Fulphila is a prescription medication used to help prevent infections in people undergoing certain types of chemotherapy. It is a biosimilar to Neulasta (pegfilgrastim), one of the most widely used supportive drugs in cancer care. The FDA approved Fulphila in June 2018, making it the first biosimilar to Neulasta available in the United States. It is manufactured by Mylan GmbH.
What Fulphila Does
Chemotherapy attacks fast-growing cells, which includes cancer cells but also the white blood cells your body relies on to fight infection. When white blood cell counts drop dangerously low, a condition called neutropenia, even a mild infection can become life-threatening. A fever during neutropenia (febrile neutropenia) is a medical emergency that often leads to hospitalization.
Fulphila works by stimulating your bone marrow to produce more white blood cells, specifically a type called neutrophils. It’s classified as a leukocyte growth factor. By boosting neutrophil production after each chemotherapy cycle, Fulphila helps close the window of vulnerability when your immune system is at its weakest. It is specifically approved for patients with non-blood cancers (non-myeloid malignancies) who are receiving chemotherapy drugs known to cause a significant drop in white blood cells.
What “Biosimilar” Means for You
A biosimilar is not a generic drug in the traditional sense. Biologics like Neulasta are made from living cells, so an exact copy isn’t possible the way it is with a simple chemical pill. Instead, a biosimilar must demonstrate that it is highly similar to the original product with no meaningful differences in safety, effectiveness, or quality. The FDA requires extensive testing to confirm this.
Fulphila went through multiple clinical studies to earn its approval. In a key trial involving breast cancer patients receiving chemotherapy, Fulphila proved equivalent to Neulasta in reducing the duration of severe neutropenia. Additional studies in healthy volunteers confirmed that the two drugs behave the same way in the body, producing similar immune responses and similar patterns of antibody development. The practical takeaway: Fulphila works like Neulasta at a potentially lower cost.
How It’s Given
Fulphila is administered as a single injection under the skin (subcutaneous injection), typically in the upper arm, abdomen, or thigh. You receive one dose per chemotherapy cycle. The timing matters: it should not be given in the 14 days before chemotherapy or within 24 hours after chemotherapy, because stimulating white blood cell production too close to a chemo dose can make cells more vulnerable to the treatment’s effects.
The injection is usually given at your oncology clinic, though some patients learn to self-inject at home. If you store it yourself, keep it refrigerated between 36°F and 46°F. It can stay at room temperature for up to 72 hours, but anything beyond that or any syringe that has been frozen more than once should be discarded.
Common Side Effects
The most frequently reported side effect is bone pain, which occurs in roughly 31% of patients compared to 26% of those receiving a placebo. This makes sense given how the drug works: it’s pushing your bone marrow into overdrive to produce white blood cells, and that increased activity can cause aching in the bones, particularly in the hips, spine, and legs. Pain in the arms or legs is also more common, affecting about 9% of patients versus 4% on placebo.
For most people, bone pain is manageable with over-the-counter pain relievers and tends to ease within a few days of the injection. If the pain is severe or doesn’t improve, your care team can adjust your approach.
Serious but Rare Risks
Like the original Neulasta, Fulphila carries warnings about several uncommon but serious complications. Splenic rupture has been reported in rare cases, both in cancer patients and healthy donors receiving similar drugs. Symptoms to watch for include sudden pain in the left upper abdomen or left shoulder tip. Acute respiratory distress syndrome (a severe form of lung inflammation) is another rare risk, typically showing up as sudden shortness of breath or worsening breathing after starting treatment.
People with sickle cell disease face an additional concern, as drugs in this class have been associated with sickle cell crises. Allergic reactions, including serious ones, are also possible, particularly in people who have had prior reactions to pegfilgrastim products. Kidney inflammation (glomerulonephritis) has been reported as well, though this remains uncommon.
Who Should Not Use Fulphila
Fulphila is not appropriate for everyone on chemotherapy. It is specifically not indicated for mobilizing stem cells for transplantation purposes. People with a history of serious allergic reactions to pegfilgrastim or any component of the formulation should avoid it. Your oncologist will determine whether Fulphila is right for your specific treatment plan based on the type of chemotherapy you’re receiving and your overall risk of developing febrile neutropenia.