A Study to Learn About the Amount of the Study Medicine (Sisunatovir) in Blood and Its Safety in Infants and Children With Pneumonia Caused by RSV

AN INTERVENTIONAL, PHASE 1b, RANDOMIZED, DOUBLE-BLIND, SPONSOR-OPEN, PLACEBO-CONTROLLED, MULTI-CENTER, DOSE-FINDING STUDY TO EVALUATE SAFETY, TOLERABILITY AND PHARMACOKINETICS OF SISUNATOVIR IN PEDIATRIC PARTICIPANTS UP TO AGE 60 MONTHS WITH RESPIRATORY SYNCYTIAL VIRUS (RSV) LOWER RESPIRATORY TRACT INFECTION (LRTI)

The purpose of the study is to learn about the safety and amount of sisunatovir in the blood of infants and children up to age 60 months. These children have Lower Respiratory Tract Infection (LRTI) caused by Respiratory Syncytial Virus (RSV). LRTI is the infection to the lower airways such as lungs.

This study will help inform the amount of sisunatovir to be used in future studies of sisunatovir in children.

This study is seeking for participants who:

• Are 1 day to less than or equal to 60 months of age
• weigh more than or equal to 2.5 kilograms to less than or equal to 23 kilograms.
• Have been tested to have RSV by medical tests.
• show signs of LRTI.

All participants in the study will receive many amounts of sisunatovir or placebo. Placebo is a pill that does not have any medicine in it.

Up to 7 visits are required for the study. Some of these visits include checking participants health over the phone and/or a visit at home.

The study will compare the experiences of infants and children receiving sisunatovir to identify the amount of sisunatovir to be used in future studies in infants and children.

Study Overview

• Status: Terminated
• Conditions: Respiratory Syncytial Virus Infections
• Intervention / Treatment: Drug: Placebo; Drug: Active

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Phase 1

Contacts and Locations

Study Locations

• Japan
  • Osaka, Japan, 534-0021
    • Osaka City General Hospital
  • Aichi-ken
    • Nagoya, Aichi-ken, Japan, 457-8511
      • Kojunkai Daido Hospital
  • Kagoshima-ken
    • Hioki, Kagoshima-ken, Japan, 899-2503
      • Nintenkai Kagoshima Children's Hospital
  • Yamanashi
    • Kofu, Yamanashi, Japan, 400-8506
      • Yamanashi Prefectural Central Hospital
• South Africa
  • Eastern Cape
    • Mdantsane, Eastern Cape, South Africa, 5219
      • Monti Clinical Research Centre
  • Gauteng
    • Johannesburg, Gauteng, South Africa, 2013
      • University of Witwatersrand (WITS) - Vaccines and Infectious Diseases Analytics (VIDA)
• United States
  • California
    • Los Angeles, California, United States, 90027
      • Kaiser Permanente Los Angeles Medical Center
    • Los Angeles, California, United States, 90027
      • Kaiser Permanente
  • Missouri
    • St Louis, Missouri, United States, 63110
      • Washington University School of Medicine

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• 1 day to ≤60 months of age and weight ≥2.5 kg to ≤23 kg
• Positive RSV diagnostic test, antigen or molecular test
• Evidence of Lower Respiratory Tract Infection (LRTI)

Exclusion Criteria:

• Premature infants (gestational age less than 35 weeks) AND <1 year of post-natal age
• Neonates with intrauterine growth restriction
• Expected to receive an antiviral for another viral infection within 10 days of screening
• Suspected or confirmed clinically significant moderate or severe bacterial infection that may interfere with the evaluation of response to the study intervention
• Known to have significant comorbidities that would limit the ability to administer the study intervention or evaluate the safety or clinical response to the study intervention

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Placebo Comparator: Placebo; Oral or Nasogastric tube (NG)	Drug: Placebo; Placebo
Active Comparator: Sisunatovir; Oral or NG tube	Drug: Active; Sisunatovir; Other Names: PF-07923568, RV521

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Number of Participants With Treatment Emergent Adverse Events (TEAEs)	An adverse event (AE) was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE was considered a TEAE if the event started during the effective duration of treatment. All events that start on or after the first dose of study intervention, but before the end of the study were flagged as TEAEs. All AEs were included for evaluation.	From start of study intervention on Day 1 up to 28 days after last dose of study intervention (maximum up to 33 days)
Number of Participants Who Discontinued From Study Due to TEAEs	An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE was considered a TEAE if the event started during the effective duration of treatment. All events that start on or after the first dose of study intervention, but before the end of the study were flagged as TEAEs.	From start of study intervention on Day 1 up to 28 days after last dose of study intervention (maximum up to 33 days)
Number of Participants Who Discontinued From Study Due to Serious TEAEs	An AE was any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE was considered a TEAE if the event started during the effective duration of treatment. All events that start on or after the first dose of study intervention, but before the end of the study were flagged as TEAEs. A serious AE (SAE) was any untoward medical occurrence at any dose that: resulted in death; was life-threatening experience (immediate risk of death); required inpatient hospitalization or prolongation if existing hospitalization; resulted in persistent or significant disability/ incapacity; resulted in congenital anomaly/birth defect; other important event or situation as pre-specified in protocol.	From start of study intervention on Day 1 up to 28 days after last dose of study intervention (maximum up to 33 days)
Number of Participants With Clinically Significant Laboratory Abnormalities	Following parameters were analyzed for laboratory examination: hematology (hemoglobin, hematocrit, red blood cell count, platelet count, white blood cell count, mean cell volume, mean cell hemoglobin & concentration); chemistry: urea and creatinine, estimated glomerular filtration rate (eGFR), gamma-glutamyl transferase (GGT), calcium, sodium, potassium, chloride, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin, alkaline phosphatase, albumin, total protein, cystatin C; urinalysis: pH, glucose, protein, blood, ketones, nitrites, leukocyte esterase, albumin, creatinine (urine), urine albumin to creatinine ratio. Clinically significant laboratory abnormalities findings were based on investigator discretion.	From start of study intervention on Day 1 up to 28 days after last dose of study intervention (maximum up to 33 days)
Number of Participants With Clinically Significant Vital Signs	Vital signs included systolic and diastolic blood pressure, pulse rate/heart rate, temperature, respiratory rate, and oxygen saturation. Clinically significance vital signs findings were based on investigator discretion.	From start of study intervention on Day 1 up to 28 days after last dose of study intervention (maximum up to 33 days)

Secondary Outcome Measures

Outcome Measure	Time Frame
Plasma Concentrations Versus Time Summary of Sisunatovir	Day 3: Pre-dose, T1 and T2 hours post-dose; Day 5: Pre-dose; where T1 is the first analysis time point post-dose while T2 is the second analysis time point post-dose

Collaborators and Investigators

• Sponsor: Pfizer
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): February 15, 2024
• Primary Completion (Actual): September 3, 2024
• Study Completion (Actual): September 3, 2024

Study Registration Dates

• First Submitted: October 6, 2023
• First Submitted That Met QC Criteria: October 20, 2023
• First Posted (Actual): October 26, 2023

Study Record Updates

• Last Update Posted (Actual): December 30, 2025
• Last Update Submitted That Met QC Criteria: December 9, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: Lower Respiratory Tract Infection
• Additional Relevant MeSH Terms: Infections; RNA Virus Infections; Virus Diseases; Pneumovirus Infections; Paramyxoviridae Infections; Mononegavirales Infections; Respiratory Syncytial Virus Infections; Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Exercise; sisunatovir
• Other Study ID Numbers: C5241009; 2023-504425-39-00 (Registry Identifier: CTIS (EU))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No