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Reduced-dose versus full-dose alteplase for high-risk acute pulmonary embolism patients: a randomized multicenter trial

Fast replyRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

A serious condition called Pulmonary embolism occurs when a blood clot blocks one of the arteries in the lungs, causing sudden shortness of breath and low blood pressure. The study looks at patients who have a high‑risk form of this condition, meaning they are very ill and need urgent treatment. The medication being tested is a clot‑dissolving drug called alteplase, which is given through an IV line (a thin tube placed in a vein) to help break up the clot.

The goal of the research is to find out whether a lower dose of the drug works just as well as the standard full dose for these patients. Participants are randomly assigned to receive either the reduced dose or the full dose, and they are monitored closely for about a week to see how they respond, including any need for life‑support measures or repeat clot events.

During the study, doctors watch for signs of improvement such as stable blood pressure, better oxygen levels, and the ability to breathe without extra machines. They also keep track of any serious bleeding problems. The overall plan is to compare the two dosing strategies to see if the lower amount can provide the same benefit with potentially fewer side effects.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomisation to treatment group

    After you agree to take part, you are randomly assigned to receive either a reduced dose or a full dose of alteplase. the assignment is done by a computer and you do not choose the group.

  2. Step 2

    Administration of alteplase

    The study drug is given once by iv infusion. if you are in the full‑dose group, you receive 100 mg of alteplase. if you are in the reduced‑dose group, you receive a lower amount as defined by the study protocol. the infusion is delivered over a short period of time under medical supervision.

  3. Step 3

    Immediate monitoring during infusion

    While the infusion is running, staff continuously check your blood pressure, heart rate, breathing, and oxygen level. they also watch for any signs of bleeding or other adverse reactions.

  4. Step 4

    Assessment of clinical improvement at 6 hours

    Six hours after the infusion ends, doctors evaluate whether your condition has improved. improvement is defined as a better shock stage or a lower amount of oxygen needed to keep your blood oxygen saturation at 94% or higher.

  5. Step 5

    Assessment of clinical deterioration within 24 hours

    Within the first 24 hours, the team looks for any worsening of your heart or lung function that would require emergency measures such as CPR, intubation, or use of a device called va‑ecmo. if such events occur, they are recorded as clinical deterioration.

  6. Step 6

    Hospital monitoring through day 7

    You remain in the hospital for up to seven days. during this time staff monitor for several outcomes, including death from any cause, need for CPR or va‑ecmo, a new pulmonary embolism, major bleeding, and any additional rescue treatments such as extra alteplase or surgical procedures.

  7. Step 7

    Follow‑up assessment at 30 days

    About thirty days after the start of treatment, you have a follow‑up visit (or a phone call) to check your overall health. the visit includes checking whether you have survived, whether any bleeding events have occurred, and whether any further treatment was needed since leaving the hospital.

Who can join the trial?

5 criteria

  • Be an adult (age 18 years or older).
  • Have a recent pulmonary embolism (a blood clot in the lungs) confirmed by a special CT scan called CTPA or by a traditional pulmonary angiography. If you are too unstable for imaging, doctors may use a bedside heart ultrasound (echocardiography) that shows pressure overload of the right side of the heart, after they have ruled out other causes such as irregular heartbeat or severe infection.
  • Be considered at high risk of early death, meaning you meet at least one of these conditions: cardiac arrest (heart stopped and then restarted), obstructive shock (very low blood pressure below 90 mm Hg or need for medicines to keep it up, plus signs that organs are not getting enough blood such as high lactate level, confused thinking, or cold, clammy skin), or persistent low blood pressure (below 90 mm Hg or a drop of 40 mm Hg for more than 15 minutes that is not caused by a new heart rhythm problem, low blood volume, or infection).
  • Also be high risk because of heart and breathing problems: the right side of the heart must look enlarged or not working well on an ultrasound or CT scan (right‑ventricle to left‑ventricle size ratio greater than 1), you must have higher than normal levels of a heart protein called troponin, and you must need strong breathing support (such as a face mask delivering at least 12 L of oxygen per minute, or high‑flow nasal oxygen, or a non‑invasive ventilator with at least 60% oxygen) to keep your blood oxygen level at 94% or higher.
  • If you are a female who could become pregnant, you must have a negative urine or blood pregnancy test.

Who cannot join the trial?

13 criteria

  • Having an ongoing heart stoppage (cardiac arrest) or needing emergency machines that take over heart and lung function (extracorporeal cardiopulmonary resuscitation or VA‑ECMO) at the time of enrollment, which is called a catastrophic pulmonary embolism.
  • Being known to be allergic (hypersensitivity) to the study drug (alteplase) or any of its inactive ingredients (excipients).
  • Having any condition that makes clot‑busting treatment unsafe, such as:
    • A previous brain bleed (hemorrhagic stroke).
    • A brain clot (ischemic stroke) that occurred in the last 6 months.
    • A brain tumor (central nervous system neoplasm).
    • A serious injury, major surgery, or serious head injury in the past 3 weeks.
    • Ongoing serious bleeding (active bleeding) or a known tendency to bleed heavily (severe bleeding diathesis).
    • Regular use of full‑dose blood‑thinning medication (full‑dose anticoagulation) before arriving at the hospital.
    • Having already received clot‑busting therapy, surgical removal of the clot, or a catheter‑directed procedure for the current pulmonary embolism before being assigned to the study.
    • Currently taking part in another research study that could interfere with this trial.
    • Having any other health problem that the treating doctor believes would make participation too risky.
    • Not having health‑insurance or social‑security coverage when required by local regulations.
    • Being pregnant.
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Investigated drugs

Alteplase is a medication that helps dissolve blood clots. In this study it is given through an IV (intravenous) infusion to treat patients with a serious lung blood‑clot condition called high‑risk pulmonary embolism. The trial compares a lower amount of the drug (reduced dose) with the usual higher amount (full dose) to see if the smaller dose works just as well at preventing death, the need for emergency heart‑lung support, or another clot forming soon after treatment.

What is already known about the treatment

  • Alteplase

    Alteplase is administered by IV infusion, typically 100 mg given slowly through a vein. It is an approved clot‑dissolving drug that is widely used for acute pulmonary embolism, heart attacks and certain strokes. The medicine works by converting plasminogen into plasmin, an enzyme that breaks down the fibrin mesh of blood clots. It is classified as a tissue‑type plasminogen activator, a type of thrombolytic medication.

  • Actilyse

    Actilyse is supplied as a sterile solution for injection/infusion and is given by IV infusion, usually 100 mg over a short period. It is a branded form of alteplase that is approved for treating high‑risk pulmonary embolism and other serious clot‑related emergencies. Like alteplase, it activates plasminogen to form plasmin, which then dissolves the fibrin strands that hold clots together. It belongs to the thrombolytic drug class, specifically tissue‑type plasminogen activators.

Investigated diseases

Pulmonary embolism - A pulmonary embolism occurs when a blood clot travels to and blocks an artery in the lungs. The blockage reduces blood flow to part of the lung, causing sudden shortness of breath, chest discomfort, and rapid breathing. As the clot remains, pressure in the lung vessels can rise and the heart may have to work harder, which can lead to worsening symptoms if the clot does not dissolve or shrink.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-515904-37-00Protocol codeREDSTEMEstimated enrolment280 patientsSponsorUniversity Of Gothenburg

sourced from the EU Clinical Trials Register and site verification

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