Zarxio Side Effects: What to Expect and When to Call Your Doctor

Understanding Zarxio Side Effects

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.

Common Side Effects of Zarxio

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.

Bone pain (the most common side effect)

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.

Headache

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.

Nausea

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.

Fatigue

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.

Injection site reactions

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.

Joint and muscle pain

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.

Fever

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.

Serious Side Effects: When to Call Your Doctor Immediately

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:

Splenic rupture

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.

Acute respiratory distress syndrome (ARDS)

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.

Serious allergic reactions

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.

Sickle cell crises

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.

Capillary leak syndrome

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.

Glomerulonephritis

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.

Side Effects in Specific Populations

Patients on chemotherapy

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.

Children

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.

Pregnant or nursing women

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.

Patients with severe chronic neutropenia

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.

How to Manage Zarxio Side Effects

Here are practical tips to help you get through Zarxio treatment more comfortably:

• Stay ahead of bone pain. If your doctor approves, take a pain reliever like acetaminophen or ibuprofen before your injection. This can help prevent bone pain from becoming severe.
• Stay hydrated. Drinking plenty of water can help with headaches, nausea, and overall well-being during treatment.
• Rotate injection sites. Switch between your abdomen, outer thighs, and upper arms to minimize injection site reactions.
• Keep a symptom journal. Write down any side effects you notice, including when they started and how severe they are. This information is valuable for your doctor at follow-up appointments.
• Do not skip doses. Even if side effects are bothersome, do not stop taking Zarxio without talking to your doctor first. Stopping too soon can leave you vulnerable to dangerous infections. Your doctor can adjust your dose or recommend ways to manage side effects.
• Know when to call. Keep your doctor's after-hours number handy. For any of the serious side effects listed above, do not wait until your next appointment — call right away.

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.