A Randomized, Double-blind, Two-stage, Placebo-controlled Phase 2b/3 Clinical Study to Evaluate the Efficacy and Safety of Ziresovir (AK0529) in Adult Patients at High Risk for Respiratory Syncytial Virus (RSV) Infection.

Respiratory syncytial virus (RSV) is recognized worldwide as a significant pathogen causing lower respiratory tract infection in infants, the elderly, and immunocompromised patients, which may cause bronchiolitis or pneumonia, and affect the cardiovascular system, central nervous system and the renal system, resulting in hospitalization and death risks in children and also high-risk adults, particularly the elderly. The purpose of this study is to evaluate the efficacy of Ziresovir (AK0529) compared to placebo with respect to the time to resolution of RSV lower respiratory tract disease (LRTD) symptoms.

Start Date03 Mar 2026

Sponsor / Collaborator

Shanghai Ark Biopharmaceutical Co., Ltd.

NCT06591845

/ CompletedPhase 1

A Single-Center, Randomized, Partially Double-Blind, Placebo- and Active-Controlled, Four-period Crossover, Thorough QT/QTc (TQT) Clinical Study to Evaluate the Effects of Ziresovir on Cardiac Repolarization in Healthy Subjects

This is a single-center, randomized, partially double-blind, placebo and active-controlled, 4-period crossover design thorough QT/QTc (TQT) clinical study to evaluate the effects of ziresovir on cardiac repolarization in healthy subjects.

Start Date25 Sep 2024

Sponsor / Collaborator

Shanghai Ark Biopharmaceutical Co., Ltd.

NCT06775405

/ RecruitingPhase 3

A Randomized, Double-blind, Placebo-controlled, Phase III Confirmatory Study to Evaluate the Efficacy, Safety, Tolerability, and Antiviral Activity of Repeated Oral Administration of AK0529 in Hospitalized Infants with Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is the most common respiratory infectious pathogen recognized worldwide that poses serious health risks to infants, and an important cause of hospitalization for severe respiratory infections in infants. Serious respiratory problems such as pneumonia caused by RSV are one of the leading causes of death from respiratory diseases in infants. AK0529 targets the Pre-F (fusion) protein on the surface of the viral envelope. Specifically, it prevents the virus from invading uninfected cells and inhibits the fusion between host cells by inhibiting the fusion of the F (fusion) proteins on the surface of the RSV envelope, thus providing the effects of anti-RSV infection. This is a randomized, double-blind, placebo-controlled, multicenter, phase III clinical study to evaluate the efficacy and safety of AK0529 in hospitalized infants aged 1 to 24 months with RSV infection. Considering the benefits of AK0529 in the population with RSV infection, hospitalized infants with moderate to severe RSV infection were selected as the target population for this study.

Start Date29 Feb 2024

Sponsor / Collaborator

Shanghai Ark Biopharmaceutical Co., Ltd.

100 Clinical Results associated with Ziresovir

100 Translational Medicine associated with Ziresovir

100 Patents (Medical) associated with Ziresovir

Literatures (Medical) associated with Ziresovir

01 Jun 2026·LIFE SCIENCES

Broad-spectrum coronavirus inhibition by RSV fusion inhibitors targeting six-helix bundle formation

Article

Author: Go, Yun Young ; Chen, Weiyi ; Shin, Jin Soo ; Chen, Zhenhai ; Yeh, Jung-Yong ; Zhou, Bin ; Jung, Eunhye ; Ji, Min Chae

Waning vaccine-derived immunity and the emergence of new SARS-CoV-2 subvariants continue to challenge global public health, emphasizing the need for novel inhibitors against SARS-CoV-2 infection. Molecular inhibitors targeting virus entry are promising candidates as they can disrupt viral replication at the earliest stage. In this study, we utilized a fluorescence-based SARS-CoV-2 pseudovirus screening platform to identify entry inhibitors from a repurposed library of bioactive compounds. Ziresovir and TMC353121, both small molecules known as respiratory syncytial virus (RSV) fusion inhibitors, were identified as hits that inhibited SARS-CoV-2 pseudovirus entry. In vitro and in silico analyses, together with site-directed mutagenesis, demonstrated that these molecules interfere with the formation of the six-helix bundle (6HB) in the SARS-CoV-2 spike (S) protein, thereby inhibiting membrane fusion. Additionally, both compounds exhibited inhibitory effects against SARS-CoV pseudovirus, wild-type SARS-CoV-2, and several other coronaviruses. These findings identify Ziresovir and TMC353121 as mechanistically validated scaffolds that target conserved fusion mechanisms across different viral families. While further optimization is required to enhance their potency against infectious SARS-CoV-2, this study provides a strategic foundation and chemical templates for the development of broad-spectrum fusion inhibitors to combat current and future coronavirus threats.

01 Feb 2026·RESPIRATORY MEDICINE

Respiratory syncytial virus in high-risk adults: A critical appraisal of therapeutic options and unmet needs

Review

Author: Ranellou, Kyriaki ; Panagiotopoulos, Antonios-Periklis ; Anastassopoulou, Cleo ; Mariolis, Ilias ; Tsakris, Athanasios

Respiratory syncytial virus (RSV) has traditionally been viewed as a causative agent of pediatric illness, yet accumulating evidence shows substantial morbidity and mortality among adults, particularly older individuals, those with cardiopulmonary comorbidities, and the immunocompromised. Although recent vaccine approvals for older adults represent major progress in prevention, effective therapeutic options for established infection remain limited. Herein we provide a critical analysis of existing and emerging antiviral and monoclonal antibody (mAb) therapies for the management of RSV infection in adults, highlighting current options and compounds in clinical development. At present, ribavirin remains the only antiviral recommended for treatment in adults, and no mAb has received regulatory authorization for prophylaxis or therapy in this population. Several development programs for direct-acting antivirals have been discontinued for reasons unrelated to safety or efficacy in adults, contributing to an ongoing treatment gap. Nevertheless, newer drug candidates, including ziresovir, EDP-938, and S-337395, have shown encouraging antiviral activity and acceptable safety in adult studies. By examining both the scientific evidence and the structural factors shaping the current landscape, we emphasize the need for sustained adult-focused clinical development to complement preventive vaccination. Addressing this therapeutic gap will be essential to reduce the burden of RSV disease in high-risk adult populations, particularly as the global population ages.

02 Dec 2025·Expert Opinion on Drug Discovery

Synthetic oxetanes in drug discovery: where are we in 2025?

Review

Author: Bull, James A. ; Ishikura, Hikaru

INTRODUCTION:

Oxetanes are increasingly prevalent motifs in medicinal chemistry. While oxetanes feature famously in the taxol family, it was not until the recent approval of rilzabrutinib that they have been validated in a fully synthetic drug. These four-membered oxygen-containing rings are valued for their ability to modulate key physicochemical properties such as polarity, lipophilicity, and metabolic stability. Their incorporation can improve aqueous solubility, reduce metabolic liability, reduce basicity of adjacent amines, and redirect metabolic clearance away from cytochrome P450 enzymes.

AREAS COVERED:

This review examines the role of the oxetane in nine clinical candidates, one very recently approved, two recently discontinued clinical candidates, two tool compounds, and three lead compounds disclosed in 2024. Recent advances indexed in SciFinder-n (2017-2024) in the process-scale and laboratory-scale synthetic routes are discussed, highlighting ongoing innovation required to access these motifs efficiently and sustainably.

EXPERT OPINION:

The regulatory approval of rilzabrutinib and likely approval of ziresovir provide confidence in using oxetanes as important elements in drug design. While oxetanes have so far been incorporated primarily as pendant groups to optimize physicochemical properties, their use as scaffolding and binding elements presents an exciting opportunity. Enhanced synthetic accessibility to oxetane derivatives will expedite their inclusion in drug discovery campaigns.

News (Medical) associated with Ziresovir

20 Apr 2026

·allsci.com

EC approves Merck’s Enflonsia for RSV prevention in infants

The European Commission has approved Enflonsia (clesrovimab) for the prevention of RSV lower respiratory tract disease in neonates and infants during their first RSV season. Merck noted that the product is the first RSV preventive option in the European Union not requiring weight-based dosing. The authorization covers all 27 EU member states as well as Iceland, Liechtenstein, and Norway, and adds to prior approvals in the US, Canada, and Switzerland. The EC authorization permits a fixed 105 mg intramuscular dose regardless of infant weight, designed to provide protection across five months — the duration of a typical RSV season. For infants born during the RSV season, the label specifies administration within the first week of life; for those born outside the season, dosing should occur shortly before it begins. Infants undergoing cardiac surgery with cardiopulmonary bypass are recommended an additional 105 mg dose once stable post-surgery. The product carries a contraindication for infants with hypersensitivity to clesrovimab or its excipients, and Merck said the timing of country-level availability will depend on completion of reimbursement procedures. The approval is supported by data from two trials. The pivotal Phase IIb/III CLEVER trial (NCT04767373) enrolled 3,614 preterm and full-term infants randomized 2:1 to a single 105 mg dose of clesrovimab or saline placebo. The primary endpoint — incidence of RSV-associated medically attended lower respiratory infection through 150 days — was reduced by 60.4% versus placebo (95% CI: 44.1, 71.9; p<0.001). RSV-associated hospitalization through five months, the key secondary endpoint, was reduced by 84.2% (95% CI: 66.6, 92.6; p<0.001). Exploratory analyses showed a 91.7% reduction in severe medically attended lower respiratory infection and a 90.9% reduction in RSV-associated lower respiratory tract hospitalization over the same period. The safety profile was comparable to placebo, with the most frequent adverse reactions being injection-site pain (6.5%), injection-site erythema (4.4%), injection-site swelling (3.2%), and rash (2.3%), the majority mild or moderate. Supporting data came from an interim analysis of the Phase III SMART trial (NCT04938830), which compared clesrovimab against monthly palivizumab in 896 infants at increased risk for severe RSV disease. Incidence rates of medically attended lower respiratory infection and hospitalization were comparable between the two arms, with efficacy in the high-risk population established by pharmacokinetic extrapolation from the CLEVER trial. Results from both studies were published in the New England Journal of Medicine in September 2025. The RSV market context RSV is among the leading causes of infant hospitalization globally, capable of progressing to bronchiolitis and pneumonia in both healthy and high-risk infants. Until recently, prophylaxis options were limited largely to palivizumab (Synagis; AstraZeneca), a monthly weight-based injection restricted in most health systems to high-risk populations due to cost and dosing burden. The 2023 approval of nirsevimab (Beyfortus; AstraZeneca/Sanofi) broadened access to a single-season, single-dose option for all infants, and clesrovimab now joins that class with a fixed-dose presentation that Merck said eliminates the need for weight-based calculation at the point of care. The clesrovimab EC approval adds to a growing field of long-acting monoclonal antibodies for infant RSV prophylaxis, with the fixed-dose feature representing a practical distinction from palivizumab and a potential implementation consideration for healthcare systems evaluating uptake. The CLEVER and SMART data also indicate that the antibody maintains activity in high-risk subgroups — including preterm infants and those with chronic lung disease or congenital heart disease — populations where the historical standard of care had been palivizumab administered monthly across the season. The broader RSV prevention and treatment landscape continues to evolve. Pfizer’s maternal RSV vaccine Abrysvo received FDA approval for maternal immunization in 2023, offering an alternative route to infant protection via transplacental antibody transfer, and Moderna’s mRNA-1345 maternal immunization program remains in Phase III investigation. Both approaches, if widely adopted, could affect demand for prophylactic monoclonal antibodies across the infant population. On the treatment side, no antiviral is approved for RSV in infants; investigational agents including ziresovir (Ark Biosciences) and sisunatovir (Pfizer) are in Phase II/III and Phase II evaluation respectively for RSV lower respiratory tract infection treatment in hospitalized infants, a niche that prophylactic antibodies do not address. Merck itself is pursuing MK-5348, an RSV polymerase inhibitor, in Phase I/II for treatment indications, positioning the company across both the preventive and potential therapeutic segments of the RSV space. Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website

10 Apr 2026

·www.prnewswire.com

ArkBio Completed Dosing of First Cohort in Australian Phase I Trial of Antiviral Drug-Fc Conjugate Drug AK0406

SHANGHAI, April 9, 2026 /PRNewswire/ -- Shanghai Ark Biopharmaceutical Co., Ltd. ("ArkBio") today announced that the first cohort of healthy volunteers has been dosed in a phase I clinical trial of AK0406, a novel long-acting antiviral drug-Fc conjugate (ADFC) drug for influenza infection, following approval by the Human Research Ethics Committee (HREC) in Australia. This milestone marks the first-in-human (FIH) evaluation of AK0406 and an important step in the global clinical development of ArkBio's influenza pipeline. AK0406 is a next-generation, long-acting ADFC candidate discovered and developed by ArkBio. By conjugating a potent small-molecule antiviral to the antibody Fc domain, AK0406 is designed to combine the direct antiviral effect of the payload with Fc-mediated immune clearance and an extended half-life. Preclinical data show that AK0406 exerts broad-spectrum, high-potency activity against both influenza A and B viruses, maintains immune effector function, and provides prolonged exposure. Compared with first-generation ADFC molecules, AK0406 is engineered to offer an optimized profile for both prophylaxis and treatment of influenza infection. The phase I trial is a single-center, randomized, double-blind, placebo-controlled study designed to assess the safety, tolerability, and pharmacokinetic (PK) profile of AK0406 in healthy adult participants in Australia. Data from this FIH study will inform subsequent dose selection and future proof-of-concept trials in populations at risk for influenza infection. Influenza remains a significant global public health burden, causing substantial morbidity and mortality each year and posing an ongoing pandemic threat. Current preventive measures, including seasonal vaccination, are challenged by antigenic drift, strain-selection uncertainty, and reduced effectiveness in the general population, especially in vulnerable groups such as older adults and immunocompromised individuals. With its long-acting, broad-spectrum ADFC design, AK0406 has the potential to address key limitations of existing therapies and offer improved options for both prevention and treatment of seasonal influenza and potential pandemic outbreaks. ArkBio will continue to accelerate the clinical development of AK0406 and work with global partners to advance better prevention and treatment options for patients worldwide. About ArkBio ArkBio is a commercial-stage biotechnology company focused on the discovery and development of innovative therapeutics for respiratory/lung and pediatric diseases. Founded in 2014, the company has established proprietary technology platforms and a differentiated R&D pipeline through internal innovation and strategic collaborations. Key pipeline assets include: ziresovir (AK0529), the first direct-acting antiviral for RSV with positive pivotal phase 3 results; AK3280, a potentially best-in-class anti-fibrotic agent with positive phase 2 results in idiopathic pulmonary fibrosis and is advancing into Phase 3 registrational trials; AK0901, approved and commercialized in China for the treatment of ADHD. The company also has multiple first-in-class or best-in-class innovative candidates in clinical or preclinical development. ArkBio has established strategic partnerships with multinational pharmaceutical companies including Roche and Genentech, leading academic institutions such as The Scripps Research Institute and the Institute of Microbiology of the Chinese Academy of Sciences, Qilu Pharmaceutical as well as other domestic and international biotech companies and CROs. For more information, please visit: Investor Inquiries: [email protected] SOURCE Arkbio 21% more press release views with Request a Demo

Phase 1Phase 3Drug ApprovalClinical ResultImmunotherapy

12 Feb 2026

·www.prnewswire.com

Novel Anti-Fibrotic Drug AK3280 Cleared by FDA to Initiate Phase 2 Proof-of-Concept Clinical Trial in IPF

SHANGHAI, Feb. 11, 2026 /PRNewswire/ -- Shanghai Ark Biopharmaceutical Co., Ltd. ("ArkBio") today announced that the U.S. Food and Drug Administration (FDA) has cleared its Investigational New Drug (IND) application for AK3280, a novel anti-fibrotic therapy for the treatment of idiopathic pulmonary fibrosis (IPF). This clearance enables ArkBio to initiate a Phase 2 proof-of-concept (PoC) clinical trial of AK3280 in the United States. The Phase 2 study is a multi-center, randomized, partially double-blind, placebo- and active-controlled trial designed to evaluate the efficacy, safety, and pharmacokinetics of oral AK3280 in patients with IPF. Authorization to proceed with a U.S. Phase 2 study represents a significant milestone in the global clinical development of AK3280. IPF is a progressive, irreversible, and ultimately fatal interstitial lung disease characterized by fibrotic remodeling of lung tissue that leads to respiratory failure. The median survival following diagnosis is approximately 2–5 years. Currently approved therapies, including pirfenidone, nintedanib, and nerandomilast, can slow disease progression; however, their clinical benefit remains limited and they are frequently associated with gastrointestinal adverse events such as diarrhea and nausea. These tolerability challenges contribute to poor long-term adherence in a substantial proportion of patients. There remains a significant unmet need for therapies that provide improved efficacy with enhanced safety and tolerability profiles. AK3280 is an optimized, small-molecule, broad-spectrum anti-fibrotic agent. In a Phase 2 proof-of-concept study conducted in China, AK3280 demonstrated encouraging clinical activity, including a statistically significant, dose-dependent absolute increase from baseline in forced vital capacity (FVC) at Week 24. Improvements were also observed across additional lung function parameters, suggesting meaningful clinical benefit. Importantly, AK3280 exhibited a favorable safety and tolerability profile, with no apparent increase in the gastrointestinal adverse effects commonly associated with currently available IPF therapies. FDA clearance of the IND marks a pivotal step in the global development of AK3280. The upcoming international Phase 2 PoC trial is expected to generate critical clinical data to support future regulatory submissions and potential commercialization in the United States and other major markets. ArkBio remains committed to advancing AK3280 globally and to delivering more effective and better-tolerated treatment options for patients living with IPF. About ArkBio ArkBio is a commercial-stage biotechnology company focused on the discovery and development of innovative therapeutics for respiratory and pediatric diseases. Founded in 2014, the company has established proprietary technology platforms and a differentiated R&D pipeline through internal innovation and strategic collaborations. Key pipeline assets include: Ziresovir (AK0529), the first direct-acting antiviral for RSV with positive pivotal Phase 3 results; AK3280, a potentially best-in-class anti-fibrotic agent with positive Phase 2 results in idiopathic pulmonary fibrosis; AK0901, approved in China for the treatment of ADHD and currently commercialized. ArkBio has established strategic partnerships with multinational pharmaceutical companies and leading academic institutions, including Roche, Genentech, The Scripps Research Institute, and the Institute of Microbiology of the Chinese Academy of Sciences, as well as domestic and international biotech companies and venture capital partners. For more information, please visit: Investor Inquiries: [email protected] SOURCE Arkbio 21% more press release views with Request a Demo

Phase 2INDPhase 3Drug ApprovalClinical Result

100 Deals associated with Ziresovir

External Link

KEGG	Wiki	ATC	Drug Bank
-	Ziresovir	-	DB15145

R&D Status

10 top R&D records.

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Indication	Highest Phase	Country/Location	Organization	Date
Respiratory Syncytial Virus Infections	NDA/BLA	China	Shanghai Ark Biopharmaceutical Co., Ltd.	08 Dec 2022

Clinical Result

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Evaluation

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Study	Phase	Population	Analyzed Enrollment	Group	Results	Evaluation	Publication Date


NCT04231968 (Pubmed \| NEWS) Manual	Phase 3	Respiratory Syncytial Virus Infections	188	ziresovir	avzpglwysc(uhbjdkexyo) = kcjhvqgypi ismjhcbxdm (lizdxycvsr, -3.9 to -3.1) View more	Positive	01 May 2025
				Placebo	avzpglwysc(uhbjdkexyo) = wnqsgqjbdu ismjhcbxdm (lizdxycvsr, -2.8 to -1.7) View more
NCT04231968 (AIRFLO, Pubmed \| N Engl J Med)	Phase 3	Respiratory Syncytial Virus Infections	244	Ziresovir	yxgxjegwmo(mfupbaotjh) = Resistance-associated mutations were identified in 15 participants (9%) in the ziresovir group ikbaivcoha (dztfgdnpwm ) View more	Positive	26 Sep 2024
				Placebo
NCT04231968 (AIRFLO, Literature) Manual	Phase 3	Respiratory Syncytial Virus Infections	302	Ziresovir	tmnbiadctp(plpnzcqvxm) = nkndoqnwpb aeuewwntmq (mxhecpprwd, −3.7 - −3.1) View more	Positive	25 Sep 2024
				Placebo	tmnbiadctp(plpnzcqvxm) = vfhvamader aeuewwntmq (mxhecpprwd, −3.1 - −2.2) View more

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