Long‑Term Safety and Tolerability Study of Oral KT‑621 in Adults with Uncontrolled Moderate‑to‑Severe Eosinophilic Asthma

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What is this study about?

The study focuses on Uncontrolled Moderate to Severe Eosinophilic Asthma, a type of asthma in which breathing is frequently difficult and a specific white blood cell called an eosinophil is often elevated, causing inflammation in the airways. Participants will receive an oral tablet containing KT-621, which is taken by mouth once daily. The medication is being tested to see how it works over an extended period in people whose asthma has not been well controlled with existing treatments.

The main goal is to evaluate the long‑term safety and tolerability of the drug. After enrollment, participants will continue taking the tablet for up to one year, returning for regular check‑ins where doctors will look for any side effects and will assess lung function using a test called FEV1, which measures how much air can be exhaled forcefully in one second. Symptom control will be measured with a short questionnaire known as the ACQ-5, and overall quality of life related to asthma will be evaluated with the AQLQ(S) questionnaire. These visits help ensure participants are monitored closely while remaining on the study medication.

1 baseline visit and assessments

you attend the first study visit after joining the trial. this visit is called the baseline visit.

the study team will perform tests to measure your lung function, such as pre‑bronchodilator FEV1 (the amount of air you can force out of your lungs in one second before using a medication that opens the airways) and post‑bronchodilator FEV1 (the same measurement after using that medication).

you will also complete questionnaires about your asthma symptoms (ACQ‑5) and your asthma‑related quality of life (AQLQ(S)).

2 start study medication

after the baseline assessments, you will begin taking the study drug kt‑621.

kt‑621 is an oral tablet taken by mouth.

the dose specified in the study is 0 mg per tablet; you will follow the dosing schedule provided by the study team and continue the medication for up to week 52 (one year).

3 regular safety monitoring

throughout the 52‑week period you will be asked to report any new health problems or side effects. these are called treatment‑emergent adverse events (TEAEs) and are recorded from the baseline visit until week 52.

if a serious health problem occurs, it will be recorded as a treatment‑emergent serious adverse event (SAE).

the study team may schedule additional visits or phone contacts to check your safety, but the exact timing is not specified beyond the baseline and week‑52 visits.

4 final visit at week 52

at the end of the 52‑week period you will return for a final study visit.

the same lung function tests (pre‑ and post‑bronchodilator FEV1) and questionnaires (ACQ‑5 and AQLQ(S)) that were done at baseline will be repeated to see how they have changed.

blood samples will be taken to measure the concentration of kt‑621 in your plasma.

the study will also summarize any adverse events that occurred during the year.

Who Can Join the Study?

Must have uncontrolled moderate to severe eosinophilic asthma – a type of asthma that is not well‑controlled with usual medicines and involves high levels of a white‑blood cell called eosinophils.
Must have finished all visits of the earlier parent study up to its end‑of‑treatment visit.
Must be willing and able to attend scheduled visits, follow the treatment plan, give laboratory samples, complete study procedures, and fill out an electronic diary (e‑diary) for the whole study.
Must agree to use birth control as required by the study and local regulations (contraceptive requirements).
Both males and females are allowed to participate.
Participants of any age that the study permits (including children and adults) may be eligible.

Who Cannot Join the Study?

You cannot join if you had a clinically significant change in health status during the earlier study, meaning a health change that doctors consider important enough to affect safety, study measurements, or your ability to follow study steps.
You cannot join if you experienced an adverse event (AE) in the earlier study that doctors felt could make continued treatment unsafe for you.
You cannot join if you were permanently taken off the earlier study for any reason, known as meeting permanent discontinuation criteria or having the study treatment stopped.
You cannot join if you are a member of the company running the study (Sponsor) or the study site’s research team, or if you are an immediate family member of anyone on that team.
You cannot join if the doctor believes you are unsuitable for any other reason, such as a likely risk of not following the study procedures (noncompliance).

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country	Status
Policlinico “Tor Vergata”, Università degli Studi di Roma TOR VERGATA	Rome	Italy
Hospital Jerez de la Frontera	Jerez De La Frontera	Spain

Other Sites

Site Name	City	Country
Azienda Universitaria Ospedaliera Consorziale Policlinico Bari	Bari	Italy
Lungenpraxis Hohenzollerndamm	Berlin	Germany
Hospital Universitario De Canarias	La Laguna	Spain
Clinica Respira-Dr.Juanola	Mataró	Spain
Pecjgana abealvkwdx Hpxveuuu sjvbwv	Spisska Nova Ves	Slovakia
Aasxpa sgrlcp	Kosice	Slovakia
Ipufv Ofurifbo Ppmtsacidkf See Mpqsysk	Genoa	Italy
Ahyabut Oqfftjimedg Ugmeyzkhwfmtx Fkbqvfys Im Dl Nlqybk	Naples	Italy
Avjzrsl Sfyabhwigyxivz Tmmxwylogohk Sufgn Plzyh E Cuqxd	Milan	Italy
Byjzkptzbfjvvrqmkewpumrpcyjk Blm Pjgd Dqf Mim Gfrcdju Hdsirryb Dco Mnz Ahhbpee Bmswxx Gna	Leipzig	Germany
Aosxpst Oxntqjhomezgrhmpywakrxetr Sohe Aizcj	Rome	Italy
Ayelg szvhhy	Bardejov	Slovakia
Pwdk Sjqjyyw Gyws	Leipzig	Germany
Hwikxlcn Ujwdnneeujxzy 1d Dk Otnjscm	Madrid	Spain
Hfpcyvzs Uoyotwgcwjinn Msetujp Dg Vdyyutzcnl	Santander	Spain
Htvmxpvs Uhhfsvufaavqh Povlqk Dzx Myx	Cadiz	Spain
Hejvccjz Ujkqbetuimkyl Ioyiuqm Ldtpug	Madrid	Spain

Trial status

Country	Status	Recruitment Start
Germany	Not yet recruiting	01.09.2026
Italy	Not yet recruiting	01.09.2026
Slovakia	Not yet recruiting	01.09.2026
Spain	Not yet recruiting	01.09.2026

Trial locations

KT-621 is an experimental oral tablet being studied to see if it is safe and well‑tolerated when taken for a long time by people with asthma. In this trial, participants who have already taken KT-621 in an earlier study continue to receive the same medication, and researchers closely monitor them for any side effects or health concerns over an extended period. The goal is to learn whether the drug can be used safely in the long term for managing asthma.

Uncontrolled moderate-to-severe eosinophilic asthma – This is a type of asthma characterized by high levels of eosinophils, a type of white blood cell, in the airways. It causes frequent wheezing, shortness of breath, and coughing that are not well controlled with standard inhaled therapies. Symptoms tend to worsen over time, leading to more frequent flare‑ups and increased need for rescue medication. The inflammation can cause the airways to become increasingly narrow and less responsive to treatment. As the disease progresses, patients may experience greater limitation in daily activities due to persistent breathing difficulty.

Trial ID:

2026-526241-98-00

Protocol code:

KT621-AS-203

Trial Phase:

Therapeutic exploratory (Phase II)

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Long‑Term Safety and Tolerability Study of Oral KT‑621 in Adults with Uncontrolled Moderate‑to‑Severe Eosinophilic Asthma

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?