AuthorisedTherapeutic use (Phase IV)Interventional

Reduced-dose versus full-dose systemic thrombolysis for high-risk pulmonary embolism: a multicentre, randomised, open-label, blinded-endpoint trial

A pulmonary embolism is a serious, life-threatening blood clot that blocks blood flow in the lungs. In severe cases, emergency doctors use a powerful clot-busting drug called alteplase to rapidly break down the blockage and take strain off the heart. While the standard full dose of alteplase is very effective, it carries a known risk of major internal bleeding, including bleeding in the brain. This clinical trial is testing whether a lower, reduced dose can work just as effectively as the full dose to stabilise patients and save lives, but with fewer dangerous bleeding side effects. The study involves adults admitted to hospital with severe lung clots. Patients receive either the reduced dose or the standard dose through a drip. Doctors monitor them closely during the first week and check their recovery after 30 days to see which approach offers the best balance of safety and effectiveness.

At a glance

Status

Authorised

Phase

Therapeutic use (Phase IV)

Sponsor

Vaestra Goetalandsregionen, University Of Gothenburg

Enrolment target

280

Start

02 Sep 2026

Pulmonary embolism

What is this study about?

A pulmonary embolism happens when a blood clot travels to the lungs and blocks a major artery. In high-risk cases, this blockage suddenly stops normal blood flow, causing dangerously low blood pressure, severe breathlessness, and strain on the heart. This is a critical medical emergency that requires fast hospital treatment to restore blood flow before permanent damage occurs.

The standard emergency treatment is a medicine called alteplase, given through a vein. Alteplase acts quickly to dissolve the blockage, allowing blood to circulate normally again. However, because it dissolves clots throughout the entire body, it also carries a significant risk of causing serious bleeding elsewhere, such as in the stomach or the brain. Finding a treatment that breaks down the clot while keeping bleeding risks as low as possible is a major goal in emergency medicine.

This trial investigates whether giving a reduced dose of alteplase works just as well as the standard full dose. Doctors are comparing the two doses directly to see if the lower amount can stabilise blood pressure, restore healthy oxygen levels, and protect patients just as reliably as the standard amount.

If the lower dose proves to be just as effective, it could change emergency care guidelines across the NHS and worldwide. A lower dose could provide patients with the life-saving benefits of clot-busting therapy while substantially reducing the danger of harmful bleeding complications.

Key takeaways

Tests whether a lower dose of the clot-busting drug alteplase works as well as the full dose for severe lung blood clots.
Aims to find out if the lower dose reduces the risk of serious bleeding complications.
Open to adults aged 18 and older receiving emergency hospital care for a high-risk pulmonary embolism.
Involves close hospital monitoring over the first 7 days, with a final check at 30 days.
Participation is entirely voluntary and does not change your right to standard emergency NHS care.

Who may be eligible?

This study is for adults aged 18 and over who have been admitted to hospital with a sudden, severe (high-risk) pulmonary embolism. "High-risk" means the clot is severely affecting your heart and causing dangerously low blood pressure or severe oxygen problems that require urgent clot-dissolving treatment.

Because this is an emergency study, the hospital medical team identifies eligible patients immediately upon diagnosis. Both men and women can take part.

You may not be eligible if you have conditions that make clot-busting drugs too dangerous. This includes recent major surgery, a recent stroke, active internal bleeding, or severe head injuries. The medical team will carefully evaluate your health history before deciding if the study is safe for you.

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.

You are aged 18 or older.
You have been diagnosed in hospital with a sudden, severe blood clot in the lungs (pulmonary embolism).
Your blood pressure or oxygen levels are critically affected by the clot.
You need immediate, emergency clot-dissolving medication.
You do not have a condition that makes clot-busting drugs unsafe, such as recent major bleeding or head injury.

Answer every question to see your result.

What does participation involve?

Participation takes place while you are in hospital receiving emergency treatment. You will be randomly assigned by a computer to receive either the lower dose or the standard full dose of alteplase through an intravenous drip into a vein. You will be cared for in an intensive care or high-dependency unit, where doctors and nurses will closely monitor your heart rate, blood pressure, oxygen levels, and blood tests over the first 24 to 48 hours. Your progress will be tracked throughout your hospital stay, especially during the first 7 days. A final follow-up check will take place around 30 days after treatment to see how well you have recovered.

Potential risks and benefits

A potential benefit of joining is receiving a lower dose of medicine that might clear the clot just as well while reducing your risk of dangerous bleeding. However, there is a possibility that a lower dose might not break down the clot as quickly, or that either dose could cause bleeding complications ranging from minor bruising to serious internal bleeding. Your safety is monitored continuously, and rescue treatments are always available. Taking part is completely voluntary; you or your family can withdraw at any time without your regular NHS medical care being affected in any way.

Locations (3)

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

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Unverified
Denmark
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Unverified
Sweden
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Unverified
Norway

Common questions

What is alteplase?

Alteplase is an emergency clot-busting medicine given through a drip to quickly dissolve life-threatening blood clots.

Can I choose which dose I receive?

No. A computer randomly decides whether you receive the lower dose or standard dose, ensuring the study results are completely fair.

What happens if the lower dose does not work?

You will be watched constantly in an intensive care setting. If your condition does not improve or gets worse, doctors will immediately step in with standard rescue treatments.

How long will I be in the study?

The medicine is given right away, intensive monitoring lasts for the first week in hospital, and a final recovery check happens at 30 days.

Does taking part cost anything?

No. The trial is part of hospital care, and all trial medications and assessments are provided free of charge.