Medications
Pegfilgrastim-pbbk (Fylnetra)
A self-injected biosimilar of pegfilgrastim (a Neulasta biosimilar, Fylnetra) — a long-acting white-blood-cell growth factor given once per chemotherapy cycle to lower the chance of infection from a low neutrophil count (febrile neutropenia).
How Medicare covers it
Part D (self-injected syringes used at home where a plan lists them). Part B covers the clinician-given injection where the CMS Part B spending file carries it (HCPCS Q5130 — see the Part B basis in this package). Part A during a covered inpatient stay.
| Coverage details | |
|---|---|
| Part B status | CMS Part B Spending by Drug HCPCS file (RY26, data through 2024) carries Q5130 (injection, pegfilgrastim-pbbk (fylnetra), biosimilar, 0.5 mg): the clinician-given biosimilar path has a Part B basis; the self-injected home form is the Part D aggregation in this package. |
| Medicare Advantage | Most Medicare Advantage plans that include drug coverage (MAPD plans) use the same formulary-and-tier system; the plan's own drug list decides coverage and copay — check the plan's formulary. |
| Medicare Supplement (Medigap) | Medicare Supplement (Medigap) plans sold today do not include prescription drug coverage; drug coverage comes from Part D or an MAPD plan. |
What it treats
Fylnetra (pegfilgrastim-pbbk) lowers the chance of infection, shown as febrile neutropenia (fever with a low white blood cell count), in people with cancers other than myeloid cancers who are getting chemotherapy drugs that lower white blood cells. It is also used to increase survival in people who were suddenly exposed to high doses of radiation that damage the bone marrow (hematopoietic subsyndrome of acute radiation syndrome).
What it is for, in depth
Fylnetra is a biosimilar of Neulasta (pegfilgrastim), a long-acting white blood cell growth factor. It is prescribed for people with cancers other than myeloid cancers whose chemotherapy lowers neutrophils enough to raise the risk of fever and infection (febrile neutropenia). It fits into the treatment path as support care given once in each chemotherapy cycle, at least 24 hours after chemotherapy, so the bone marrow recovers faster between cycles. It is also approved to increase survival after sudden exposure to bone-marrow-damaging doses of radiation, given as two doses one week apart. Fylnetra comes only as a 6 mg/0.6 mL single-dose prefilled syringe for injection under the skin, with smaller weight-based doses for children under 45 kg drawn differently under medical direction.
How it works
Fylnetra is a biosimilar to Neulasta (pegfilgrastim). It is a leukocyte (white blood cell) growth factor: it binds to receptors on blood-forming cells in the bone marrow and tells the body to make more neutrophils, the white blood cells that fight infection. Making more neutrophils shortens the time the count stays dangerously low after chemotherapy.
How it is taken
Fylnetra is given as an injection under the skin (subcutaneous) from a single-dose prefilled syringe (6 mg in 0.6 mL). For chemotherapy patients, the usual dose is one 6 mg injection once per chemotherapy cycle, and it must not be given in the 14 days before or in the 24 hours after chemotherapy. Children who weigh less than 45 kg get a lower dose based on weight. For sudden radiation exposure, the dose is two 6 mg injections given one week apart, starting as soon as possible after exposure.
Common side effects
The most common side effects (at least 5% more often than with placebo) are bone pain and pain in an arm or leg.
Serious warnings
Fylnetra can cause serious problems, including a ruptured spleen (which can be fatal — get help at once for pain in the left upper belly or left shoulder), a serious lung problem called acute respiratory distress syndrome (ARDS), serious allergic reactions including anaphylaxis, sickle cell crises in people with sickle cell disorders, kidney inflammation (glomerulonephritis), very high white blood cell counts, low platelets, capillary leak syndrome (fluid leaking from blood vessels), inflammation of the aorta (aortitis), and, with long-term use in some patients, myelodysplastic syndrome and acute myeloid leukemia. It is not used to mobilize stem cells for a stem cell transplant.
Who should be careful
Do not use Fylnetra if you have had a serious allergic reaction to pegfilgrastim products or filgrastim products. Tell your doctor if you have sickle cell disease, kidney problems, or latex sensitivity is not an issue here because the needle cap is not made with natural rubber latex. Tell your doctor if you are pregnant or breastfeeding — the label has limited data in pregnancy.
Major interactions
The Fylnetra label does not list specific drug interactions and does not name drugs that must be avoided with it. The main timing rule is about chemotherapy itself: Fylnetra must not be given between 14 days before and 24 hours after cytotoxic chemotherapy. Tell your care team about all medicines you take.
Cost and saving notes
If this drug is covered under your Medicare Part D plan and the cost is high, you can ask your plan for a tier exception to pay a lower cost share. If you have limited income, Extra Help (the Part D Low-Income Subsidy) can lower your Part D premiums and drug costs. In 2027, your total yearly out-of-pocket spending on covered Part D drugs is capped at $2,400, and you can spread those costs out in monthly payments through the Medicare Prescription Payment Plan.
Why it is in its tier
Pegfilgrastim-pbbk (Fylnetra) sits on Tier 5 in 97.78% of the plans that list it (88 of 90 listing plans). Tier 5 is the specialty tier — instead of a flat copay, patients usually pay a percentage of the drug's cost (coinsurance), which is why specialty drugs feel expensive even with coverage. The data-visible drivers: It is a brand-only product with no generic version in the formulary data, and the CMS dashboard puts its average Part D spending at about $8,245 per beneficiary for 2024 — a high-cost drug, which matches where plans place it. Only 1.64% of Part D plans list it at all, so many readers will find their plan does not list it and covers a similar drug instead. The tier shown is the most common one; individual plans vary.
Sources
- FYLNETRA (PEGFILGRASTIM) INJECTION [AMNEAL PHARMACEUTICALS LLC] — DailyMed
- MedlinePlus — National Library of Medicine
- MedlinePlus — Pegfilgrastim Injection
What official patient guides say
Pegfilgrastim-pbbk (Fylnetra) is an injection under the skin, not a pill, so you can keep your normal diet. Your doctor sets the exact timing around your chemotherapy — for chemo patients the label dose is a single shot once per chemotherapy cycle, given with a single-dose prefilled syringe. A nurse may give the shot, or you may be trained to give it yourself at home. Do not shake the syringe, and always check the liquid before you inject: do not use it if it looks cloudy or discolored, has particles in it, or is past its expiration date. Use each syringe only once, even if liquid is left in it, and put used needles and syringes in a puncture-resistant container. MedlinePlus gives no catch-up rule — if you miss a scheduled home dose, ask your doctor what to do instead of doubling up. Store Fylnetra in the refrigerator in its carton, away from direct sunlight, and do not freeze it; it may sit at room temperature for up to 72 hours. Bone pain and pain in the arms or legs are common.
Part D formulary coverage
| Formulary summary | |
|---|---|
| Most common tier | 5 |
| Plans listing this drug | 90 |
| Total Part D plans | 5495 |
| Share of plans listing it | 1.64 |
| Formularies listing it | 17 |
| Tier | Plans |
|---|---|
| Tier 1 | 1 plans |
| Tier 2 | 1 plans |
| Tier 5 | 88 plans |
Source: CMS Prescription Drug Plan Formulary, Pharmacy Network, and Pricing Information Files — Monthly file 2026-10-15 (plan year 2027), file 2027_20261008.zip (data.cms.gov dataset ed1496ea-23e7-41f1-9292-172fa842ccfb): basic drugs formulary file + plan information file, both dated 20261031 inside the zip; downloaded and aggregated 2026-10-30. Medication RxCUI sets resolved through the NLM RxNav (RxNorm) API.
What you pay
| With Medicare Part D | |
|---|---|
| Most common tier | Tier 5 |
| Typical coinsurance | 28.0% of the price |
| Based on | 87 plans that cover this drug · 2027 plan year |
A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.
Sources: CMS Plan Benefit Package + formulary data; CMS NADAC · Checked 2026-11-08
Similar medications
Other medications in the same FDA pharmacologic class (Leukocyte Growth Factor):
Read next
Part D spending averages (2024)
| Brand name | Generic name | Total claims 2024 | Total spending 2024 | Total beneficiaries 2024 | Rank by beneficiaries 2024 |
|---|---|---|---|---|---|
| Fylnetra | PEGfilgrastim-Pbbk | 175 | 511181 | 62 | 2884 |
Source: CMS Medicare Part D Spending by Drug (Drug Spending Dashboard), release RY26 P04 V10, data through 2024 (DSD_PTD_RY26_P04_V10_DY24_BGM.csv), downloaded 2026-10-30
Companies covering this drug
90 plans from 22 companies list this drug on a formulary for 2027. Search by company or plan name, or filter by tier. Cost sharing is the plan's published amount for this drug's tier in the initial coverage stage (1-month retail supply), where the plan publishes it; a blank means the plan does not publish it.
| Company | Plan | Tier | Copay | Coinsurance |
|---|
A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.
Coverage and costs change. Drug lists (formularies), tiers, and copays can change during the year and differ by plan. Always check with your insurance company or plan directly to confirm what is covered and what you will pay.
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