Filgrastim is a recombinant human granulocyte colony-stimulating factor (G-CSF) produced by recombinant DNA technology in E. coli. It is a 175-amino acid protein with a molecular weight of approximately 18.8 kDa. It differs from endogenous human G-CSF by the addition of an N-terminal methionine and is non-glycosylated. In the Indian context, it is a critical supportive care biologic used primarily to stimulate neutrophil production and reduce the incidence of febrile neutropenia in patients undergoing myelosuppressive chemotherapy.
Adult: **Chemotherapy-induced neutropenia:** 5 mcg/kg (approx. 300 mcg for a 60 kg adult) subcutaneously or IV daily. Start at least 24 hours after chemotherapy. Continue until neutrophil recovery (ANC reaches 10,000/mm3 after nadir). **Mobilization:** 10 mcg/kg/day subcutaneously. **Chronic Neutropenia:** Starting dose 5 mcg/kg/day subcutaneously, adjust based on ANC.
Note: For subcutaneous use: Inject into upper arm, abdomen (except 2-inch area around navel), thigh, or upper outer area of buttock. Rotate injection sites. Do not inject into areas that are tender, red, bruised, hard, or have scars or stretch marks. The 300 mcg prefilled syringe is for single use only. Allow to reach room temperature for 30 minutes before injection. Do not shake. Inspect for particulate matter or discoloration before use.
Filgrastim binds specifically to G-CSF receptors on the surface of committed myeloid progenitor cells and mature neutrophils. This binding activates intracellular signaling pathways (primarily JAK/STAT, MAPK, and PI3K), leading to proliferation, differentiation, and functional activation of neutrophil lineage cells. It promotes the release of mature neutrophils from the bone marrow into the bloodstream and enhances neutrophil survival.
Pregnancy: Category C (US FDA). Animal studies have shown adverse effects. There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus. Indian guidelines recommend use only when clearly needed.
Driving: Filgrastim may cause fatigue, dizziness, or headache. Patients should be cautioned about driving or operating machinery if they experience these effects.
| Lithium | May potentiate the release of neutrophils; concurrent use may result in increased neutrophil counts. Monitor WBC. | Moderate |
| Chemotherapeutic Agents (e.g., Cyclophosphamide, Doxorubicin) | Filgrastim should NOT be administered in the 24-hour period before through 24 hours after chemotherapy due to potential for increased sensitivity of rapidly dividing myeloid cells to chemotoxicity. | High |
| Other Myeloid Growth Factors (e.g., Sargramostim) | Concurrent use is not recommended due to lack of clinical benefit and potential for additive adverse effects. | Moderate |