How Drug Interactions Work with Zarxio

Zarxio (Filgrastim-sndz) is a biologic medication that stimulates your bone marrow to produce more neutrophils (white blood cells). Because of how Zarxio works in your body, certain medications can interfere with its effectiveness or increase the risk of side effects.

Drug interactions happen when one medication changes how another medication works. With Zarxio, the most important interactions involve:

• Medications that affect your bone marrow
• Medications that affect your white blood cell count
• The timing of Zarxio relative to chemotherapy

Understanding these interactions helps you stay safe and get the most benefit from your treatment. Always tell your doctor about every medication, supplement, and over-the-counter product you are taking.

Major Drug Interactions

Chemotherapy drugs (critical timing interaction)

This is the most important interaction to understand. Zarxio should not be given within 24 hours before or 24 hours after receiving cytotoxic chemotherapy.

Why? Chemotherapy is designed to kill rapidly dividing cells. Zarxio stimulates your bone marrow cells to divide rapidly. If Zarxio is given too close to chemotherapy, those actively dividing bone marrow cells become more sensitive to the chemo drugs, which could cause worse damage to your bone marrow — the opposite of what you want.

Your oncologist will carefully schedule your Zarxio injections to start at least 24 hours after your last chemo dose. Follow this schedule exactly. If you are unsure about timing, call your doctor's office before giving yourself an injection.

Lithium

Lithium (used to treat bipolar disorder and other mood disorders) can increase the release of neutrophils from the bone marrow. When combined with Zarxio, which also boosts neutrophil production, the result can be an excessive increase in white blood cells — a condition called leukocytosis.

If you take Lithium, your doctor does not necessarily need to stop it, but they will likely monitor your blood counts more frequently to make sure your white blood cell count does not get too high. Always mention Lithium use to any doctor prescribing Zarxio.

Moderate Drug Interactions

Topotecan

Topotecan is a chemotherapy drug used for certain cancers. When used together with Zarxio, it can actually prolong neutropenia rather than shorten it. If your treatment plan includes Topotecan, Zarxio should not be started until at least 24 hours after Topotecan is completed. Your oncologist will manage this timing carefully.

Bleomycin

Bleomycin is a chemotherapy drug known for its potential to cause lung damage (pulmonary toxicity). There is some evidence that using G-CSF medications like Zarxio along with Bleomycin may increase the risk of lung problems. If Bleomycin is part of your chemotherapy regimen, your doctor will weigh the risks and benefits of adding Zarxio and may monitor your lung function more closely.

Supplements and Over-the-Counter Medications

While Zarxio does not have a long list of supplement interactions, there are a few things to keep in mind:

Pain relievers

Since bone pain is the most common side effect of Zarxio, many patients take over-the-counter pain medications. Both acetaminophen (Tylenol) and NSAIDs like ibuprofen (Advil, Motrin) are generally considered safe to use with Zarxio. However, always check with your doctor first, especially if you are on chemotherapy, because:

• NSAIDs can affect platelet function and may not be recommended if your platelet count is low
• Acetaminophen can mask a fever, which is an important warning sign of infection in neutropenic patients

Your oncology team will advise you on which pain reliever is safest for your specific situation.

Vitamins and supplements

There are no known direct interactions between Zarxio and common vitamins or dietary supplements. However, some supplements (like high-dose vitamin E or fish oil) can affect blood clotting, which may be a concern if your platelet counts are low from chemotherapy. Tell your doctor about all supplements you take.

Herbal products

Herbal supplements are not well-studied with biologic medications like Zarxio. Some herbs that claim to "boost the immune system" (such as echinacea or astragalus) could theoretically interact with medications that affect white blood cell production. It is best to discuss any herbal products with your doctor before using them during Zarxio treatment.

Food and Drink Interactions

The good news: Zarxio has no known food interactions. You do not need to change your diet or avoid specific foods while taking Zarxio.

That said, general nutrition advice during chemotherapy and Zarxio treatment includes:

• Stay well-hydrated — drink plenty of water throughout the day
• Eat a balanced diet — good nutrition supports your bone marrow recovery
• Practice food safety — when your white blood cell count is low, avoid raw or undercooked meat, fish, and eggs to reduce infection risk

Alcohol does not have a known direct interaction with Zarxio, but heavy alcohol use can suppress bone marrow function, which works against what Zarxio is trying to do. If you drink alcohol, discuss it with your doctor.

What to Tell Your Doctor Before Starting Zarxio

Before your first Zarxio injection, make sure your doctor knows about:

• All prescription medications — especially Lithium, chemotherapy drugs, and any other medications that affect your immune system
• Over-the-counter medications — including pain relievers, allergy medications, and cold remedies
• Vitamins and supplements — including multivitamins, herbal products, and fish oil
• Your complete medical history — especially sickle cell disease or trait, kidney problems, or a history of allergic reactions to Filgrastim or Pegfilgrastim
• Pregnancy or breastfeeding — Zarxio is Pregnancy Category C and should only be used if clearly needed

Do not start or stop any medication while taking Zarxio without talking to your doctor first. Even seemingly harmless changes can affect your treatment.

Keep a medication list

One of the best things you can do is keep an updated list of every medication, supplement, and vitamin you take — including doses and how often you take them. Bring this list to every doctor appointment and pharmacy visit. This simple step can prevent dangerous interactions and help your care team keep you safe.

If you are looking for more information about Zarxio, read our complete guide on what Zarxio is, its uses, and dosage. And if you need help finding Zarxio at a pharmacy near you, search Medfinder to check availability.