Releuko Drug Interactions: What to Avoid and What to Tell Your Doctor

Releuko (filgrastim-ayow) is a targeted biologic medication, but it doesn't work in isolation. Like all medications, it can interact with other drugs you're taking. Some interactions are timing-related (you must space out when you take them), while others are absolute contraindications. Understanding these interactions helps you stay safe and ensures your treatment works as intended.

The Most Critical Interaction: Cytotoxic Chemotherapy

The most important drug interaction for Releuko — and the one most oncologists are careful about — is with cytotoxic (cell-killing) chemotherapy drugs. The timing rule is:

Do NOT give Releuko within 24 hours before or after cytotoxic chemotherapy.

Why? Chemotherapy works by targeting rapidly dividing cells. If you take Releuko right before or during chemo, it causes your bone marrow to rapidly produce more white blood cells — which are exactly the type of actively dividing cells that chemotherapy also kills. The result is a larger pool of vulnerable cells in the path of the chemotherapy, which can worsen bone marrow suppression rather than helping it.

In clinical practice, Releuko is typically started at least 24 hours after the final chemotherapy dose in a cycle and discontinued at least 24 hours before the next chemotherapy administration begins.

Radiation Therapy

The package insert for Releuko advises avoiding simultaneous use with radiation therapy. The same principle applies: radiation targets rapidly dividing cells, and Releuko stimulates bone marrow cells to divide rapidly. The combination may amplify bone marrow toxicity. If you are receiving concurrent radiation and need G-CSF support, your oncologist and radiation oncologist should coordinate timing carefully.

Lithium

Lithium (used for bipolar disorder) is known to stimulate the release of neutrophils from the bone marrow. When taken together with Releuko, this effect may be additive — leading to higher-than-expected white blood cell counts (leukocytosis). If you take lithium and are prescribed Releuko, your oncologist should monitor your CBC more frequently. Very high neutrophil counts (above 100,000 cells/mm³) can have their own complications.

Bleomycin

Some case reports suggest that combining G-CSF products with bleomycin (a chemotherapy agent used in lymphoma treatment) may increase the risk of pulmonary toxicity (lung damage). This is not a definitive contraindication, but it's a concern your oncologist should be aware of if your regimen includes bleomycin.

Other G-CSF Products

You should not take Releuko simultaneously with another G-CSF product (Zarxio, Nivestym, Neupogen, Neulasta, or pegfilgrastim biosimilars). There is no clinical benefit to combining G-CSF agents, and the risk of excessive neutrophil stimulation (extreme leukocytosis) and associated complications rises with combination therapy.

Medications That Should Be Disclosed to Your Doctor

Because your complete blood count will be monitored throughout Releuko therapy, any medication affecting blood cell production or immune function is relevant. Tell your oncologist about:

All chemotherapy drugs — the timing interaction is critical

Immunosuppressants (methotrexate, cyclosporine, tacrolimus) — common in BMT and autoimmune patients

Corticosteroids (prednisone, dexamethasone) — may affect WBC counts independently

Lithium — as described above

NSAIDs (ibuprofen, naproxen) — can affect platelet function and kidney function, which may complicate monitoring

Any over-the-counter supplements or herbal products — some (like Echinacea) may stimulate immune function and have unpredictable interactions

Monitoring for WBC Spikes

One of the most important safety checks during Releuko therapy is monitoring for leukocytosis — an excessive rise in white blood cells (WBC count above 100,000/mm³). If your WBC count climbs too high, your doctor may reduce the Releuko dose, delay a dose, or stop treatment temporarily. This is why CBCs are checked regularly throughout G-CSF therapy.

A Note on Pregnancy and Breastfeeding

There is limited data on Releuko use in pregnancy and breastfeeding. Animal studies have shown potential risks at high doses. Tell your doctor immediately if you are pregnant, planning to become pregnant, or breastfeeding. Your oncologist and obstetrician will weigh the risks and benefits for your specific situation.

For a full overview of Releuko side effects, see our article on Releuko side effects: what to expect and when to call your doctor. And if you need help finding Releuko in stock, visit medfinder.com.