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Long‑Term Safety and Tolerability of Frexalimab Drug Combination in Adults with Multiple Sclerosis

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What is this trial about?

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

A condition called multiple sclerosis affects the protective covering of nerves, leading to problems with movement, feeling, and vision. The trial investigates a new medicine called frexalimab, which is given either through a vein (intravenous) or under the skin (subcutaneous). Participants may also receive a standard oral drug, teriflunomide, and a background medication, colestyramine, which helps reduce certain side effects. Some participants receive a dummy treatment, known as placebo, to compare results. The main goal is to find out whether the new medicine is safe and can be tolerated over a long period.

During the study, participants will have regular visits where they take the assigned medication, undergo blood checks, and have brain scans using MRI to look for changes in lesions. The schedule includes multiple assessments spread over several years, allowing researchers to monitor any adverse events, track overall health, and observe how the disease progresses while on the treatment.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial Visit and Baseline Assessments

    You attend the first study visit after joining the trial. During this visit, the study team records your medical history, performs a physical examination, and conducts baseline laboratory tests and brain imaging (MRI) to document the condition of your multiple sclerosis.

    You also complete a safety questionnaire that includes the Columbia‑Suicide Severity Rating Scale (C‑SSRS) to assess any risk of suicidal thoughts.

  2. Step 2

    Start of Background Medication

    You begin taking colestyramine as a background treatment. The prescribed dose is 24 g taken orally each day, as directed by the study protocol.

  3. Step 3

    Start of Comparator Medication

    You start the comparator tablet, which contains teriflunomide. Each tablet provides a dose of 14 mg and is taken orally once daily, unless a matched placebo is assigned, in which case you take an identical‑appearing tablet without active drug.

  4. Step 4

    Administration of Test Medication

    You receive the test medication, frexalimab, by injection. The dose is 1800 mg and may be given intravenously (IV), subcutaneously (SC), or intramuscularly (IM) according to the study schedule. If a matched placebo is assigned, you receive an injection that looks the same but contains no active drug.

  5. Step 5

    Regular Follow‑Up Visits

    You attend scheduled follow‑up visits throughout the study. At each visit, the team checks for adverse events (AEs), performs laboratory tests, repeats the C‑SSRS questionnaire, and may repeat brain MRI scans to monitor disease activity.

    The frequency of these visits follows the study protocol and continues for the duration of the long‑term safety assessment.

  6. Step 6

    Study Completion and Final Assessment

    At the end of the study period, you undergo a final evaluation that includes a complete safety review, laboratory testing, and brain MRI. The results are used to determine the long‑term safety and tolerability of the study medications.

Who can join the trial?

3 criteria

  • Must have a diagnosis of relapsing‑remitting multiple sclerosis (RMS) or non‑relapsing secondary progressive multiple sclerosis (nrSPMS) and must have already taken part in certain earlier studies of the study drug, such as the Phase 2 ACT16877 study, any of the four Phase 3 frexalimab studies (EFC17919A, EFC17919B, EFC17504, EFC18098), or be planned for the Phase 2 biomarker study ASY22814. IMP means the investigational medicinal product, the drug being tested.
  • Must use birth control methods (contraception) that follow the rules in your country or region, whether you are male or female, because the study requires it.
  • Must be able to understand what the study involves and sign a written informed consent form, showing you agree to take part.

Who cannot join the trial?

10 criteria

  • If the study drug (called the investigational medicinal product (IMP)) must be stopped according to the study rules, you cannot take part.
  • If you are living in a prison, a detention center, or are otherwise legally required to stay in an institution, you are not eligible.
  • If you have a long‑lasting or repeatedly active infection (including a fever of 38 °C or higher) or a special type of infection that takes advantage of a weak immune system (called an opportunistic infection, for example progressive multifocal leukoencephalopathy PML), you cannot join.
  • If your blood tests show very low levels of certain antibodies (IgG that is at least 20 % below the normal lower limit, or IgM that is at least 10 % below the normal lower limit), you are excluded.
  • If you have a serious heart, liver, hormone, brain‑related, or other major disease that would make the study difficult or put you at risk, you cannot participate.
  • If you have evidence, suspicion, or a high risk of blood‑clot problems (thromboembolic events), a heart attack (myocardial infarction), a stroke, or a clotting disorder called antiphospholipid syndrome, or if you need medicines that prevent clots (antithrombotic treatment), you are not allowed.
  • If the doctor believes you are no longer getting a therapeutic benefit from the study treatment, you will be excluded.
  • If you show a risk of suicide on the C‑SSRS questionnaire (answer “yes” to specific questions about suicidal thoughts or actions), you cannot take part.
  • If you need to keep using a medication that the study specifically forbids, you are not eligible.
  • If the laws or regulations of your country prevent you from joining the trial, you cannot participate.
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Investigated drugs

  • Teriflunomide (AUBAGIO)

    is an oral medication that is already approved for treating multiple sclerosis. In this study it is used as a comparator, meaning participants taking it are compared with those receiving the new drug to see how the new treatment measures up in safety and tolerability.

  • Colestyramine

    is a powder taken by mouth that works by binding certain substances in the gut. In this trial it is given to all participants as background therapy to help control cholesterol and possibly reduce side effects from other medicines.

  • Frexalimab

    is an experimental antibody that is given by injection (intravenous, subcutaneous, or intramuscular). It is the test product being studied to see if it can be safely used over a long period in people with multiple sclerosis. The trial is looking at how well participants tolerate this new therapy and whether any safety concerns arise.

What is already known about the treatment

  • Aubagio

    It is taken as a 14 mg film‑coated tablet that is swallowed with water. The drug is approved and widely used for treating relapsing forms of multiple sclerosis. It works by blocking an enzyme needed for the growth of certain immune cells, which helps lower inflammation. It is classified as a disease‑modifying therapy, specifically a pyrimidine synthesis inhibitor.

  • Colestyramine

    This medication comes as a powder that is mixed with water or another liquid to make a thick drink taken by mouth. It is an established, approved drug used to lower cholesterol and to bind bile acids in the gut. It attaches to bile acids, preventing their re‑absorption and thereby reducing cholesterol levels. It belongs to the class of bile‑acid sequestrants.

  • Frexalimab

    It is supplied as a clear solution for injection and is given either intravenously or subcutaneously at a dose of 1800 mg. The product is currently in phase‑3 clinical trials and is not yet approved for general medical use. It works by binding to a specific protein on immune cells, blocking their activation and reducing the immune attack on nerve fibers. It is classified as a monoclonal antibody that targets immune pathways.

Investigated diseases

Multiple sclerosis - Multiple sclerosis is a chronic condition in which the immune system mistakenly attacks the protective covering of nerve fibers in the brain and spinal cord. This damage disrupts the flow of electrical signals, leading to symptoms such as weakness, numbness, vision problems, and balance difficulties. Over time, new areas of damage can appear, causing additional symptoms to develop. The disease often follows a pattern of episodes of new or worsening symptoms followed by periods of stability, but many people later experience a gradual increase in disability even without clear relapses. Magnetic resonance imaging can show the formation of new lesions that reflect ongoing disease activity.
Trial detailsLast updated 2 Nov 2026
Age18+ yearsPhasePhase IIITrial ID2026-525688-41-00Protocol codeLTS18002Estimated enrolment1 747 patientsSponsorSanofi-Aventis Recherche & Developpement

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