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Stopping warfarin sodium, fluindione, or acenocoumarol in low‑risk thrombotic antiphospholipid syndrome patients after antibody loss

Verified siteRegistered drugNo placebo
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What is this trial about?

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

The trial focuses on people with thrombotic antiphospholipid syndrome, a condition in which the immune system makes proteins that raise the chance of blood clots. Participants are taking an anticoagulant – a medicine that helps keep blood from clotting – such as warfarin, fluindione or acenocoumarol. The purpose of the study is to find out whether stopping the anticoagulant after the harmful antibodies disappear is as safe as continuing the medication in terms of preventing new clots.

In the study, participants are randomly assigned to either stop the anticoagulant or keep taking it, and they are followed for a period of time with regular check‑ups. During these visits, doctors look for any new clot events, record any serious bleeding (for example, bleeding inside the brain or a drop in blood‑cell count that needs a transfusion), and ask about overall health and quality of life using a questionnaire. The study also tracks whether the antibodies come back and notes other factors that might affect clot risk, such as age, surgery or infection. All information is collected to compare the two groups and determine the safest approach.

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

    Baseline Assessment

    You will attend an initial visit where the study team records your medical history and performs blood tests to measure antiphospholipid antibodies (aPL).

    If you are assigned to continue anticoagulation, you will receive a prescription for an oral tablet such as warfarin (Coumadine 2 mg), fluindione (Prevican 20 mg), or acenocoumarol (Sintrom 4 mg).

  2. Step 2

    Medication Administration

    You will take the prescribed tablet by mouth once each day.

    The exact dosage is determined by your physician and may be adjusted during the trial based on blood test results.

  3. Step 3

    Routine Monitoring Visits

    You will return to the clinic at regular intervals for blood tests that check both your clotting status and the presence of aPL.

    During these visits the study doctor may modify the dose of the anticoagulant to keep your blood clotting within the target range.

  4. Step 4

    Antibody Loss Assessment

    If the laboratory results show that antiphospholipid antibodies are no longer detectable, the study team will inform you of this finding.

    The loss of aPL is the key criterion used to consider stopping the anticoagulant.

  5. Step 5

    Anticoagulant Cessation

    If you and your physician agree, you will discontinue the oral anticoagulant.

    You will continue to attend follow‑up visits to monitor for any signs of new clotting or bleeding events.

  6. Step 6

    Ongoing Follow‑Up

    You will keep attending scheduled visits for the remainder of the study period.

    These visits include assessments of health status, recording of any recurrent thrombosis, major bleeding, or other adverse events, and completion of quality‑of‑life questionnaires.

  7. Step 7

    Final Study Visit

    At the end of the trial you will undergo a final evaluation that summarizes your overall health outcomes and completes the last study questionnaires.

Who can join the trial?

5 criteria

  • You must be an adult aged 18 years or older.
  • You must sign a written consent form agreeing to join the study.
  • You must have a diagnosis of primary or secondary thrombotic antiphospholipid syndrome (APS) that meets the 2023 ACR/EULAR classification criteria. (Primary means APS alone; secondary means APS together with another autoimmune disease.)
  • You must show loss of antiphospholipid antibodies (aPL), specifically lupus anticoagulant (LA), anticardiolipin (aCL), and anti‑beta‑2‑glycoprotein I (aβ2GPI) antibodies. This means the test results are below the 99th percentile (normal range) on at least two separate measurements taken at least 12 months apart, and one of those tests was done within the three months before joining the study.
  • You must have been taking a vitamin K antagonist (VKA) blood thinner (such as warfarin) for more than 12 months.

Who cannot join the trial?

14 criteria

  • History of severe venous thrombosis – having had serious blood clots in the veins, such as a large lung clot (massive pulmonary embolism), long‑term lung pressure problems (chronic thromboembolic pulmonary hypertension), or clots in the liver, intestines, kidneys, or brain.
  • Mechanical heart valve or any condition that needs anticoagulation with a VKA – an artificial heart valve or another disease that requires a blood‑thinning medicine called a vitamin K antagonist (VKA).
  • Pregnancy or breastfeeding – being pregnant or feeding a baby.
  • Deprived of freedom or under a legal protective measure – not able to make personal decisions because of imprisonment, guardianship, or similar legal restrictions.
  • No health‑insurance coverage – not belonging to any health‑insurance system.
  • Participating in another interventional study – already enrolled in a different clinical trial that involves a medication, device, or other experimental treatment.
  • History of arterial thrombosis – having had blood clots in arteries, which are the vessels that carry blood away from the heart.
  • Repeated venous clots while taking VKAs – having multiple vein clots even though you were already using a VKA blood thinner.
  • History of catastrophic antiphospholipid syndrome (CAPS) – a rare, severe condition where many small clots form suddenly throughout the body.
  • Triple aPL positivity – testing positive for three different antiphospholipid antibodies, which are proteins that can increase clot risk.
  • Allergy to the study medication or its ingredients – known hypersensitivity (allergic reaction) to the active drug or any of its added substances.
  • Malignant hypertension – extremely high blood pressure that can damage organs.
  • Severe liver disease – serious impairment of liver function.
  • Active cancer – currently having a malignant tumor (cancer).
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Investigated drugs

  • Warfarin

    is a tablet taken by mouth that helps prevent blood clots. It works by reducing the body’s ability to use vitamin K, which is needed for clotting. In this study, participants who continue taking warfarin keep their usual blood‑thinning protection, while the trial also looks at what happens if they stop taking it after certain antibodies disappear.

  • Fluindione

    is another oral blood‑thinner that belongs to the same group of medicines as warfarin. It also blocks the action of vitamin K, making it harder for blood to form clots. In the trial, fluindione is used as one of the options for ongoing anticoagulation, and the researchers are testing whether patients can safely stop it when their antibody levels fall.

  • Acenocoumarol

    is a third tablet‑type anticoagulant that works by the same vitamin K‑blocking method. It is taken to keep blood from clotting too easily. The study includes acenocoumarol as a standard treatment that participants may be using, and it examines if stopping this medication after antibody loss is as safe as continuing it.

What is already known about the treatment

  • COUMADINE 2 mg, comprimé sécable

    This medication is taken by mouth as a small tablet that can be split. It is a well‑known and widely approved drug that has been studied for many years. It is mainly used to prevent blood clots in conditions such as atrial fibrillation, deep‑vein thrombosis, and after certain surgeries. It works by blocking the recycling of vitamin K, which stops the liver from making several clotting proteins, and it belongs to the vitamin K antagonist class of anticoagulants.

  • PREVISCAN 20 mg, comprimé quadrisécable

    This drug is also an oral tablet that can be divided into four parts for dosing. It is approved in several countries but is less commonly used than warfarin, so the amount of research is smaller. It is prescribed to treat or prevent dangerous blood clots, especially in patients who need long‑term anticoagulation. Like other vitamin K antagonists, it blocks the enzyme that recycles vitamin K, reducing the production of clotting factors, and it is classified as a vitamin K antagonist.

  • Sintrom 4 mg, comprimés

    Sintrom is taken orally as a tablet that can be split for dose adjustment. It is an established anticoagulant that is approved and widely used throughout Europe. The drug is used to stop new clots from forming and to keep existing clots from growing in conditions such as atrial fibrillation and venous thromboembolism. Its action is the same as other vitamin K antagonists: it interferes with vitamin K recycling, lowering the levels of clotting proteins, and it belongs to the vitamin K antagonist group.

Investigated diseases

Thrombotic antiphospholipid syndrome - This is an autoimmune condition in which the body produces antiphospholipid antibodies that make blood more likely to clot. People with the disease develop clots in veins or arteries, which can appear in various parts of the body. The condition often follows a pattern of occasional clotting episodes that may recur over time. When the antibodies disappear from the blood, the tendency to clot may lessen, but the underlying risk can still remain. Ongoing monitoring is needed because new clot events can still occur as the disease progresses.
Trial detailsLast updated 14 Nov 2026
Age18+ yearsPhasePhase IIITrial ID2026-526448-12-00Protocol codeAPHP251593Estimated enrolment234 patientsSponsorAssistance Publique Hopitaux De Paris

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