Filgrastim binds to the G-CSF receptor and stimulates the production of neutrophils in the bone marrow. As a G-CSF analog, it controls proliferation of committed progenitor cells and influences their maturation into mature neutrophils. Filgrastim also stimulates the release of neutrophils from bone marrow storage pools and reduces their maturation time. Filgrastim acts to increase the phagocytic activity of mature neutrophils. In patients receiving cytotoxic chemotherapy, Filgrastim can accelerate neutrophil recovery, leading to a reduction in duration of the neutropenic phase

Used in the treatment of chemotherapy-induced neutropenia by enhancing the production of neutrophils. Filgrastim acts on hematopoietic cells by binding to specific cell surface receptors thereby stimulating proliferation, differentiation, commitment, and end cell functional activation. When tbo-filgrastim is administered to cancer patients, it took 3-5 days to reach maximum absolute neutrophil count (ANC). Levels of neutrophils returned to baseline by 21 days following completion of chemotherapy. In the healthy volunteer trials, doubling the tbo-filgrastim subcutaneous dose from 5 to 10 mcg/kg resulted in a 16-19% increase in the ANCmax and a 33-36% increase in the area under the effect curve for ANC.

1. Wang B, Ludden TM, Cheung EN, Schwab GG, Roskos LK: Population pharmacokinetic-pharmacodynamic modeling of filgrastim (r-metHuG-CSF) in healthy volunteers. J Pharmacokinet Pharmacodyn. 2001 Aug;28(4):321-42. Pubmed
2. FDA label for Neupogen and tbo-filgrastim