When to Give Filgrastim
Filgrastim should be initiated 24-72 hours (1-3 days) after completing myelosuppressive chemotherapy and continued daily until the absolute neutrophil count (ANC) recovers to 2,000-3,000/mm³. 1, 2
Primary Prophylaxis Indications
Start filgrastim prophylactically when the chemotherapy regimen carries >20% risk of febrile neutropenia. 3 This is the most critical decision point for preventing life-threatening complications.
Dosing and Administration
- Dose: 5 mcg/kg/day subcutaneously 1, 2
- Timing: Begin 24-72 hours after the last dose of chemotherapy 1, 2
- Duration: Continue until ANC reaches 2,000-3,000/mm³ (do NOT target >10,000/mm³) 2, 3
- Route: Subcutaneous injection is preferred 1
Critical Timing Considerations
Real-world evidence shows that same-day administration (within 24 hours of chemotherapy) may be appropriate in select patients when logistical barriers prevent optimal timing, though it is less effective than the recommended 24-72 hour window. 1, 4 However, administration >72 hours after chemotherapy significantly worsens outcomes including higher rates of severe neutropenia. 4
Therapeutic Use in Established Febrile Neutropenia
Consider filgrastim 5 mcg/kg/day in patients with febrile neutropenia who have high-risk features, though it will not reduce mortality. 3 While filgrastim consistently shortens neutropenia duration by approximately 1-2 days and reduces hospitalization, it does not improve survival. 5, 6
High-Risk Features Warranting Treatment
- Severe neutropenia (ANC <100/mm³) 5
- Anticipated prolonged neutropenia (>7-10 days expected)
- Sepsis syndrome or multiorgan dysfunction
- Pneumonia or invasive fungal infection
- Age >65 years 3
Absolute Contraindications
Never administer filgrastim in these situations:
- During concurrent chest/thoracic radiotherapy - increases complications and mortality 1, 2
- Within 24 hours before or simultaneously with chemotherapy - significantly increases risk of severe thrombocytopenia and febrile neutropenia 2, 3
- In patients without neutropenia, especially those with community- or hospital-acquired pneumonia 1, 3
Special Clinical Situations
Post-Transplant Setting
- Autologous stem cell transplant: Start filgrastim 24-120 hours after high-dose therapy 1
- Allogeneic transplant: May safely delay initiation until day 5-7 post-transplant 2
- Continue until ANC >1,000/mm³ for 3 consecutive days 1
Pediatric Acute Leukemia
Avoid routine use in pediatric AML/ALL due to theoretical concerns about stimulating leukemic blast growth and increased risk of therapy-related myeloid leukemia or myelodysplastic syndrome, especially with concurrent radiation, topoisomerase II inhibitors, or alkylating agents. 1, 2, 3
Stem Cell Mobilization
- Dose: 10 mcg/kg/day (higher than prophylaxis dose) 1
- Timing: Start at least 4 days before first leukapheresis 1
- Duration: Continue through last leukapheresis procedure 1
Alternative: Pegfilgrastim
Pegfilgrastim 6 mg as a single dose is equally effective to 10-11 days of daily filgrastim and may be preferred for convenience. 1, 7
Pegfilgrastim Specifics
- Timing: Administer once, 24 hours after chemotherapy completion (ideally 1-3 days post-chemotherapy) 1
- Same-day administration: Less effective than delayed administration but acceptable when logistical barriers exist 1
- Weight restriction: Do not use 6 mg formulation in patients <45 kg 1
- Not indicated for: Stem cell mobilization 1
Common Pitfalls to Avoid
- Starting too late: Administration >72 hours post-chemotherapy significantly increases neutropenia complications 4
- Continuing too long: Stop when ANC reaches 2,000-3,000/mm³; targeting >10,000/mm³ is unnecessary and wasteful 2, 3
- Using in low-risk regimens: Do not use prophylactically when febrile neutropenia risk is <20% 3
- Inadequate duration in first cycle: The first chemotherapy cycle has the highest neutropenia rates; ensure full course administration 8
- Administering with radiotherapy: Absolute contraindication for concurrent chest radiation 1, 2