A Study of S-337395 for Adults Not in Hospital with Respiratory Syncytial Virus Who Are at High Risk of Severe Disease

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What is this study about?

This clinical trial is studying Respiratory Syncytial Virus, which is a common virus that infects the breathing passages and lungs. The study will test a medication called S-337395, which is given as a film-coated tablet taken by mouth, and compare it to placebo. The medication S-337395 is a chemical compound that contains nitrogen-containing ring structures. The purpose of this study is to investigate how well S-337395 works against the virus in people who have an RSV infection.

The study will include adults who have symptoms of RSV but are not in the hospital and who are considered at high risk of their illness becoming more severe. Participants will be randomly assigned to receive either S-337395 or placebo. The study will look at whether the medication can reduce the amount of virus in the body and will measure this by taking samples from the nose and throat at different times during the study. These samples will be tested using a laboratory method to count how much virus is present.

During the study, doctors will check for any unwanted effects of the medication and will monitor participants through physical examinations, laboratory tests, heart tracings, and measurements of vital signs such as blood pressure and heart rate. The study will also track how RSV symptoms change over time, including breathing problems and general symptoms like fever or body aches, and will measure how long it takes for these symptoms to go away. Blood samples will be taken to measure the levels of S-337395 in the body at different times after taking the medication. The maximum daily dose of the medication will be 600 milligrams, and treatment will last for up to 6 days.

1 Enrollment and baseline assessment

Your participation begins after you have signed the informed consent form and your respiratory syncytial virus infection has been confirmed through a laboratory test. This virus is commonly known as RSV, which affects the respiratory system.

At this initial visit, a physical examination will be performed, your vital signs will be measured (such as blood pressure, heart rate, and temperature), and a 12-lead electrocardiogram will be recorded to check your heart’s electrical activity.

Blood samples will be collected for laboratory tests, and a nasopharyngeal swab will be taken (a sample from the back of your nose and throat) to measure the amount of virus in your system.

You will be asked to complete a questionnaire about your RSV symptoms, including respiratory symptoms (such as cough, shortness of breath, and nasal congestion) and systemic symptoms (such as fever, fatigue, and body aches). This establishes your baseline condition.

You will be randomly assigned to receive either S-337395 (the investigational medication in the form of a film-coated tablet taken by mouth) or a matching placebo (an inactive substance that looks identical to the medication).

2 First dose and early monitoring

You will take your first dose of the assigned medication (either S-337395 or placebo).

Blood samples will be collected at 12 hours and 24 hours after your first dose to measure the concentration of the medication in your bloodstream.

3 Visit 2 on day 2

You will return for an assessment on day 2 of the study.

A nasopharyngeal swab will be taken to measure the change in the amount of virus in your system compared to the baseline.

You will continue taking your assigned medication as instructed.

4 Visit 3 on day 4

You will return for an assessment on day 4 of the study.

Another nasopharyngeal swab will be taken to continue monitoring the viral load.

You will be asked about your symptoms and any side effects you may be experiencing.

You will continue taking your assigned medication as instructed.

5 Visit 4 on day 6

You will return for an assessment on day 6 of the study.

A nasopharyngeal swab will be taken to measure the viral load.

Your symptoms will be assessed using the same questionnaire to track changes in respiratory and systemic symptoms.

Blood samples will be collected to measure medication levels in your bloodstream.

This visit marks the completion of the primary assessment period for viral load changes.

6 Continued monitoring through day 6

Throughout the treatment period up to day 6, you will take your assigned medication daily as prescribed.

Blood samples will be collected at 12 hours and 24 hours after your last dose to measure the concentration of medication in your bloodstream.

Regular monitoring of your symptoms will continue to track when they improve or resolve, including each individual symptom and overall symptom burden.

Nasopharyngeal swabs will be collected at scheduled time points to measure changes in viral load and to determine when the virus becomes undetectable or reaches very low levels.

7 Safety monitoring throughout the study

Throughout your participation, any treatment-emergent adverse events (new medical problems or worsening of existing conditions that occur during the study) will be recorded and monitored.

Regular blood tests will be performed to monitor your laboratory values.

12-lead electrocardiograms will be recorded at scheduled visits to monitor your heart’s electrical activity.

Physical examinations and vital signs measurements will be performed at each visit to assess your overall health and safety.

Who Can Join the Study?

Age Requirements

You must be 18 years of age or older at the time of screening, or meet the minimum age for giving informed consent as required by local regulations if that age is higher than 18 years

Disease and Diagnosis Requirements

You must have been diagnosed with RSV infection, which stands for Respiratory Syncytial Virus infection, a virus that affects the breathing system
The diagnosis should preferably be confirmed using a rapid PCR test, which is a laboratory test that detects the virus’s genetic material, or another similar molecular-based test
If you had a positive RSV test result from another study or from a standard medical test within 72 hours before screening starts, and you meet all other requirements, this test result can be used to determine if you are eligible

General Health Requirements

Apart from the RSV infection, you must be medically stable based on your medical history, physical examination, vital signs (measurements like blood pressure, heart rate, and temperature), and a 12-lead ECG, which is a test that records the electrical activity of your heart
Any abnormalities found must be related to your underlying health condition or the RSV infection itself

Requirements for Men

Male participants must agree to follow specific rules during the study period and for at least 10 days after taking the last dose of the study medication
You must not donate semen during this time
You must either practice long-term abstinence from sexual intercourse as your usual lifestyle and agree to continue this, or you must use protection methods as follows:
Use a male condom when having sexual intercourse with a woman who could become pregnant and is not currently pregnant
Use a male condom during any activity where ejaculation could pass to another person

Informed Consent Requirements

You must be capable of giving signed informed consent, which means you understand what the study involves and agree to participate
You must understand the purpose of the study and the procedures that will be performed
You must be willing and able to follow the rules about what medications you can or cannot take during the study
You must be willing and able to follow all study procedures and attend all required assessments

Who Cannot Join the Study?

The source data does not provide specific exclusion criteria, which are reasons why a patient cannot participate in the study
Without detailed information about which conditions, medications, or situations would prevent participation, the specific reasons for exclusion cannot be listed
Generally, clinical trials may exclude patients based on factors such as other medical conditions, certain medications being taken, or specific test results, but these details are not available in the provided information

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country	Status
Alergo Med Osrodek Badan Klinicznych Sp. z o.o.	Tarnow	Poland

Other Sites

Site Name	City	Country
Medical Center Hera EOOD	Sofia	Bulgaria
Medical Center Pulmo-2018 EOOD	Haskovo	Bulgaria
Multiprofile Hospital For Active Treatment Dr. Tota Venkova AD	Gabrovo	Bulgaria
Pratia S.A.	Skorzewo	Poland
Medical Centre Nevromedics EOOD	Veliko Tirnovo	Bulgaria
Ogouwwstvynh Cbubgli Mlfvzgkn Ajom Oadvp Cyspwx Ksiylwcwb Cmqbwn srfn	Ostrowiec Swietokrzyski	Poland

Trial status

Country	Status	Recruitment Start
Bulgaria	Recruiting	01.12.2025
Poland	Not yet recruiting	01.12.2025

Trial locations

S-337395 is an investigational medication being studied for the treatment of respiratory syncytial virus (RSV) infection. This medication is designed to work against the virus in adults who have RSV symptoms but are not in the hospital, and who are at high risk of their condition becoming more severe. The study is testing whether this medication can help fight the virus and reduce its effects in the body.

Placebo is an inactive substance that looks like the real medication but contains no active treatment. It is used in this study to compare the effects of S-337395 against no treatment, helping researchers understand if the medication truly works.

Investigated diseases:

Respiratory syncytial virus infection

Respiratory Syncytial Virus Infection – Respiratory Syncytial Virus infection is a common viral illness that affects the breathing passages. The virus enters the body through the nose, mouth, or eyes and begins to multiply in the airways. It causes swelling and mucus production in the respiratory tract, making breathing difficult. The infection typically starts with symptoms similar to a common cold, including runny nose, cough, and sneezing. As the disease progresses, it can spread deeper into the lungs, affecting the smaller airways. Symptoms usually develop within four to six days after being exposed to the virus and may last for one to two weeks.

Trial ID:

2025-523156-31-00

Protocol code:

2402T1432

NCT ID:

NCT07214571

Trial Phase:

Therapeutic exploratory (Phase II)

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A Study of S-337395 for Adults Not in Hospital with Respiratory Syncytial Virus Who Are at High Risk of Severe Disease

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