As reported on MedCity News, the U.S. Food and Drug Administration has approved Takeda Pharmaceutical’s Mimrylo (rusfertide) for the treatment of erythrocytosis in adults with polycythemia vera (PV), a rare blood cancer characterized by excessive production of red blood cells. The approval marks the arrival of the first therapy in a new class designed to address a key driver of the disease and may significantly alter the current treatment landscape.
Polycythemia vera is a chronic myeloproliferative neoplasm caused by acquired genetic mutations that prompt the bone marrow to overproduce blood cells. Elevated red blood cell counts thicken the blood, increasing the risk of serious cardiovascular events such as heart attack and stroke. Patients frequently experience symptoms including headaches, dizziness, and persistent fatigue.
For decades, therapeutic phlebotomy, the periodic removal of blood to lower red blood cell levels, has served as a cornerstone of disease management. Mimrylo offers a different approach by targeting the body’s iron regulation system. The therapy is an engineered peptide modeled after hepcidin, a naturally occurring hormone that controls iron availability. By limiting the amount of iron accessible for red blood cell production, the drug helps regulate excessive erythrocyte formation.
Originally developed by Protagonist Therapeutics, rusfertide was designed to overcome the limitations of native hepcidin, which is not well suited as a therapeutic agent due to challenges involving stability, solubility, and potency. The company used its peptide-engineering platform to create a version capable of functioning effectively as a once-weekly injectable treatment.
The FDA decision was supported by data from a pivotal Phase 3 trial evaluating patients with uncontrolled erythrocytosis who required regular phlebotomies. Results demonstrated that nearly 77% of patients receiving rusfertide avoided the need for therapeutic phlebotomy through 32 weeks, compared with about 33% of those receiving placebo. The most frequently reported side effects included injection-site reactions and anemia.
Hematology experts believe the new therapy could have a meaningful impact on clinical practice. Because phlebotomy remains a routine intervention for many PV patients, a treatment capable of reducing or eliminating that requirement may improve long-term disease management and patient quality of life.
Although several therapies are already available for polycythemia vera, treatment options remain limited. Incyte’s Jakafi is approved for patients who do not respond adequately to hydroxyurea, while PharmaEssentia’s Besremi is used in the first-line setting. However, interferon-based therapies such as Besremi may not be suitable for certain individuals, including those with autoimmune disorders or a history of mood disorders, leaving a need for additional treatment alternatives.
Notably, the FDA approval for Mimrylo does not restrict its use to a specific line of therapy. The broad label could allow physicians greater flexibility when determining how and when to incorporate the drug into treatment strategies for eligible patients.
The approval also represents a major commercial milestone for both Takeda and Protagonist. In 2024, Takeda entered into a partnership with Protagonist, providing an upfront payment of $300 million to jointly develop the therapy. Earlier this year, Protagonist elected to exchange its U.S. profit-sharing rights for milestone payments and royalties, securing substantial near-term funding while retaining future financial upside tied to the drug’s success.
Takeda now holds exclusive worldwide commercialization rights for Mimrylo and has identified the therapy as a potential blockbuster product. Analysts have projected annual sales could eventually approach $2 billion, helping strengthen Takeda’s hematology portfolio as the company prepares for revenue pressure from upcoming patent expirations affecting some of its largest products.
The company has set a list price of $4,200 per vial. Based on weekly dosing, the annual cost of treatment is approximately $218,400. Mimrylo is now commercially available, while long-term follow-up investigations from the pivotal study continue. Takeda has indicated that additional clinical data will be presented at future medical meetings and that efforts are underway to pursue approvals in markets outside the United States.
