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A Randomized Study of Felzartamab versus Placebo to Assess Efficacy and Safety in Adults with Graves’ Disease

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What is this trial about?

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

The study focuses on adults with Graves’ Disease, an autoimmune condition that makes the thyroid gland produce too much hormone, leading to symptoms such as rapid heartbeat, weight loss, and anxiety. The treatment being tested is an intravenous medication called felzartamab, compared with a control solution of 0.9% Saline. The purpose of the study is to evaluate how well felzartamab works compared with placebo in improving thyroid function and safety in this population.

Participants receive a series of IV infusions of either the test medication or the control solution over several weeks, with regular clinic visits for blood tests and safety checks. Blood samples are used to measure levels of thyroid hormones, including free triiodothyronine (FT3) and free thyroxine (FT4), which indicate how active the thyroid is, and thyroid‑stimulating hormone (TSH), which helps regulate thyroid activity. The study also tracks whether participants become euthyroid—meaning their thyroid function returns to normal—without needing anti‑thyroid drugs, which are medicines that lower thyroid hormone production. Additional monitoring includes checking for side effects, serious side effects, and any immune reactions against the medication. The follow‑up period extends to 24 weeks to assess both short‑term and longer‑term outcomes.

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

    Consent and Baseline Screening

    After you join the study, you will provide written consent confirming that you understand the trial procedures.

    You will undergo baseline assessments that include a physical examination, medical history review, and blood tests to measure thyroid hormone levels and other safety parameters.

  2. Step 2

    Randomization to Treatment Group

    Based on the study design, you will be randomly assigned to receive either felzartamab or a placebo (0.9% saline).

    Random assignment ensures that the treatment you receive is determined by chance and not by personal factors.

  3. Step 3

    First Intravenous Infusion

    You will receive the assigned study medication as an intravenous (IV) infusion at the study center.

    The exact dose of felzartamab is defined by the trial protocol and is administered as a reconstituted lyophilized powder; the placebo is administered as a matching volume of 0.9% saline.

    The infusion is given over a period of time specified by the study staff.

  4. Step 4

    Immediate Post‑Infusion Observation

    Following the infusion, you will be observed for a short period to monitor vital signs and to detect any immediate reactions.

    Staff will check for symptoms such as fever, rash, or breathing difficulty and will record any findings.

  5. Step 5

    Ongoing Medication Management

    If you are taking anti‑thyroid drugs (ATD) for Graves’ disease, the study protocol may direct a reduction of the dose to 50 % or less of your baseline amount, based on your thyroid function test results.

    Your thyroid hormone levels (including FT3, FT4, and TSH) will be checked regularly to determine whether you can remain euthyroid (having normal thyroid function) without ATD.

  6. Step 6

    Week 12 Visit

    Approximately 12 weeks after the first infusion, you will return for a study visit.

    During this visit, blood samples will be taken to assess FT3, FT4, TSH, and ATD levels, and you will be evaluated for safety, including any adverse events.

  7. Step 7

    Week 24 Visit (Study End)

    At week 24, the final study visit will be conducted.

    The primary outcome – the proportion of participants who are euthyroid and no longer need ATD – will be measured.

    Additional assessments will include repeat thyroid hormone tests, monitoring for adverse events, and collection of blood to measure felzartamab concentration and any anti‑drug antibodies.

Who can join the trial?

5 criteria

  • You must have Graves’ disease that is currently active and test positive for thyroid‑stimulating hormone receptor antibodies (TRAb). These antibodies are proteins that can cause the thyroid to become overactive.
  • Your blood tests must show that free thyroxine (FT4) and free triiodothyronine (FT3) are within the normal range, that thyroid‑stimulating hormone (TSH) is low (suppressed), and that the level of TRAb is higher than the upper limit of normal (ULN). FT4 and FT3 are hormones made by the thyroid, and TSH is a hormone that tells the thyroid what to do.
  • You need to have been taking a stable dose of anti‑thyroid drugs (ATD) for at least 12 weeks before you are randomly assigned to a treatment group. Anti‑thyroid drugs are medicines that help control the overactivity of the thyroid.
  • You must agree not to donate blood or any blood products from the time you are screened for the study until the study ends. If you leave the study early, you must wait 90 days after the last dose of the study medication before donating blood.
  • You can be either male or female and must meet the age requirements set by the study, which include both children and adults.

Who cannot join the trial?

11 criteria

  • You cannot take part if you have had a thyroidectomy (surgical removal of the thyroid gland) or have been treated with radioactive iodine therapy.
  • You cannot take part if you have used an anti‑Neonatal Fragment Crystallizable Receptor (FcRn) therapy or intravenous immunoglobulin (IVIg) within the last 6 months before screening.
  • You cannot take part if you need to use high‑dose steroids on a regular basis.
  • You cannot take part if the dose of your antithyroid medication (ATD) was changed in the past 12 weeks, or if a change is expected before randomization (unless required for safety).
  • You cannot take part if you have active, moderate‑to‑severe, or sight‑threatening thyroid eye disease (TED), as measured by the clinical activity score (CAS), or if you need immediate treatment for TED such as systemic glucocorticoids, other biologic therapy, orbital radiation, or eye surgery.
  • You cannot take part if you have had any cancer (malignancy) within the past 5 years, except for certain skin cancers that were treated well (like in‑situ cervical cancer, basal or squamous cell skin cancer, or non‑melanoma skin cancer).
  • You cannot take part if you have had hyperthyroidism that is not caused by Graves’ disease, such as toxic multinodular goiter, an autonomous thyroid nodule, or acute inflammatory thyroiditis, or if you have ever had a thyroid storm.
  • You cannot take part if you have type 1 diabetes or type 2 diabetes with a hemoglobin A1c (HbA1c) level higher than 8% (a measure of blood sugar control).
  • You cannot take part if you are known or suspected to be allergic to felzartamab or any of its ingredients.
  • You cannot take part if you have used any immunosuppressive therapy within five drug half‑lives or 12 weeks before screening.
  • You cannot take part if you have another autoimmune disease that requires strong immune‑suppressing medicines such as cyclosporine, methotrexate, other biologics, or monoclonal antibodies.
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Investigated drugs

Felzartamab is an investigational drug being tested in this study. It is given by intravenous infusion and comes as a lyophilized powder that is mixed with a liquid before use. The purpose of the drug in the trial is to see if it can improve the symptoms and signs of Graves’ disease compared with a placebo. Researchers will watch how well it works and monitor any side effects to decide if it is safe and effective.

What is already known about the treatment

  • Felzartamab

    Felzartamab is given by intravenous infusion after reconstituting the lyophilized powder. It is an investigational drug currently in Phase 2 trials for Graves’ disease and is not yet approved for routine use. The medicine works by binding to the CD38 protein on immune cells, which reduces the production of harmful antibodies that drive the disease. It belongs to the class of monoclonal antibodies and is used as an immunosuppressive therapy.

  • 0.9% Saline

    0.9% Saline is administered intravenously as a sterile isotonic solution of sodium chloride. It is an established medical product that has been used for many decades as a fluid replacement and as a control in clinical trials. The solution simply provides water and salt to match the body’s natural balance, without any active drug effect. It is classified as an electrolyte solution or isotonic infusion.

Investigated diseases

Graves disease - Graves disease is an autoimmune condition that causes the thyroid gland to produce too much thyroid hormone. The immune system creates antibodies that mistakenly tell the thyroid to work faster. This results in a faster metabolism, which can cause weight loss, rapid heartbeat, heat intolerance, and nervousness. The thyroid often becomes enlarged, forming a goiter. In some people, the eyes may become bulging or uncomfortable. The activity of the disease can change over time, with periods of more or less hormone excess.
Trial detailsLast updated 17 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-526482-19-00Protocol code299GD201Estimated enrolment52 patientsSponsorBiogen Idec Research Limited

sourced from the EU Clinical Trials Register and site verification

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