Filgrastim

Filgrastim is a recombinant form of granulocyte colony-stimulating factor (G-CSF) that binds to G-CSF receptors on myeloid progenitor cells, stimulating proliferation, differentiation, and survival of neutrophil precursors in the bone marrow, leading to increased release of mature neutrophils into circulation. Clinical indications include: (1) prevention/treatment of chemotherapy-induced febrile neutropenia in cancer patients, (2) reducing duration of neutropenia after bone marrow transplantation, (3) mobilization of peripheral blood hematopoietic stem cells prior to collection for autologous or allogeneic stem cell transplantation, and (4) treatment of severe chronic neutropenia (congenital, cyclic, or idiopathic). Mechanism: G-CSF receptor activation triggers JAK-STAT signaling pathway, promoting granulocyte lineage commitment and accelerating maturation. Common adverse effects include bone pain (due to marrow expansion, often treated with antihistamines/NSAIDs), splenomegaly, and rarely splenic rupture. Long-term use in severe congenital neutropenia carries a small increased risk of myelodysplastic syndrome/acute myeloid leukemia. Filgrastim is contraindicated in patients with known hypersensitivity to E. coli-derived proteins (it is produced via recombinant DNA technology in E. coli). Pegfilgrastim is a pegylated, longer-acting form requiring less frequent dosing. Monitoring includes CBC with differential to track neutrophil recovery. It should not be administered 24 hours before or after cytotoxic chemotherapy due to risk of increased sensitivity of rapidly dividing myeloid cells to chemotherapy.