In this article, we will discuss Filgrastim (Mechanism of Action). So, let’s get started.

Mechanism of Action

Colony-stimulating factors are glycoproteins which act on hematopoietic cells by binding to specific cell surface receptors and stimulating proliferation‚ differentiation commitment‚ and some end-cell functional activation. Endogenous G-CSF is a lineage-specific colony-stimulating factor that is produced by monocytes‚ fibroblasts, and endothelial cells. G-CSF regulates the production of neutrophils within the bone marrow and affects neutrophil progenitor proliferation‚ differentiation, and selected end-cell functions (including enhanced phagocytic ability‚ priming of the cellular metabolism associated with respiratory burst‚ antibody-dependent killing, and the increased expression of some cell surface antigens). G-CSF is not species-specific and has been shown to have minimal direct in vivo or in vitro effects on the production or activity of hematopoietic cell types other than the neutrophil lineage.


In phase 1 studies involving 96 patients with various nonmyeloid malignancies‚ filgrastim administration resulted in a dose-dependent increase in circulating neutrophil counts over the dose range of 1 to 70 mcg/kg/day.

This increase in neutrophil counts was observed whether filgrastim was administered intravenous (1 to 70 mcg/kg twice daily)‚ subcutaneous (1 to 3 mcg/kg once daily)‚ or by continuous subcutaneous infusion (3 to 11 mcg/kg/day). With discontinuation of filgrastim therapy‚ neutrophil counts returned to baseline in most cases within 4 days. Isolated neutrophils displayed normal phagocytic (measured by zymosan-stimulated chemoluminescence) and chemotactic (measured by migration under agarose using N-formyl-methionyl-leucyl-phenylalanine [fMLP] as the chemotaxin) activity in vitro.
The absolute monocyte count was reported to increase in a dose-dependent manner in most patients receiving filgrastim; however‚ the percentage of monocytes in the differential count remained within the normal range.

Absolute counts of both eosinophils and basophils did not change and were within the normal range following administration of filgrastim. Increases in lymphocyte counts following filgrastim administration have been reported in some normal subjects and patients with cancer. White blood cell (WBC) differentials obtained during clinical trials have demonstrated a shift towards earlier granulocyte progenitor cells (left shift‚ including the appearance of promyelocytes and myeloblasts‚ usually during neutrophil recovery following the chemotherapy-induced nadir. In addition‚ Dohle bodies‚ increased granulocyte granulation‚ and hypersegmented neutrophils have been observed. Such changes were transient and were not associated with clinical sequelae, nor were they necessarily associated with infection.

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