You may have heard about Mimrylo (rusfertide), a medicine approved by the FDA to treat erythrocytosis (too many red blood cells) in adults with polycythemia vera (PV). If you have PV that has been hard to control, Mimrylo offers a new way to help keep your red blood cell levels in a healthier range.
PV is a rare, slow-growing blood cancer. With PV, your bone marrow makes too many red blood cells, which can make your blood thicker than normal. Thicker blood moves more slowly and can raise your risk of blood clots. Many people can manage PV with phlebotomy (removing blood, much like a blood donation) and sometimes other medicines, but some people still struggle to keep their levels where they should be.
Below are common questions and answers about Mimrylo for PV and whether it may be an option for you.
How Does Mimrylo Work for Polycythemia Vera?
Mimrylo contains the active ingredient rusfertide. It belongs to a group of medicines called hepcidin mimetics. This means it acts like a natural hormone in your body called hepcidin, which helps control how your body uses iron.
Your body needs iron to make red blood cells. Rusfertide blocks a “door” on your cells called ferroportin that normally lets iron move into the bloodstream. By blocking this door, Mimrylo lowers the amount of iron available to make new red blood cells. With less iron to work with, your body makes fewer red blood cells.
This helps lower your hematocrit, which is the share of your blood made up of red blood cells. The goal of the treatment is to keep your hematocrit below 45%, a level linked to a lower risk of PV-related problems. When your hematocrit stays controlled, you may need fewer phlebotomy sessions to remove blood.
While Mimrylo can help manage PV, it does not cure the condition.
How Do I Use Mimrylo?
Mimrylo is given as an injection under your skin (a subcutaneous injection), usually once a week. You can inject it into your belly (at least 2 inches from your belly button), the front of your thigh, or the outer area of your upper arm. The upper arm should be used only if a caregiver gives you the injection.
Mimrylo comes as a powder that you mix with a liquid (diluent) right before you use it. Your health care provider or a caregiver will show you how to prepare and inject it. Do not inject Mimrylo yourself until you have been shown how. A few tips to keep in mind:
- Mimrylo comes in 9.5 mg, 19 mg, 28 mg, 41 mg, and 54 mg vials. Depending on your dose, you may need more than one vial and injection. Follow your health care provider’s instructions for preparing your dose.
- After you mix it, use Mimrylo within four hours. Throw it away if it is not used within that time.
- Choose a different injection site each time. Do not inject into skin that is tender, bruised, red, irritated, hard, or broken.
- Store Mimrylo at room temperature and in its original carton to protect it from light. Do not freeze it.
Your provider will decide your dose. The recommended starting dose is 19 mg once a week. Based on your blood counts and how well you tolerate the medicine, your provider may adjust your dose anywhere from 9.5 mg to 108 mg a week to keep your hematocrit below 45%. Doses above 54 mg are given as two injections on the same day, while doses above 82 mg are split between two days of the week.
If you miss a dose, contact your health care provider or pharmacist to ask about the next steps. The directions can be different based on whether you inject once or twice a week and how long ago your dose was due.
How Was Mimrylo Studied for Polycythemia Vera?
The FDA approved Mimrylo based on a study called VERIFY. This was a phase 3, multicenter, randomized, double-blind, placebo-controlled study involving 293 adults with PV. “Double-blind” means that for the main part of the study, neither the patients nor the study investigators knew who was getting Mimrylo and who was getting a placebo (no medicine in it).
The people in the study had PV that was hard to control. To join, they needed at least three phlebotomies in the previous 28 weeks (or at least five in the past year) even though they were already getting standard treatment. Standard treatment was phlebotomy alone or phlebotomy plus one or more other medicines. People in the study had the following traits:
- The average age was 57 years, and ages ranged from 27 to 86 years.
- About 7 in 10 were male, and the rest were female.
- Most participants were White (89.4%), 3.1% were Asian, 0.7% were Black or African American, 0.7% were American Indian or Alaska Native, and the rest were of other, unreported, or unknown races; about 5% of participants identified as Hispanic or Latino.
- Their average hematocrit at the start was about 42%.
Everyone was randomly assigned to use either Mimrylo or a placebo for 32 weeks. People started Mimrylo at 19 mg once a week, and the dose was adjusted to keep their hematocrit below 45%. People who finished the first 32 weeks could enter a longer-term phase of the study where everyone received Mimrylo.
What Benefits Were Seen?
Researchers mainly looked at how many people had a “response,” which meant their condition stayed controlled enough that they did not need a phlebotomy between weeks 20 and 32. Here is what they found:
- About 77% of people using Mimrylo had a response (did not need a phlebotomy), compared with about 33% of people using the placebo.
- About 63% of people using Mimrylo kept their hematocrit below 45% during the study, compared with about 14% of people using the placebo.
- People using Mimrylo needed far fewer phlebotomies on average (about 0.5 per person) than people using the placebo (about 1.8 per person).
- People using Mimrylo also reported a small improvement in fatigue (tiredness), while people using the placebo did not.
Keep in mind that study results show what happened for a group of people. Your own results may be different.
How Long Does It Take Mimrylo to Work?
Mimrylo starts lowering the iron available in your body within about one to two days of a dose. It reaches steady levels in your system after about three weekly doses. Your red blood cell levels come down more gradually over the following weeks as your body makes fewer new red blood cells.
Your health care provider will check your blood counts with a complete blood count (CBC) test, often every two to four weeks when you first start and whenever your dose changes. These results help your provider fine-tune your dose. It may take many weeks to find the dose that keeps your hematocrit in the target range, so try to keep all of your lab appointments.
What Else Should I Know About Using Mimrylo?
If you are able to become pregnant, there are a few important things to know. Based on animal studies, Mimrylo may be harmful if used during pregnancy.
- Your provider may do a pregnancy test before you start Mimrylo.
- Use effective birth control during treatment and for at least 30 days after your final dose.
- Tell your provider right away if you become pregnant or think you may be pregnant, and stop using Mimrylo.
You should also not breastfeed during treatment and for 30 days after your final dose, as it is not known if Mimrylo passes into breast milk. Talk with your provider about the best way to feed your baby during this time.
This article does not cover the side effects of Mimrylo. To learn more, see our separate article on managing the side effects of Mimrylo.
How Do I Get Mimrylo, and Who Prescribes It?
Mimrylo requires a prescription. PV is usually managed by a hematologist, a doctor who specializes in blood conditions. Because Mimrylo is a specialty injectable medicine, your prescription may be filled through a specialty pharmacy rather than your local drugstore. This pharmacy works with you, your provider, and your insurance to fill the prescription and can mail the medicine to your home.
Is There Any Cost Assistance Available for Mimrylo?
Yes, there is cost assistance available for Mimrylo. Assistance can vary depending on your insurance. You can visit the drugmaker’s copay assistance program website or contact them by phone at 844-817-6468 to learn more.
