Filgrastim — Drug Monograph

Brand names: Neupogen, Zarxio (biosimilar), Nivestym (biosimilar), Releuko (biosimilar)

Drug class: Supportive Care Agent

Mechanism of Action

Recombinant human granulocyte colony-stimulating factor (G-CSF) produced in E. coli. Binds the G-CSF receptor (G-CSFR) on myeloid progenitor cells in the bone marrow, activating JAK/STAT, RAS/MAPK, and PI3K/AKT signaling cascades that drive proliferation, differentiation, and survival of neutrophil precursors. Accelerates neutrophil recovery after chemotherapy-induced or radiation-induced myelosuppression. Also mobilizes hematopoietic stem and progenitor cells (HSPCs) from the bone marrow niche into peripheral blood by disrupting the CXCL12–CXCR4 retention axis.

FDA Indications

• Prophylaxis and treatment of chemotherapy-induced neutropenia (CIN) — reduces incidence, severity, and duration of severe neutropenia in patients with non-myeloid malignancies receiving myelosuppressive chemotherapy
• Reduction of infection risk (febrile neutropenia) in patients receiving myeloablative chemotherapy followed by bone marrow transplantation
• Mobilization of hematopoietic progenitor cells (HPCs) for collection by leukapheresis in autologous and allogeneic transplantation
• Severe chronic neutropenia (congenital, cyclic, or idiopathic)
• Hematopoietic subsyndrome of acute radiation syndrome (H-ARS) — increase survival after myelosuppressive radiation exposure ≥2 Gy

Common Side Effects

• Bone pain / medullary bone pain (25–30% — most common; dose-related; due to bone marrow expansion)
• Injection site reactions (SC)
• Nausea
• Headache
• Fatigue
• Fever (transient, post-injection)
• Leukocytosis (expected pharmacodynamic effect; monitor WBC)

Clinical Pearl

The 24-hour rule is the most critical safety consideration: filgrastim must NOT be given within 24 h before or after cytotoxic chemotherapy. Administering G-CSF on the same day as chemotherapy or the day before drives myeloid progenitors into cell cycle, where they are more vulnerable to cytotoxic killing — potentially worsening, not improving, neutropenia. For convenience and adherence, pegfilgrastim (single dose per cycle) is generally preferred over daily filgrastim in most chemotherapy…

Related Therapies & Mechanisms

• Aprepitant (Emend) — Supportive Care Agent
• Avatrombopag (Doptelet) — Supportive Care Agent
• Darbepoetin Alfa (Aranesp) — Supportive Care Agent
• Defibrotide (Defitelio) — Supportive Care Agent