AuthorisedTherapeutic exploratory (Phase II)Interventional

An open-label, single-arm extension study to evaluate the long-term safety, tolerability, and efficacy of KL1333 (napazimone) in patients with primary mitochondrial disease

This study is a follow-up to see how a medicine called KL1333 (also known as napazimone) works in adults who have a genetic condition called primary mitochondrial disease. It's an 'open-label' study, meaning everyone involved knows they are receiving the medicine. The main goals are to find out if the medicine is safe to take long-term, how well people tolerate it, and if it helps with their symptoms. Researchers will check for any side effects and see if conditions like metabolic decompensation (when the body's chemistry gets very unbalanced) or stroke-like episodes happen. They will also look at how patients feel, their tiredness levels, and their ability to do daily activities like standing up from a chair.

At a glance

Status

Authorised

Phase

Therapeutic exploratory (Phase II)

Sponsor

Pharming Technologies B.V.

Enrolment target

117

Start

21 May 2026

Adult patients with primary mitochondrial disease

What is this study about?

This study is designed to learn more about a medicine called KL1333, sometimes known as napazimone, for adults who have primary mitochondrial disease. This is a genetic condition that affects how the body's cells produce energy, leading to a wide range of symptoms. The researchers want to see how safe the medicine is when taken over a longer period, if people can take it without too many problems, and if it helps with their symptoms day-to-day. This particular study is a follow-up to earlier research, where the medicine showed some promise.

Because this is an 'open-label, single-arm' study, it means all participants will receive the medicine, and everyone involved (patients and researchers) will know that. There's no placebo group in this specific study. This design allows the researchers to gather more information about the medicine's long-term effects in a real-world setting, building on what they've learned before.

The main focus is on safety. The medical team will be carefully checking for any side effects, including serious ones like metabolic decompensation (when the body's chemical balance becomes dangerously off) or stroke-like episodes. They will also be looking at how the medicine affects everyday life, such as tiredness, how well people can move around, and their overall quality of life, using special questionnaires and physical tests. This helps them understand the bigger picture of how KL1333 might help people with primary mitochondrial disease.

Key takeaways

The study checks the long-term safety and effects of KL1333 for primary mitochondrial disease.
It's for adults with a confirmed diagnosis of primary mitochondrial disease.
All participants will receive the active medicine, KL1333.
Researchers will closely monitor for side effects and how symptoms change.
You'll have regular medical checks, blood tests, and fill out questionnaires.
Participation is voluntary, and you can withdraw at any time.

Who may be eligible?

This study is open to adults who have been diagnosed with primary mitochondrial disease. This means your doctors have identified that you have this specific condition, which affects how your body's cells create energy.

There isn't an upper age limit, so adults of any age are welcome to be considered. Both men and women can take part in this research.

The doctors running the study will carefully review your medical history and current health to make sure the study is a safe and suitable option for you. They will have specific criteria to decide if this particular treatment is right for you, based on your type of mitochondrial disease and overall health condition.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you an adult (18 years or older)?
Have you been diagnosed with primary mitochondrial disease?
Are you able to attend regular clinic visits?
Are you able to understand and follow study instructions?

Answer every question to see your result.

What does participation involve?

If you decide to join this study, you will be given the medicine KL1333. You'll have regular visits to the clinic where the study team will monitor your health very closely. These visits will involve various checks, such as physical examinations, recording your vital signs (like blood pressure and heart rate), and taking ECGs (heart tracings). You'll also have blood and urine tests to monitor your general health and see how the medicine is affecting your body.

A key part of your participation will be filling out questionnaires about your symptoms, how tired you feel, and how well you can perform daily activities. You might also do simple physical tests, like standing up from a chair several times. The study team will specifically watch out for any serious side effects, such as major changes in your body's chemistry or stroke-like events. The total duration of your participation, including how often your visits will be, will be explained to you by the study team.

Potential risks and benefits

Taking part in this study could potentially offer benefits, such as gaining access to a new medicine that might help manage your primary mitochondrial disease symptoms. You would also receive very close medical monitoring, which means your health would be regularly checked by specialists. However, like all medicines, KL1333 may have side effects, which could range from mild to serious. It's important to understand that your condition might not improve, or it could even get worse. You have the right to withdraw from the study at any time, for any reason, without it affecting your usual medical care.

Locations (7)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

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Unverified
Belgium
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Unverified
Germany
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Unverified
Czechia
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Unverified
Spain
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Unverified
Denmark
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Unverified
Italy
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Unverified
France

Common questions

What is primary mitochondrial disease?

It's a group of genetic conditions where the 'powerhouses' of your cells, called mitochondria, don't work properly, leading to a lack of energy and various symptoms.

What is KL1333 (napazimone)?

It's a new medicine being studied to see if it can help improve symptoms in people with primary mitochondrial disease.

Will I take KL1333 or a dummy pill (placebo)?

In this specific study, everyone who participates will receive the active medicine, KL1333. There is no dummy pill group.

What does 'open-label, single-arm' mean?

It means both you and the study team will know you are receiving the active medicine, and everyone in the study will get the same treatment, not a comparison to another drug or placebo.

What will happen during the study visits?

You'll have medical check-ups, blood and urine tests, heart recordings (ECGs), and answer questions about how you're feeling and your symptoms.