When should filgrastim (Granulocyte-Colony Stimulating Factor (G-CSF)) be administered after chemotherapy?

When to Give Filgrastim After Chemotherapy

Filgrastim should be started 24 to 72 hours (1 to 3 days) after completion of myelosuppressive chemotherapy and continued daily until the absolute neutrophil count (ANC) recovers to 2,000-3,000/mm³. 1

Timing of Administration

Standard Chemotherapy Regimens

• Start filgrastim 24-72 hours after the last dose of chemotherapy at a dose of 5 mcg/kg/day subcutaneously 1
• Never administer filgrastim on the same day as chemotherapy - this is not recommended due to potential interference with chemotherapy efficacy and increased risk of adverse events 1, 2
• Continue daily injections until post-nadir ANC recovery to normal or near-normal levels (ANC ≥2,000-3,000/mm³) 1

High-Dose Therapy and Stem Cell Transplant

• For autologous stem cell rescue, filgrastim can be started 1 to 5 days after high-dose chemotherapy 1
• Post-transplant: begin on day +5 after stem cell infusion and continue until ANC recovery (>1,500/mm³ for 2 days) 1

Critical Timing Considerations

Why the 24-72 Hour Window Matters

The delay between chemotherapy completion and filgrastim initiation is essential because:

• Administering G-CSF concurrently with chemotherapy may increase myelosuppression by expanding the pool of rapidly dividing myeloid progenitor cells that are vulnerable to cytotoxic agents 3
• Evidence shows same-day pegfilgrastim (the long-acting form) results in longer duration of severe neutropenia and increased risk of febrile neutropenia compared to next-day administration 1

Duration of Therapy

• Continue filgrastim through all cycles of chemotherapy - prophylaxis limited to only the first 2 cycles results in significantly higher rates of febrile neutropenia (36% vs 10%) compared to prophylaxis through all 6 cycles 1
• Do not stop prematurely; continue until ANC reaches 2,000-3,000/mm³ after the nadir 1

Special Clinical Situations

Concurrent Chemoradiation

• Do not use prophylactic filgrastim with concurrent chemotherapy and radiation therapy, particularly when the mediastinum is in the radiation field 1, 3
• This combination significantly increases risk of thrombocytopenia and pulmonary toxicity 3

Acute Myeloid Leukemia (AML)

• Start filgrastim 24 hours after completion of induction or consolidation chemotherapy 1
• Continue until ANC ≥1,000/mm³ for 3 consecutive days or ≥10,000/mm³ for 1 day, maximum 35 days 2, 4
• This reduces median duration of severe neutropenia from 19 to 14 days 2

Dosing Specifics

Standard Dose

• 5 mcg/kg/day subcutaneously for prophylaxis after myelosuppressive chemotherapy 1
• Round to the nearest vial size based on institution-defined weight limits 1

Stem Cell Mobilization

• Higher dose of 10 mcg/kg/day may be preferable for peripheral blood progenitor cell mobilization 1
• Start 4 days before first leukapheresis and continue until last leukapheresis 1

Common Pitfalls to Avoid

Do Not:

• Administer within 14 days before chemotherapy or within 24 hours after chemotherapy per FDA labeling 2, though guidelines support the 24-72 hour window 1
• Use with concurrent chemoradiation involving the mediastinum 3
• Stop prophylaxis after only 1-2 cycles when multiple cycles are planned 1
• Administer on the same day as chemotherapy except in rare circumstances where it's the only feasible option 1

Monitor For:

• Bone pain, arthralgias, and myalgias (common side effects) 3
• ANC levels to determine when to discontinue therapy 1
• Signs of febrile neutropenia despite prophylaxis 2

Alternative: Pegfilgrastim

If using pegfilgrastim (long-acting G-CSF) instead of daily filgrastim:

• Single 6 mg dose administered 24-72 hours after chemotherapy 1
• Effective for chemotherapy cycles given every 3 weeks (Category 1 evidence) 1
• Same-day pegfilgrastim is less effective but acceptable if patient cannot return for next-day dosing 1