Mimrylo (rusfertide) is used to treat erythrocytosis (too many red blood cells) in adults with polycythemia vera (PV). It helps keep your red blood cell levels in a healthy range, which may lower how often you need a phlebotomy (blood draw).
Like most medicines, Mimrylo may cause side effects, some of which are more common than others. Some Mimrylo side effects may improve as your body adjusts to treatment.
Keep reading to learn about common side effects of Mimrylo, what you can do to prevent them, what to do if they happen, and when to tell your health care provider.
This article does not include all possible side effects of Mimrylo. Tell your health care provider if you have side effects that are ongoing or bother you, even if they are not listed.
Common Mimrylo Side Effects
The most common side effects reported in clinical studies include:
- Injection site reactions (redness, itching, pain, or swelling where you inject)
- Low red blood cell count (anemia)
- Shortness of breath
- Increased platelet count (a blood cell that helps your blood clot)
In most cases, injection site reactions are mild and often improve over time. Other side effects, such as anemia and higher platelet counts, are usually managed with regular blood tests and dose changes. Contact your health care provider if you have symptoms that feel severe or do not improve. Do not stop taking Mimrylo unless your provider recommends it.
Serious Side Effects of Mimrylo
Less common but potentially serious side effects of Mimrylo may include:
- New or worsening high platelet counts (thrombocytosis), which may raise the risk of blood clots or bleeding
- Severe injection site reactions
- Severe allergic reactions
If you think you may be having a serious side effect, contact your health care provider right away. In some cases, severe symptoms may require urgent medical care. If your symptoms feel severe or life-threatening, call 911 or go to the nearest emergency room right away.
Tips for Managing Mimrylo Side Effects
Some side effects can be managed in simple ways. The sections below explain common Mimrylo side effects and what you can do to help prevent or relieve them.
1. Injection site reactions
Injection site reactions are the most common side effect of Mimrylo. In clinical studies, nearly half of people had a reaction where they injected the medicine. The most common types of reactions were redness, itching, pain, and swelling. Most reactions were mild to moderate, and only a small number of people (less than 1%) stopped treatment because of them.
Possible symptoms include:
- Redness or discoloration
- Itching
- Pain or tenderness
- Swelling
- Bruising or hardening of the skin at the injection site
Mild reactions often get better on their own. Here are some strategies that may help:
- Apply an ice pack to the area to ease pain and swelling.
- Ask your provider about using a topical corticosteroid (steroid) cream, an antihistamine, or a pain reliever (analgesic) as needed.
- Rotate your injection sites, and do not inject into the same spot twice in a row.
- Do not inject into skin that is tender, bruised, red, irritated, hard, or broken.
- Inject at least 2 inches away from your belly button when using your stomach for injections.
Tell your health care provider if an injection site reaction is severe, spreads, or does not go away.
2. Low red blood cell count (anemia)
Anemia means you have fewer red blood cells or less hemoglobin than normal. It is a common side effect of Mimrylo and also an expected one, as the medicine works by lowering the iron your body uses to make red blood cells. In studies, about 16% of people developed anemia, making it the most common reason for lowering the dose; about 1 in 10 people had to lower the dose due to anemia, but very few had to stop the medicine.
Possible symptoms include:
- Tiredness or weakness
- Pale skin
- Shortness of breath
- Dizziness or lightheadedness
Here are some ways to manage anemia:
- Keep your lab appointments so your provider can check your blood counts and catch anemia early.
- Rest when you need to, and pace your activities on days you feel more tired.
- Tell your provider if your tiredness worsens or you have new symptoms such as shortness of breath or dizziness.
Your provider may lower your dose of Mimrylo if your anemia becomes significant. Do not change or stop your dose on your own.
3. New or worsening high platelet counts (thrombocytosis)
Mimrylo may raise your platelet count. In studies, platelet counts rose by about 31% on average within the first four weeks of treatment and generally leveled off by around week 8. Platelets are cells that help your blood clot, but very high levels can add to the risk of blood clots or bleeding, so this is an important side effect to watch for. Your provider will check your blood counts (CBC) every two to four weeks, or as needed.
If your platelets rise too high, your provider may change your Mimrylo dose, stop treatment, or start another medicine to lower your platelet count.
Call your provider right away or seek emergency care if you notice signs of a blood clot or bleeding, such as:
- Chest pain
- Shortness of breath
- Pain or swelling in a leg
- A sudden, severe headache
- Unusual bruising or bleeding
Frequently Asked Questions About Mimrylo Side Effects
Can Mimrylo cause long-term side effects?
Clinical studies did not identify specific long-term side effects unique to Mimrylo. The main ongoing effects are the ones listed above, such as injection site reactions, anemia, and higher platelet counts, which your health care provider monitors with regular blood tests and manages with dose changes. In the studies, some people took Mimrylo for more than two years. Talk to your provider about what to expect with long-term use.
Does Mimrylo cause weight gain or hair loss?
Weight gain and hair loss were not reported as side effects of Mimrylo in clinical studies. As with any medicine, tell your health care provider about any new or unexpected symptoms so they can help figure out the cause.
Reducing Your Risk of Mimrylo Side Effects
To lower your risk of side effects:
- Take Mimrylo exactly as prescribed.
- Follow the instructions for preparing and injecting it, including rotating your injection sites and using the medicine within four hours after mixing.
- Keep all of your lab appointments so your provider can check your blood counts.
- Keep track of any new or changing symptoms and share them with your health care provider.
- Tell your health care provider about side effects that do not improve or start to interfere with daily activities.
Your health care provider can help you decide whether changes to your treatment plan are needed.
