Fulphila is an injectable medication used to reduce the risk of infection in cancer patients whose immune systems have been weakened by chemotherapy. Specifically, it helps prevent a dangerous condition called febrile neutropenia, where the body’s white blood cell count drops so low that even a minor infection can become life-threatening. The FDA approved Fulphila in June 2018 as the first biosimilar to Neulasta (pegfilgrastim), a well-established drug that has been used for this purpose since 2002.
How Fulphila Works
Chemotherapy drugs are designed to kill fast-growing cancer cells, but they also destroy healthy cells in the process, including the white blood cells your bone marrow produces to fight infection. When white blood cell counts plummet, your body loses its primary defense against bacteria and viruses. This vulnerable window typically hits 7 to 14 days after a chemotherapy cycle, and it’s when infections are most likely to take hold.
Fulphila belongs to a class of drugs called colony-stimulating factors. It works by binding to specific receptors on blood-forming cells in the bone marrow, signaling them to ramp up production of neutrophils, the white blood cells responsible for fighting bacterial infections. By accelerating this process, Fulphila shortens the period when a patient’s immune system is at its weakest. The “peg” portion of the drug (a molecule called polyethylene glycol attached to the active protein) slows the body’s clearance of the medication, meaning a single injection per chemotherapy cycle is typically enough.
Who Is It Prescribed For
Fulphila is approved for patients with non-myeloid cancers, which includes most solid tumors like breast cancer, lung cancer, and colorectal cancer, as well as certain lymphomas. The key requirement is that the chemotherapy regimen carries a clinically significant risk of febrile neutropenia. Not every chemo protocol suppresses white blood cells enough to warrant Fulphila; oncologists assess the specific drugs being used and the patient’s individual risk factors before prescribing it.
Fulphila is not approved for patients with blood cancers that originate in the bone marrow, such as certain leukemias. It is also not indicated for mobilizing stem cells for transplantation, even though related drugs are sometimes used for that purpose.
Fulphila as a Biosimilar to Neulasta
A biosimilar is not a generic drug in the traditional sense. Because biologic medications are made from living cells rather than simple chemical reactions, creating an exact copy isn’t possible. Instead, biosimilars go through extensive testing to demonstrate they are highly similar to the original product with no meaningful clinical differences. Fulphila met this standard against Neulasta, and the FDA granted its approval based on that demonstrated similarity.
For patients, the practical difference is usually cost. Biosimilars tend to be less expensive than the original biologic, which can matter significantly over multiple chemotherapy cycles. In terms of effectiveness and safety, you can expect Fulphila to perform the same way Neulasta does.
What to Expect With Treatment
Fulphila is given as a single subcutaneous injection (just under the skin) once per chemotherapy cycle. The injection is administered at least 24 hours after chemotherapy ends, not before or during treatment. This timing matters because giving it too close to chemotherapy could cause the newly produced white blood cells to be destroyed by the chemo drugs themselves.
The medication comes in a prefilled syringe that must be stored in the refrigerator between 36°F and 46°F. Before use, it needs to sit at room temperature for about 30 minutes. If a syringe has been left out at room temperature for more than 72 hours, or has been frozen more than once, it should be discarded.
Common Side Effects
Bone pain is the most frequently reported side effect of Fulphila and other pegfilgrastim products. This makes biological sense: the drug is pushing your bone marrow into overdrive to produce white blood cells, and that increased activity can cause aching in the bones, particularly in the legs, hips, and lower back. Pain in the arms and legs is also common. For most patients, over-the-counter pain relievers can help manage this discomfort, and the pain typically resolves within a few days of the injection.
Serious Risks
While uncommon, Fulphila carries several serious warnings. Splenic rupture, including fatal cases, has occurred in patients receiving pegfilgrastim products. The spleen plays a role in blood cell storage and filtration, and the rapid increase in white blood cell production can cause it to enlarge. If you experience sudden pain in your left upper abdomen or left shoulder tip after receiving Fulphila, seek medical attention immediately.
Acute respiratory distress syndrome (ARDS), a severe lung condition that causes rapid breathing difficulty, has also been reported. Symptoms to watch for include fever combined with shortness of breath or difficulty breathing in the days following your injection. Severe allergic reactions are another possibility, though they are rare. Signs include swelling of the face or throat, hives, and difficulty breathing.
Sickle cell crises have occurred in patients with sickle cell disease who received pegfilgrastim products, so patients with this condition should discuss the risks carefully with their oncologist before starting treatment.