Learn about common and serious Zarxio (Filgrastim-sndz) side effects, how to manage them, and when to seek medical attention right away.
Zarxio (Filgrastim-sndz) is a biosimilar medication that helps your body produce more white blood cells called neutrophils. It is used in people undergoing chemotherapy, bone marrow transplants, or living with severe chronic neutropenia. Like all medications, Zarxio can cause side effects — but knowing what to expect can help you feel more in control of your treatment.
Most side effects from Zarxio are mild to moderate and go away on their own. However, there are some serious side effects that require immediate medical attention. This guide will walk you through both so you know exactly what to watch for.
The following side effects are the most frequently reported by patients taking Zarxio. They are usually manageable and tend to improve as your body adjusts to the medication.
Up to 30% of patients experience bone pain while taking Zarxio. This makes sense when you think about how Zarxio works — it stimulates your bone marrow to produce neutrophils at a faster rate, which can cause aching or soreness in your bones. The pain is most commonly felt in the legs, hips, lower back, and sternum (breastbone).
What helps: Over-the-counter pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can usually manage bone pain effectively. Some patients also find relief with warm compresses or gentle stretching. Talk to your doctor before taking any pain medication, especially if you are on chemotherapy.
Headaches are common during Zarxio treatment and are usually mild. Staying hydrated and getting enough rest can help. If headaches are persistent or severe, let your doctor know.
Some patients feel nauseous, especially if they are also receiving chemotherapy. Eating small, frequent meals and avoiding strong smells may help. Your doctor can also prescribe anti-nausea medication if needed.
Feeling tired is common during Zarxio therapy, particularly when combined with chemotherapy. Listen to your body and rest when you need to, but try to stay lightly active if you can.
Since Zarxio is given as a subcutaneous injection, you may notice redness, swelling, or mild pain at the injection site. Rotating your injection site (alternating between your abdomen, thighs, and upper arms) can help reduce irritation.
Arthralgia (joint pain) and myalgia (muscle pain) are related to the same bone marrow stimulation that causes bone pain. These symptoms are usually mild and respond to the same treatments.
A low-grade fever can occur with Zarxio use. However, because Zarxio is often used in people at risk for infections, any fever should be reported to your doctor promptly — it could be a sign of infection rather than a side effect of the medication.
While uncommon, Zarxio can cause serious side effects that need urgent medical attention. Call your doctor or go to the emergency room right away if you experience any of the following:
Zarxio can cause your spleen to enlarge, and in rare cases, it can rupture. This is a medical emergency. Call 911 or go to the ER immediately if you have pain in your left upper abdomen or left shoulder tip. Your doctor may monitor the size of your spleen during treatment.
ARDS is a serious lung condition that can occur with Zarxio. Seek immediate medical care if you develop sudden shortness of breath, rapid breathing, or feel like you cannot get enough air. This is more common in patients with pneumonia or other lung infections.
Although rare, some patients have allergic reactions to Zarxio. Signs include hives, swelling of the face or throat, wheezing, difficulty breathing, rapid heartbeat, or feeling faint. If you have ever had a serious allergic reaction to Filgrastim, Pegfilgrastim, or any component of Zarxio, you should not take this medication.
If you have sickle cell disease or sickle cell trait, Zarxio can trigger a sickle cell crisis, which can be very painful and potentially life-threatening. Tell your doctor about any sickle cell history before starting treatment.
This rare condition causes fluid to leak from your blood vessels into surrounding tissue. Symptoms include swelling, low blood pressure, difficulty breathing, and rapid weight gain. Contact your doctor immediately if you notice these signs.
Zarxio can rarely cause inflammation of the kidneys. Watch for dark or bloody urine, swelling in your face or legs, or decreased urine output, and report these to your doctor.
If you are receiving Zarxio alongside chemotherapy, it can be hard to tell which side effects come from Zarxio and which come from your chemo drugs. Your oncologist is experienced in sorting this out. Report all new symptoms so your care team can help.
Zarxio is approved for use in children for chemotherapy-induced neutropenia and severe chronic neutropenia. Side effects in children are similar to those in adults. Parents and caregivers should watch for bone pain, fever, and any signs of allergic reaction.
Zarxio is classified as Pregnancy Category C, meaning it should only be used during pregnancy if the potential benefit justifies the risk to the fetus. If you are pregnant, planning to become pregnant, or breastfeeding, discuss the risks and benefits with your doctor.
Long-term use of Zarxio in patients with severe chronic neutropenia has been associated with a risk of developing myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Your doctor will monitor your blood counts regularly and discuss this risk with you.
Here are practical tips to help you get through Zarxio treatment more comfortably:
Understanding potential drug interactions is also important for managing your overall treatment safely.
If you are having trouble finding Zarxio at your pharmacy, check out our guide to finding Zarxio in stock near you, or search on Medfinder to see which pharmacies have it available today.
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