Filgrastim
Granulocyte Colony Stimulating Factor; GCSF; recombinant methionyl human GCS-F
Also known as: Neupogen · Filgen · Granulen · Granulokine · Neulasta · Neutromax · granulocyte colony-stimulating factor · GCSF · recombinant methionyl human GCS-F · r-metHuG-CSF · rhG-CSF
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive therapy of neutropenia (secondary to drug induced aplastic pancytopenia) | 5 micrograms/kg SC daily | SC | daily | Pulse therapy of no more than 5 days | 🌎 NA |
| Neutropenia | 1-5 micrograms/kg SC daily | SC | daily | Pulse therapy of no more than 5 days | 🌎 NA |
| Neutropenia | 100,000-500,000 IU (1-5 micrograms)/kg | SC | q24h | 3-5 days | 🌍 EU |
- Adjunctive therapy of neutropenia (secondary to drug induced aplastic pancytopenia): To avoid autoantibody formation, pulse therapy is recommended.
- Neutropenia: To avoid autoantibody formation, pulse therapy is recommended.
- Neutropenia: Neutrophil counts typically rise within 24 hours.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Neutropenia secondary to drug toxicity, infectious diseases, FeLV associated cyclic neutropenia or idiopathic causes | 5 micrograms/kg SC twice daily | SC | twice daily | Pulse therapy of no more than 5 days | 🌎 NA |
| Neutropenia | 1-5 micrograms/kg SC daily | SC | daily | Pulse therapy of no more than 5 days | 🌎 NA |
| Adjunctive therapy of neutropenia | 5 micrograms/kg SC daily until neutrophil count exceeds 3,000/mcl for 2 days | SC | daily | Until neutrophil count exceeds 3,000/mcl for 2 days (ideally ≤ 5 days) | 🌎 NA |
| Neutropenia | 100,000-500,000 IU (1-5 micrograms)/kg | SC | q24h | 3-5 days | 🌍 EU |
- Neutropenia secondary to drug toxicity, infectious diseases, FeLV associated cyclic neutropenia or idiopathic causes: Cost and/or development of antibodies usually limit usefulness to a few weeks, but often it is effective for acute or lifethreatening neutropenia.
- Neutropenia: To avoid autoantibody formation, pulse therapy is recommended.
- Adjunctive therapy of neutropenia: To avoid autoantibody formation, pulse therapy is recommended.
- Neutropenia: Neutrophil counts typically rise within 24 hours.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Filgrastim is a recombinant human granulocyte colony-stimulating factor (G-CSF) utilized in veterinary medicine to stimulate the bone marrow to produce neutrophils.
Key clinical points:
- Primary Indication: Used for severe, life-threatening neutropenia (e.g., secondary to parvovirus, chemotherapy-induced myelosuppression, or feline leukemia virus-associated cyclic neutropenia) when intrinsic response is inadequate.
- Immunogenicity Risk: Because filgrastim is derived from human DNA, it is not species-specific but can be highly immunogenic in dogs and cats. Patients may develop neutralizing antibodies against both the exogenous drug and their own endogenous G-CSF, leading to profound, prolonged, and potentially fatal neutropenia.
- Clinical Strategy: To minimize antibody formation, it is typically administered as a short "pulse" therapy (3 to 5 days) only during the critical nadir of neutropenia.
- Cost: Treatment is highly expensive, which often limits its use in routine veterinary practice.
Mechanism of action
Filgrastim acts as a hematopoietic growth factor.
- It binds specifically to G-CSF receptors located on the surface of myeloid progenitor cells in the bone marrow.
- Receptor activation triggers intracellular signaling pathways (such as the JAK/STAT pathway) → stimulates the proliferation, differentiation, and activation of progenitor cells exclusively within the neutrophil-granulocyte lineage.
- Clinical Pearl: In addition to increasing the absolute number of circulating mature neutrophils, filgrastim also enhances the functional capacity of these cells, including their phagocytic and bactericidal activities, thereby improving the patient's ability to fight off bacterial infections during periods of severe immunosuppression.
Safety & warnings
Contraindications
- Hypersensitivity to filgrastim
- Patients that have previously developed antibodies to filgrastim with resultant neutropenia
Adverse effects
- Severe neutropenia (due to autoantibody formation against G-CSF)
- Myelofibrosis (theoretical/reported concern)
- Medullary histiocytosis (theoretical/reported concern)
- Injection site irritation
- Bone pain
- Splenomegaly
- Hypotension
Precautions
High Risk of Immunogenicity: The development of neutralizing antibodies can cause severe, prolonged neutropenia. Use should generally be restricted to short pulse therapy (≤ 5 days).
- Pregnancy: FDA Category C. High doses have shown adverse effects in pregnant laboratory animals. Use only when benefits clearly outweigh risks.
- Nursing: Unknown if excreted in milk, but unlikely to pose significant risk to nursing offspring.
- Efficacy vs. Risk: Use is controversial due to cost, antibody potential, and lack of definitive evidence showing reduced mortality compared to aggressive broad-spectrum antibiotic therapy alone.
Drug interactions
Avoid using filgrastim within 24 hours of administering antineoplastic agents that target rapidly proliferating cells, as it may exacerbate toxicity to the newly stimulated myeloid cells.
May potentiate the release of neutrophils during G-CSF therapy.
May potentiate the release of neutrophils during G-CSF therapy.
Concurrent administration may increase the incidence of adverse effects. The stimulatory effects of G-CSF on haemopoietic precursors render them more susceptible to the effects of chemotherapy.
Monitoring
- CBC with platelets, routinely (to monitor neutrophil response and detect potential antibody-induced neutropenia)
Pharmacokinetics
Absorption
Rapidly absorbed after subcutaneous injection.
Distribution
Highest concentrations found in the bone marrow, liver, kidneys, and adrenal glands. It is unknown if it crosses the blood-brain barrier, placenta, or enters maternal milk.
Metabolism
Pathways are still under investigation.
Elimination
Elimination pathways are still under investigation.
Overdose
Limited information is available regarding acute toxicity. Because of the high expense of the drug and its apparent limited acute toxic potential, clinically significant overdoses are considered unlikely. If an overdose occurs, monitor CBC closely and provide supportive care.
Available products
Formulations
- Injection
Human-labeled
- Filgrastim Injection: 300 micrograms/mL preservative free in 1 mL and 1.6 mL single dose vials
- Filgrastim Injection: 300 micrograms/0.5 mL preservative free in 0.5 mL and 0.8 mL prefilled syringes; Neupogen (Amgen)
Regulatory status
Human POM (Prescription Only Medicine) used off-label under the cascade.
Human POM used off-label under the cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in the refrigerator (2-8°C). Do not freeze or shake the vial. Never dilute with saline as a precipitate may form. If necessary, it may be diluted into 5% dextrose for injection. If diluted to concentrations between 5 and 15 micrograms/mL, it is recommended to add albumin to a concentration of 2 mg/mL to reduce adsorption to plastic IV tubing. Do not dilute to a concentration of less than 5 micrograms/mL.
Client information
Your veterinarian has prescribed filgrastim to help your pet's bone marrow produce more white blood cells (specifically neutrophils), which are critical for fighting off severe infections.
- Cost: This medication is a human recombinant product and is very expensive.
- Important Risks: Because this is a human protein, your pet's immune system may recognize it as foreign and create antibodies against it. If this happens, the immune system may destroy both the drug and your pet's own natural white blood cells, leading to a life-threatening drop in immunity.
- Short-term Use: To minimize this risk, filgrastim is usually only given for a very short period (3 to 5 days) to get your pet through the most critical phase of their illness.
- Monitoring: Frequent blood tests will be required to ensure the medication is working and to watch for any adverse immune reactions.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.