1. Clinical Overview
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.
| Onset | Duration | Bioavailability |
|---|---|---|
| Neutrophil counts begin to rise within 24 hours, with a significant increase typically observed within 3-5 days of administration. | The pharmacodynamic effect (elevated neutrophil count) persists for approximately 24-48 hours after a single dose, necessitating daily administration during the chemotherapy nadir period. | Approximately 60-70% following subcutaneous injection. |
2. Mechanism of Action
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.
3. Indications & Uses
- To decrease the incidence of infection, as manifested by febrile neutropenia, in patients with non-myeloid malignancies receiving myelosuppressive anti-cancer drugs associated with a significant incidence of severe neutropenia with fever.
- For reducing the time to neutrophil recovery and the duration of fever following induction or consolidation chemotherapy in patients with Acute Myeloid Leukemia (AML).
- To reduce the duration of neutropenia and neutropenia-related clinical sequelae (e.g., febrile neutropenia) in patients with non-myeloid malignancies undergoing myeloablative chemotherapy followed by bone marrow transplantation.
- For chronic administration to reduce the incidence and duration of sequelae of neutropenia (e.g., fever, infections, oropharyngeal ulcers) in symptomatic patients with congenital, cyclic, or idiopathic neutropenia.
- For mobilization of hematopoietic progenitor cells into the peripheral blood for collection by leukapheresis.
4. Dosage & Administration
Adult Dosage: **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.
Administration: 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.
5. Side Effects
Common side effects may include:
- Bone pain (mild to moderate, in lower back, pelvis, sternum)
- Musculoskeletal pain
- Headache
- Injection site reactions (redness, swelling, pain)
- Fatigue
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| 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 |
7. Patient Counselling
- DO store the prefilled syringe in the refrigerator (2-8°C) in its original carton. Do not freeze.
- DO allow the syringe to reach room temperature for about 30 minutes before injecting. Do not warm it in any other way.
- DO inspect the solution. It should be clear and colorless. Do not use if cloudy, discolored, or contains particles.
- DO NOT shake the syringe.
- DO use a different injection site each day. Rotate sites.
- DO NOT inject Filgrastim within 24 hours before or after your chemotherapy dose.
- DO dispose of the used syringe in a puncture-proof sharps container. Do not throw in household trash.
8. Toxicology & Storage
Overdose: Symptoms are extensions of pharmacologic effects: pronounced leukocytosis (WBC > 100,000/μL), severe bone pain, splenomegaly, dyspnea, and potential for ARDS or capillary leak syndrome. Thrombocytopenia may occur.
Storage: Store at 2°C to 8°C (in a refrigerator). Do not freeze. Keep the prefilled syringe in the original carton to protect from light. Do not shake. If needed, the syringe may be kept at room temperature (not above 25°C) for a single period of up to 15 days, after which it should not be returned to the refrigerator and must be discarded if not used. Protect from direct heat and light. Keep out of reach of children.