

Baloxavir treatment of ferrets infected with influenza A(H1N1)pdm09 virus reduces onward transmission.

Influenza viruses cause seasonal outbreaks and pose a continuous pandemic threat. Although vaccines are available for influenza control, their efficacy varies each season and a vaccine for a novel pandemic virus manufactured using current technology will not be available fast enough to mitigate the effect of the first pandemic wave. Antivirals can be effective against many different influenza viruses but have not thus far been used extensively for outbreak control. Baloxavir, a recently licensed antiviral drug that targets the influenza virus endonuclease, has been shown to reduce virus shedding more effectively than oseltamivir, a widely used neuraminidase inhibitor drug. Thus it is possible that treatment with baloxavir might also interrupt onward virus transmission. To test this, we utilized the ferret model, which is the most commonly used animal model to study influenza virus transmission. We established a subcutaneous baloxavir administration method in ferrets which achieved similar pharmacokinetics to the approved human oral dose. Transmission studies were then conducted in two different locations with different experimental setups to compare the onward transmission of A(H1N1)pdm09 virus from infected ferrets treated with baloxavir, oseltamivir or placebo to naïve sentinel ferrets exposed either indirectly in adjacent cages or directly by co-housing. We found that baloxavir treatment reduced infectious viral shedding in the upper respiratory tract of ferrets compared to placebo, and reduced the frequency of transmission amongst sentinels in both experimental setups, even when treatment was delayed until 2 days post-infection. In contrast, oseltamivir treatment did not substantially affect viral shedding or transmission compared to placebo. We did not detect the emergence of baloxavir-resistant variants in treated animals or in untreated sentinels. Our results support the concept that antivirals which decrease viral shedding could also reduce influenza transmission in the community.

Carryover effects of baloxavir acid in human nasopharyngeal/pharyngeal swabs on infectious titer testing of influenza virus.

Baloxavir marboxil (BXM) demonstrated a rapid and profound decline in infectious viral titer 1 day after BXM administration. Rapid reduction in virus titer is a characteristic of BXM. There may be a possibility that drug carryover effects have impacts on the observed antiviral effects due to the poor correlation that was observed between viral titer reduction and alleviation of influenza symptoms. Here, we report possible carryover effects of baloxavir acid (BXA), an active form of BXM, on infectious titer testing. Our findings indicate that there is little impact of BXA carryover on the infectious titer testing.

Baloxavir Marboxil in Japanese Pediatric Patients With Influenza: Safety and Clinical and Virologic Outcomes.

BACKGROUND: We assessed the safety and effectiveness of baloxavir marboxil administration in Japanese children with influenza. METHODS: This open-label study administered 1 weight-adjusted dose of baloxavir to 107 children aged 1-11 years with laboratory-confirmed, febrile influenza virus infection of ≤48 hours duration. RESULTS: Adverse events (AEs) were reported in 34.6% of patients, most commonly vomiting (7.5%); no serious AEs or AEs causing discontinuation occurred. The median time to alleviation of influenza illness was 44.6 hours (95% confidence interval, 38.9-62.5 hours), to resolution of fever was 21.4 hours, and to sustained cessation of infectious viral shedding was 24.0 hours. However, viruses with amino acid substitutions in the viral polymerase acidic protein at position I38 (PA/I38T/M) emerged in 18 of 77 (23.4%) patients. Emergence was associated with longer infectious virus detectability (median time, 180.0 hours) and time to illness alleviation (median, 79.6 vs 42.8 hours in patients without PA/I38T/M-substituted viruses). Among patients with PA/I38T/M-substituted virus emergence, those with baseline hemagglutinin inhibition (HAI) antibody titer <40 experienced delay in time to illness alleviation (median, 85.4 vs 56.0 hours in patients with higher baseline HAI antibody titer). CONCLUSIONS: A single, oral dose of baloxavir marboxil was well tolerated and rapidly reduced viral titers, but the common emergence of PA/I38T/M-substituted viruses warrants consideration of alternative dosing regimens in young children. CLINICAL TRIALS REGISTRATION: Japan Pharmaceutical Information Center Clinical Trials Information (Japic CTI-163417).