The FDA has approved rusfertide (Mimrylo), the first hepcidin-mimetic therapy for adults with polycythemia vera (PV) whose disease is not adequately controlled with existing treatments. This approval introduces a subcutaneous, self-injected agent that significantly reduces the need for therapeutic phlebotomy, a longstanding treatment burden, while improving hematocrit control in a disease defined by red blood cell overproduction and raised cardiovascular risk.
Understanding Polycythemia Vera and the Need for Rusfertide
PV is a chronic myeloproliferative disorder characterized by excessive red blood cell production. This overproduction thickens the blood, increasing the risk of blood clots, stroke, and heart attack. The primary goal of managing PV is to keep hematocrit, the proportion of red blood cells in the blood, below 45% to mitigate these cardiovascular risks. This often involves repeated phlebotomy, a process that can be time-consuming, tying patients to the healthcare system, and poorly tolerated by some.
Rusfertide, a first-in-class peptide, mimics hepcidin, a hormone that naturally regulates iron in the body. By limiting the iron available to make new red blood cells, rusfertide curbs their overproduction and helps maintain red blood cell levels under control. This mechanism of action provides a novel approach to managing PV, addressing the root cause of the disease rather than just the symptoms.
VERIFY Trial Results Support Rusfertide’s Efficacy
The approval was backed by the VERIFY trial, a multicenter, randomized, double-blind, placebo-controlled phase 3 study involving 293 adults with PV. Patients requiring frequent phlebotomies despite ongoing standard care were randomized to receive rusfertide or placebo over 32 weeks. The starting dose of rusfertide was 19 mg administered subcutaneously once weekly, which was titrated to maintain hematocrit below 45%.
Key findings included: 76.9% of rusfertide patients had no phlebotomies and didn’t meet phlebotomy criteria between weeks 20 and 32, compared to 32.9% on placebo (P < .0001). This indicates a significant reduction in the need for therapeutic phlebotomy with rusfertide treatment. Rusfertide also significantly improved patient-reported fatigue, with more patients experiencing a clinically meaningful improvement in fatigue (58.7% vs 39.7%; P = .03). Additionally, rusfertide led to a statistically significant improvement in the total symptom score (P = .03).
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In terms of hematocrit control, 62.6% of rusfertide patients maintained their hematocrit below 45% throughout the 32-week period, compared to only 14.4% of patients on placebo (P < .0001). This demonstrates rusfertide's effectiveness in keeping red blood cell levels under control, a critical aspect of managing PV and reducing cardiovascular risks.
The most common side effects were injection site reactions and anemia. Injection site reactions occurred in 55.9% of rusfertide patients compared to 32.9% on placebo, while anemia was reported in 15.9% of rusfertide patients and 4.1% of placebo patients. Serious adverse events were rare, occurring in 3.4% of rusfertide patients and 4.8% of placebo patients, and none were considered related to rusfertide. This suggests that rusfertide is generally well-tolerated, with a safety profile similar to that of placebo.
Pharmacists play a key role in the management of PV, particularly with the introduction of rusfertide. They are key in counseling patients on subcutaneous injection techniques, including site rotation to minimize injection site reactions. Pharmacists also need to educate patients on recognizing signs of anemia, as rusfertide’s iron-restricting mechanism can lead to anemia in some patients. Additionally, pharmacists should provide adherence support and reinforce the importance of ongoing hematocrit monitoring during titration, as this is vital for maintaining optimal rusfertide dosing.
Rusfertide does not replace the benefits of cytoreductive therapy but can be used in conjunction with it when needed. In the VERIFY study, around half of the patients continued their standard-of-care cytoreductive agents while receiving rusfertide. This suggests that rusfertide could be an alternative for patients who are solely receiving cytoreductive therapy to avoid phlebotomies. Furthermore, rusfertide could allow for more optimal dosing of cytoreductive therapies, potentially reducing their adverse effects at higher dose levels.
