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Filgrastim (Zarxio)


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What Is Filgrastim (Zarxio)?

Filgrastim (pronounced [fil GRA stim]) is also known by the brand name Neupogen. Other available biosimilars include Zarxio, Granix, and Nivestym. Neupogen was the first medication produced based on the active element, filgrastim. These drugs have been used successfully for cancer patients to stimulate the growth of white blood cells. Based on Neupogen, Zarxio became the first biosimilar product available in the United States in March 2015. Thus, Zarxio is similar to Neupogen in its mechanism of action, administration route, strength, and dosage. The difference between the formulation of the two agents is in one inactive component.

What Is a Biosimilar?

A biosimilar drug is a low-cost alternative to a biologic medicine that is similar but not identical to the original medicine. There is no clinical difference. Biosimilars are similar to the FDA-approved medicines in their potency, purity, safety, and efficacy and can be used interchangeably.

Mechanism of Action

Filgrastim is called a hematopoietic agent and is used to treat neutropenia. Filgrastim is not a hazardous drug, nor is it a form of chemotherapy. It is, however, a blood cell colony-stimulating agent (CSA) which aids in the production of white blood cells (especially neutrophils) directly from the bone marrow.

What Is Neutropenia?

Neutropenia occurs when you have too few neutrophils, a type of white blood cell that helps our bodies fight off infections. Having neutropenia indicates a higher risk of developing serious bacterial and fungal infections. Neutropenia is a very common side effect for cancer patients undergoing chemotherapy.

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How Is Zarxio Used?

Filgrastim has been approved by the Food and Drug Administration (FDA) for the treatment of severe long-standing neutropenia and neutropenia caused by chemotherapy. It has also been approved for use prior to and after a stem cell or bone marrow transplantation, and for patients with acute myeloid leukemia (AML) on induction chemotherapy.

Available Formulations

Zarxio is only available as injections given subcutaneously (under the skin) or intravenously (IV). Zarxio is available as a single-use prefilled syringe for subcutaneous injection in two doses: 300 mcg/0.5 ml and 480 mcg/0.8 ml.

IV Infusion

The IV infusion can be administered by a healthcare provider or caregiver as a short infusion over 15 to 30 minutes. It can also be administered as a continuous infusion or as a longer infusion of no more than 24 hours.

Subcutaneous Injection

The injection sites can include upper areas of the buttocks, front of the thighs, lower abdomen area (2 inches away from the navel), or the upper outer arms. Do not inject into areas where the skin is tender, bruised, red, scaly, or hard, and avoid areas with scars or stretch marks. After injection, do not rub the injection site. Do not handle the prefilled syringe if you are allergic to latex, and do not save unused medication in the prefilled syringe for later use.

You should not attempt to give yourself a subcutaneous injection until you have received the appropriate training from your healthcare provider. 

Missed Dose

If you miss a dose, contact your physician immediately to reschedule.


Store Zarxio in the refrigerator and avoid freezing. If frozen, thaw in the refrigerator before use. Zarxio should be thawed (taken out of the refrigerator) at room temperature for 30 minutes before use. It can be left at room temperature for up to 24 hours. Do not shake the vials and keep them protected from light by storing them in their original containers.

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Dispose of Zarxio if it has been frozen more than once. Dispose of Zarxio if it has been left at room temperature for more than 24 hours. After injection, dispose of any unused Zarxio left in the prefilled syringe. Be sure to dispose of the pre-filled syringes in an FDA-cleared sharps disposal container (not in the household trash).

What To Avoid While Taking Filgrastim

While on the Filgrastim therapy, you must follow some precautions. Always tell your physician about any medication you are already taking. Do not take any drug or medicine (even herbals or over-the-counter medications) without prior consent from your physician or pharmacist, as they may have interactions with Zarxio. Avoid taking Zarxio within 24 hours before or 24 hours after having chemotherapy. 

Pregnancy and Zarxio

Pregnant women, women who are planning to become pregnant, and breastfeeding women must consult a physician prior to initiating Zarxio. The risk to the fetus or baby is unknown.

Side Effects

As with any other medication, you may encounter side effects while taking Filgrastim. A few things to keep in mind are:

  • You may not have all the side effects listed below. Many people may experience little to no side effects.
  • The severity of side effects may vary from person to person, so do not compare your side effects with other people’s experiences.
  • Most of the side effects will improve when therapy is discontinued.
  • Do not hide any symptoms; when you feel any discomfort, do not hesitate to tell your physician or pharmacist about it.

Note: The side effects listed below are not a comprehensive list of all side effects. Talk to your doctor if you have questions. 

Some of the more serious side effects of Zarxio are:

Bone and Muscle Aches

This is the most common side effect of Zarxio since it stimulates the bone marrow (a spongy substance found inside of bone), causing it to swell, resulting in potential bone pain. It commonly starts about 1 to 2 days after receiving a Zarxio dose and can last up to a week, depending on the person.

Bone or muscle pains can be controlled using over-the-counter painkillers like Tylenol or Motrin. Consult your doctor or pharmacist before starting any new over-the-counter therapies.

Thrombocytopenia, Leukocytosis

It is essential to keep up with regular blood tests, especially the complete blood count test (CBC). The CBC blood test is capable of detecting potential side effects of Zarxio, including leukocytosis (high white blood cells level) and thrombocytopenia (low platelet count). Contact your physician if any unusual bleeding or bruising occurs.

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Lung Problem Called Acute Respiratory Distress Syndrome (ARDS)

Contact a physician or get emergency medical help right away if you have shortness of breath with or without a fever, trouble breathing, or a fast rate of breathing.

Kidney Injury

Call your doctor right away if you experience puffiness in your face or ankles, blood in your urine, or brown-colored urine. Also, contact your doctor if you notice you urinate less than usual.

Capillary Leak Syndrome

Zarxio can cause fluid to leak from blood vessels into your body’s tissues. Capillary leak syndrome (CLS) can quickly cause you to have symptoms that may become life-threatening. Get emergency medical help right away if you develop any of the following symptoms: swelling or puffiness, urinating less often, trouble breathing, swelling of the abdominal area, and feeling of fullness, dizziness, or faintness.

Inflammation of Blood Vessels

Contact your physician if you develop purple spots or redness on your skin.

Rupture of the Spleen

A ruptured spleen is one of the most severe side effects of Zarxio. The spleen may become enlarged and may possibly rupture, which can be fatal. Call your doctor right away if you have pain in the upper left stomach (abdomen) or your left shoulder.

Less severe side effects can include:

  • Dizziness
  • Cough
  • Fatigue
  • Headache
  • Nausea
  • Fever

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Unless approved by your physician, Filgrastim is generally not recommended in: 

  • Patients who have an allergy to human granulocyte colony-stimulating factors (CFS) such as filgrastim or pegfilgrastim products: Allergic reactions can cause a rash over the whole body, shortness of breath, wheezing, dizziness, swelling around your mouth or eyes, fast heart rate, and sweating. If you have any of these symptoms, stop using Zarxio, and call your doctor or get emergency help right away.
  • Patients with sickle cell disorder: Using Zarxio can lead to a condition called sickle cell crisis, which may be life-threatening.
  • Patients receiving radiation therapy: Zarxio may increase the risk of developing a precancerous condition called myelodysplastic syndrome (MDS) or a type of blood cancer called acute myeloid leukemia (AML).


Is Zarxio a chemo agent?

No, it is not a chemotherapy agent. Instead, it helps treat a major side effect of chemotherapy called neutropenia (low white blood cell count). Chemotherapy drugs are directed at combating your cancer cells, while Zarxio is designed to combat the after-effects of a chemotherapy session.

Does Zarxio have a different name?

Yes, it is the biosimilar of Filgrastim. Neupogen is the brand name of Filgrastim. Other biosimilars available are called Granix and Nivestym.

How is Zarxio taken?

Zarxio is only available as an injection. It can be injected subcutaneously (under the skin) or intravenously (IV). You should not attempt to give yourself a subcutaneous injection until you have received the appropriate training from your healthcare provider.


Filgrastim. In: Lexi-drugs online [database on the Internet]. Hudson (OH): Lexicomp, Inc.; 2016 [updated 30 Oct 2021; cited 4 Nov 2021]. Available from:

Filgrastim. In: In Depth Answers [database on the Internet]. Greenwood Village (CO): IBM Corporation; 2017 [cited 2021 Nov 4]. Available from:

ZARXIO® (Filgrastim) | Official Patient Website. (n.d.). Retrieved November 4, 2021, from

Zarxio: Uses, dosage, side effects, warnings. (n.d.). Retrieved November 4, 2021, from

This information is not a substitute for medical advice or treatment. Talk to your doctor or healthcare provider about your medical condition prior to starting any new treatment. AmeriPharma™ Specialty Care assumes no liability whatsoever for the information provided or for any diagnosis or treatment made as a result, nor is it responsible for the reliability of the content. AmeriPharma™ Specialty Care does not operate all the websites/organizations listed here, nor is it responsible for the availability or reliability of their content. These listings do not imply or constitute an endorsement, sponsorship, or recommendation by AmeriPharma™ Specialty Care. This webpage may contain references to brand-name prescription drugs that are trademarks or registered trademarks of pharmaceutical manufacturers not affiliated with AmeriPharma™ Specialty Care.

Dr. Dania Jaradat, PharmD was born and raised in Torrance, California. She graduated from Marshall B. Ketchum University. The most rewarding part of her job is to keep the line between pharmacist and patient open and to educate patients on medication management. In her free time, she enjoys traveling to different countries, spending time with her husband and son, and reading. See Author Biography

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