Efficacy and Safety Evaluation of Efgartigimod Alfa in Adults with Primary Immune Thrombocytopenia: A Phase 3 Randomized, Double-Blind, Placebo-Controlled Study

The primary objective of this study is to evaluate the **efficacy** of efgartigimod IV compared with placebo IV in the extent of disease control in adult participants with **Primary Immune Thrombocytopenia (ITP)**. This is clinically relevant as effective disease control can significantly improve patient outcomes by reducing the risk of bleeding and other complications associated with low platelet counts.

Secondary objectives include:

• Evaluating the efficacy of efgartigimod IV compared with placebo IV in achieving sustained platelet count response.
• Assessing the overall platelet count response to efgartigimod IV versus placebo IV.
• Evaluating the incidence and severity of bleeding in participants treated with efgartigimod IV compared to those receiving placebo IV.
• Assessing the use of rescue ITP therapy in participants treated with efgartigimod IV versus placebo IV.
• Evaluating the long-term efficacy of efgartigimod IV, including the open-label treatment period (OLTP1).
• Assessing the tolerability and safety of efgartigimod IV.
• Evaluating the immunogenicity of efgartigimod IV.
• Assessing the pharmacokinetics (PK) and pharmacodynamics (PD) of efgartigimod IV.

The clinical trial involves a total of **19 participants** diagnosed with **Primary Immune Thrombocytopenia (ITP)**. The study population includes both male and female subjects, aged 18 years and older, who have provided informed consent. Participants were selected based on specific criteria, including a documented baseline mean platelet count of less than 30 x 10^9/L and a history of ITP lasting more than 12 months. Additionally, participants must have previously undergone treatment with at least one ITP therapy, such as corticosteroids or intravenous immunoglobulin, and demonstrated an insufficient response to these treatments. The trial population includes individuals who have shown a prior response to ITP treatments, evidenced by a platelet count of at least 50 x 10^9/L within the past three years. The study does not specify any particular lifestyle considerations such as diet or physical activity. The trial includes a vulnerable population, ensuring a comprehensive evaluation of the efficacy of efgartigimod IV compared to placebo IV in disease control.

The clinical trial is designed as a **randomized**, **double-blind**, **placebo-controlled** study with a parallel-arm structure, followed by an open-label phase. The primary objective is to evaluate the efficacy and safety of **efgartigimod alfa** administered intravenously in adult participants diagnosed with **primary immune thrombocytopenia** (ITP). The trial is expected to commence recruitment on February 1, 2025, and conclude by May 17, 2028. Participants will be randomly assigned to receive either the active treatment, Vyvgart 20 mg/mL concentrate for solution for infusion, or a placebo, both administered via **intravenous use**.

The study will involve several key visits, beginning with an inclusion (screening) visit to assess eligibility based on criteria such as age, baseline platelet count, and prior treatment history. Participants must be at least 18 years old and have a documented baseline mean platelet count of less than 30 x 10^9/L. The trial will include multiple follow-up visits to monitor platelet counts and assess the primary endpoint, which is the extent of disease control defined by the number of cumulative weeks with platelet counts of at least 50 x 10^9/L during the double-blinded treatment period (DBTP).

Secondary endpoints will evaluate various aspects of platelet count response, including the proportion of participants achieving specific platelet count thresholds at designated study weeks, time to response, and the incidence of adverse events. The study will also assess the occurrence rate of rescue ITP therapy and the incidence and severity of bleeding using the ITP Bleeding Scale. Participants will be involved in the study for a maximum treatment period of 128 weeks, with conditions for early termination including withdrawal of consent, adverse events, or lack of efficacy as determined by the investigator.

The end-of-study visit will conclude the participant's involvement, during which final assessments will be conducted to evaluate the overall safety and efficacy of the treatment. The trial's design ensures rigorous monitoring and data collection to support the evaluation of efgartigimod alfa's therapeutic potential in managing primary immune thrombocytopenia.

The clinical trial involves the administration of **efgartigimod alfa**, marketed under the name Vyvgart, which is a **concentrate for solution for infusion**. This experimental medication is formulated as a solution for infusion and is administered via the **intravenous route**. The dosage is calculated based on the participant's body weight, with a maximum daily dose of 10 mg/kg and a total maximum dose of 1280 mg. The treatment period extends up to 128 days. Efgartigimod alfa is a recombinant protein, specifically an anti-FcRn receptor human monoclonal IgG1 Fc fragment, also known as ARGX-113. The pharmaceutical product is manufactured by Argenx BV and is designated as an orphan drug for the treatment of primary immune thrombocytopenia.

The study also includes a **placebo** group, which receives a placebo for efgartigimod. The placebo is designed to match the experimental treatment in appearance and administration method but does not contain the active substance. The placebo is used to maintain the double-blind nature of the trial, ensuring that neither the participants nor the investigators know which treatment is being administered. This allows for an unbiased comparison of the efficacy and safety of efgartigimod alfa against the placebo in controlling the disease.

The efficacy of **efgartigimod alfa** in the treatment of Primary Immune Thrombocytopenia (ITP) will be assessed through a Phase 3, multicenter, randomized, double-blinded, placebo-controlled, parallel-arm study. The primary endpoint for evaluating efficacy is the extent of disease control, defined as the number of cumulative weeks during the Double-Blinded Treatment Period (DBTP) with platelet counts of at least 50 × 10⁹/L. Secondary endpoints include various measures of platelet count response, such as the proportion of participants achieving platelet counts of at least 50 × 10⁹/L for specified durations and timepoints, time to response, and overall platelet count response.

Data collection will occur at multiple study visits, with specific timepoints including weeks 13 to 24 of the DBTP. The study will also assess the incidence and severity of bleeding using the ITP Bleeding Scale (IBLS), as well as the occurrence rate of rescue ITP therapy. Laboratory safety measurements, vital signs, and physical examinations will be conducted to monitor safety alongside efficacy. The study will also evaluate the incidence and prevalence of antidrug antibodies (ADA) and neutralizing antibodies (NAb) against efgartigimod in serum over time, as well as pharmacokinetic parameters such as Cmax and Ctrough. Percent change from baseline in total IgG levels in serum will also be measured over time.