Filgrastim
Filgrastim is recombinant human granulocyte colony-stimulating factor used selectively to support neutrophil recovery in animals. It can stimulate canine and feline marrow despite its human origin. Veterinary applications concern selected severe neutropenias with responsive marrow precursors; evidence for improved clinical outcomes varies with the cause of marrow suppression.
Group
Granulocyte colony-stimulating factor
Mechanism of Action
Filgrastim binds granulocyte colony-stimulating factor receptors on hematopoietic precursor cells. Receptor signaling promotes proliferation, differentiation and release of cells in the neutrophil lineage and can enhance mature neutrophil function. The resulting rise in circulating neutrophils depends on available responsive marrow cells and the nature of the underlying marrow injury.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Neutrophil recovery | 5 mcg/kg | SC | Every 24 h | Up to 5 days; Limited veterinary evidence; discontinue earlier when counts recover. Use as a short pulse, normally no more than 5 days, to reduce neutralizing-antibody risk; follow CBC. |
| Alternative neutrophil recovery regimen | 10 mcg/kg | SC | Every 24 h | Up to 5 days; Alternative listed daily regimen; duration and stop point depend on CBC response. Use as a short pulse, normally no more than 5 days, to reduce neutralizing-antibody risk; follow CBC. |
| Neutrophil recovery | 1–5 mcg/kg | SC | Every 24 h | Up to 5 days; Short pulse; stop according to neutrophil recovery. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Neutrophil recovery | 5 mcg/kg | SC | Every 24 h | Up to 5 days; Limited veterinary evidence; discontinue earlier when counts recover. Use as a short pulse, normally no more than 5 days, to reduce neutralizing-antibody risk; follow CBC. |
| Alternative neutrophil recovery regimen | 10 mcg/kg | SC | Every 24 h | Up to 5 days; Alternative listed daily regimen; duration and stop point depend on CBC response. Use as a short pulse, normally no more than 5 days, to reduce neutralizing-antibody risk; follow CBC. |
| Neutrophil recovery | 1–5 mcg/kg | SC | Every 24 h | Up to 5 days; Short pulse; stop according to neutrophil recovery. |
| Acute severe neutropenia | 5 mcg/kg | SC | Every 12 h | Up to 5 days; Alternative short-pulse regimen; efficacy and antibody risk must be assessed. |
Indications
- Selected severe neutropenia after chemotherapy or other reversible marrow suppression in dogs and cats, with condition-specific evidence.
- Adjunctive stimulation of neutrophil recovery in selected infectious or drug-associated neutropenias, with limited evidence of a survival benefit.
Contraindications
- Serious hypersensitivity to filgrastim
- Use in animals intended for food
- Prior filgrastim-associated neutralizing antibodies with neutropenia
Interactions
- Avoid administration within 24 hours of cytotoxic chemotherapy targeting rapidly dividing cells unless an oncology-specific protocol establishes timing.
Adverse effects
- Injection-site pain
- Potential hypersensitivity
- Possible antibody-mediated loss of response with prolonged heterologous protein use
- Neutralizing-antibody-associated prolonged neutropenia
- Potential abnormal marrow tissue responses with prolonged exposure
Toxicity
Stop treatment for serious hypersensitivity or excessive leukocyte response and provide appropriate care.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Neupogen vial 300 mcg/mL Amgen Single-dose vial. Refrigerate 2–8°C and protect from light; do not shake or dilute with saline. | Injection | 300 mcg / mL | SC, IV |
| Neupogen prefilled syringe 300 mcg/0.5 mL Amgen SC-only prefilled syringe, 300 mcg per 0.5 mL; do not interchange its volume with the 300 mcg/mL vial. | Injection | 300 mcg / 0.5 mL | SC |
Monitoring and Administration
Monitor CBC and absolute neutrophil count; stop when neutrophil recovery is adequate.
Avoid shaking; protect from light and keep Neupogen refrigerated at 2–8°C. Its SC product is not reconstituted like sargramostim.
Neupogen must not be diluted with saline. IV dilution, if specifically needed, uses dextrose with product-specific adsorption precautions.
Human-origin G-CSF may induce antibodies against both administered and endogenous G-CSF, causing severe prolonged neutropenia. Avoid reuse after this reaction. Longer courses, including a previously described two-week course, have been reported, but short pulses of at most 5 days are generally preferred.
For a listed feline response-guided course, treatment stops when neutrophils exceed 3,000/mcL for 2 days; interpret this alongside the short-pulse limit.
If an IV dilution is specifically prescribed, 5% dextrose may be used. At 5–15 mcg/mL, human albumin 2 mg/mL is described to limit adsorption; do not dilute below 5 mcg/mL. Saline can precipitate filgrastim.