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

Releuko (filgrastim-ayow) is an effective medication for preventing and treating neutropenia, but like all biologic medications, it can cause side effects. Most are manageable and temporary. A small number are serious and require immediate medical attention. Knowing the difference can help you stay on therapy safely and give you peace of mind during treatment.

Most Common Side Effect: Bone and Muscle Pain

The most frequently reported side effect of Releuko — and all filgrastim products — is bone pain (medically called "ossalgia" or "arthralgia"). This happens because Releuko works by stimulating your bone marrow to produce more white blood cells. As the marrow ramps up production, patients often feel an aching, deep pain in their bones, particularly in the:

Lower back and hips (most common)

Sternum (breastbone)

Long bones (arms and legs)

Bone pain typically begins 1–2 days after starting Releuko and often peaks around the same time as maximum white blood cell production. For most patients, the pain resolves on its own once the drug is stopped or the dose is reduced. Over-the-counter pain relievers like acetaminophen (Tylenol) or loratadine (Claritin — an antihistamine that also reduces G-CSF-related bone pain in some patients) are often recommended. Always ask your oncologist before taking any OTC medication.

Other Common Side Effects

Depending on the condition being treated, other common side effects reported with Releuko include:

Pyrexia (fever) — Common in patients receiving it after chemotherapy; may be difficult to distinguish from chemotherapy-related fever

Rash — Skin reactions including redness and itching

Cough and shortness of breath — Report persistent respiratory symptoms to your doctor

Epistaxis (nosebleeds) — Particularly noted in AML patients

Alopecia (hair loss) — Noted in severe chronic neutropenia patients on long-term therapy

Diarrhea and nausea

Anemia — Low red blood cell count, which may be compounded by chemotherapy effects

Injection site reactions — Redness, bruising, or swelling at the injection site

Serious Side Effects — Seek Immediate Care

A small number of patients experience serious adverse events. These require immediate medical evaluation. Call your doctor or go to the emergency room if you experience:

Left upper abdominal pain or shoulder pain — These may be signs of splenic enlargement or splenic rupture, a rare but potentially fatal complication of filgrastim therapy. Do not wait — go to the ER.

Fever with lung symptoms (cough, difficulty breathing, low oxygen) — May indicate acute respiratory distress syndrome (ARDS), a rare but serious complication.

Signs of allergic reaction — Hives, swelling of lips/tongue/throat, difficulty swallowing, rapid heartbeat, or drop in blood pressure may indicate anaphylaxis. Call 911 immediately.

Blood in urine or swelling — May indicate glomerulonephritis (kidney inflammation), a rare but documented complication.

Severe pain episodes in sickle cell patients — Filgrastim products can trigger life-threatening sickle cell crises in patients with sickle cell disease. Releuko should generally be avoided in these patients.

Long-Term Use Considerations for Chronic Neutropenia

Patients with severe chronic neutropenia (SCN) who take Releuko long-term require ongoing monitoring. Studies show that long-term use of G-CSF products in congenital neutropenia patients is associated with a risk of developing myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) — though this risk appears confined to the SCN population and is related to the underlying disease rather than the drug alone. Your hematologist will monitor your complete blood count (CBC) with differential and platelet counts regularly: every 1–2 weeks during the first month, then monthly, then less frequently once stable.

What to Tell Your Doctor Before Starting Releuko

Always tell your doctor if you have:

A history of allergic reaction to filgrastim or pegfilgrastim — this is a contraindication

Sickle cell disease

Kidney disease

Are pregnant, planning to become pregnant, or breastfeeding

For more on drug interactions to watch for, read our guide on Releuko drug interactions. And if you need help finding Releuko in stock, visit medfinder.com.