Upon joining the study, you will be randomly assigned to receive either mezagitamab or placebo. The placebo is an inactive substance that looks like the actual medication but contains no active ingredient.

The medication will be administered as a subcutaneous injection, which means it will be injected under the skin.

This is a double-blind study, meaning neither you nor the medical staff will know whether you are receiving mezagitamab or placebo during the treatment period.

Before starting the treatment, your baseline platelet count will be measured. Platelets are small blood cells that help your blood to clot.

Your symptoms will be assessed using a questionnaire called the ITP-PAQ, which evaluates how immune thrombocytopenia affects your daily life.

Any bleeding events will be documented using the ITP-BAT assessment tool, which measures bleeding in different areas of your body including skin, mucous membranes, and internal organs.

Your platelet count will be measured weekly throughout the 24-week treatment period.

The medical team will monitor whether your platelet count reaches at least 50,000 per microliter, which is considered a therapeutic target.

Special attention will be given to platelet measurements taken between week 19 and week 24, as these will determine if you have achieved a durable response to treatment.

At week 16, your platelet count will be measured before receiving the scheduled injection.

You will complete the ITP-PAQ questionnaire again to assess any changes in your symptoms compared to the beginning of the study.

The medical team will evaluate whether your platelet count has reached at least 50,000 per microliter at this time point.

At week 24, which marks the end of the main treatment period, comprehensive assessments will be performed.

Your platelet count will be measured to determine if you have achieved a durable platelet response, defined as having a platelet count of at least 50,000 per microliter on at least 4 out of 6 weekly measurements between week 19 and week 24.

You will complete the ITP-PAQ questionnaire again to evaluate changes in your symptoms throughout the study period.

The medical team will review all bleeding events that occurred during the study period.

Throughout the entire study period, the medical team will monitor for any bleeding events. These are classified by severity and location, including bleeding in the skin, mucous membranes, or internal organs.

The time it takes for your platelet count to first reach 50,000 per microliter will be recorded.

The number of weeks during which your platelet count remains at least 30,000 per microliter and has at least doubled from your baseline level will be counted.

The medical team will track whether you achieve a complete platelet response, which means reaching a platelet count of at least 100,000 per microliter on at least 2 visits during the study.

If you are currently taking other medications for immune thrombocytopenia, you may continue taking them during the study, provided the dose has been stable for at least 4 weeks before starting the study medication.

Permitted medications include one thrombopoietin receptor agonist (such as romiplostim, eltrombopag, avatrombopag, or hetrombopag), which helps stimulate platelet production.

You may also continue taking one oral corticosteroid given daily or every other day, at a dose not exceeding 20 milligrams of prednisone daily or an equivalent dose.

Additionally, you may continue taking fostamatinib if this was part of your treatment before joining the study.

The doses and frequency of these medications are expected to remain stable throughout the study period.

If your platelet count drops to dangerously low levels or you experience significant bleeding, you may require rescue therapy. This refers to additional emergency treatment to quickly increase your platelet count.

The medical team will record if rescue therapy is needed, when it is first required, and how often it is used during the study period.

Blood samples will be collected at specified times to measure the concentration of mezagitamab in your bloodstream.

The medical team will monitor for the development of anti-drug antibodies, which are proteins your immune system might produce in response to the medication.

If anti-drug antibodies are detected, the levels will be measured to determine if they affect how the medication works.

The medical team will also check for neutralizing antibodies, which are a specific type of anti-drug antibody that can reduce the effectiveness of the medication.