1. Clinical Overview
Filgrastim is a recombinant human granulocyte colony-stimulating factor (G-CSF) analog produced by recombinant DNA technology in E. coli. It is a 175-amino acid protein with an N-terminal methionine. It stimulates the proliferation, differentiation, and functional activation of neutrophils, thereby reducing the duration and severity of neutropenia. In the Indian context, it is a critical supportive care agent in oncology and hematology.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 24 hours, with a significant rise in absolute neutrophil count (ANC) typically observed within 1-2 days. | The effect on neutrophil counts is transient; counts begin to decline within 24-48 hours after discontinuation, returning to baseline within 1-7 days. | Approximately 60-70% after subcutaneous injection. |
2. Mechanism of Action
Filgrastim binds to specific cell surface receptors (G-CSFR) on hematopoietic progenitor cells and mature neutrophils. This binding activates intracellular signaling pathways (primarily JAK/STAT, MAPK, and PI3K), leading to the proliferation and differentiation of neutrophil precursors in the bone marrow, release of mature neutrophils from the marrow into the bloodstream, and enhancement of neutrophil survival and function (including phagocytosis, superoxide production, and antibody-dependent cellular cytotoxicity).
3. Indications & Uses
- Prophylaxis of febrile neutropenia in patients receiving myelosuppressive chemotherapy (e.g., for solid tumors, non-myeloid malignancies).
- Reduction in the duration of neutropenia and neutropenic complications in patients undergoing myeloablative chemotherapy followed by bone marrow transplantation.
- Mobilization of autologous hematopoietic progenitor cells (stem cells) into the peripheral blood for collection by leukapheresis.
4. Dosage & Administration
Adult Dosage: **Chemotherapy-induced neutropenia:** 5 mcg/kg/day (approx. 150-300 mcg for a 60kg adult) SC/IV, starting at least 24 hours after chemotherapy, continued until ANC reaches 10,000/mm³ post-nadir. **Stem cell mobilization:** 10 mcg/kg/day SC, for 4-7 days. **Chronic neutropenia:** Starting dose 5 mcg/kg/day SC, adjusted based on response.
Administration: For subcutaneous injection: Administer in the abdomen, thigh, or upper arm. Rotate injection sites. The 150mcg vial/pre-filled syringe is for single use only. Do not shake. Inspect for particulate matter or discoloration before use. Can be administered by a healthcare professional or a trained patient/caregiver.
5. Side Effects
Common side effects may include:
- Bone pain (mild to moderate, often in lower back, pelvis, sternum).
- Injection site reactions (erythema, pain, swelling).
- Headache.
- Fatigue.
- Nausea.
- Fever.
- Elevated lactate dehydrogenase (LDH), alkaline phosphatase, uric acid.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Lithium | May potentiate the release of neutrophils; monitor for excessive leukocytosis. | Moderate |
| Chemotherapeutic Agents (e.g., Cyclophosphamide, Doxorubicin) | Filgrastim should NOT be administered 24 hours before to 24 hours after chemotherapy due to potential for increased toxicity to rapidly dividing myeloid cells. | High |
| Corticosteroids | May enhance the myeloid proliferative effect; clinical significance unknown. | Low |
| Other Myelosuppressive Drugs (e.g., Ganciclovir, Zidovudine) | May counteract the neutrophil-stimulating effect of Filgrastim. | Moderate |
7. Patient Counselling
- DO administer the injection at the same time each day as prescribed.
- DO rotate injection sites to prevent skin reactions.
- DO store the medication in the refrigerator (2°C to 8°C). Do not freeze.
- DO NOT shake the vial or pre-filled syringe.
- DO NOT use the medication if it is cloudy, discolored, or contains particles.
- DO NOT administer Filgrastim in the 24-hour period before or after your chemotherapy dose.
8. Toxicology & Storage
Overdose: Symptoms are extensions of pharmacological effects: excessive leukocytosis (WBC >100,000/mm³), bone pain, splenomegaly, potential for splenic rupture, dyspnea, and ARDS. Thrombocytopenia may occur due to marrow 'crowding'.
Storage: Store in a refrigerator at 2°C to 8°C in the original carton to protect from light. Do not freeze. Avoid shaking. If needed, the pre-filled syringe (in its carton) may be kept at room temperature (not above 30°C) for a single period of up to 72 hours. Once removed from the refrigerator and warmed to room temperature, do not return to the fridge. Discard any unused portion. Keep out of reach of children.