Ropeginterferon alfa-2b (Besremi)

How Medicare covers it

Part D (forms used at home). Part A during a covered inpatient stay. No Part B clinician-administered form in the CMS Part B spending file.

What it treats

Besremi (ropeginterferon alfa-2b-njft) treats two blood disorders in adults: polycythemia vera, a slow-growing blood cancer in which the bone marrow makes too many red blood cells, and essential thrombocythemia, a disorder in which the bone marrow makes too many platelets.

What it is for, in depth

Besremi is a long-acting interferon made for adults with one of two slow-growing bone marrow disorders. In polycythemia vera, the marrow makes too many red blood cells, which thickens the blood and raises the risk of clots. In essential thrombocythemia, the marrow makes too many platelets, which also raises the risk of clots and bleeding. Besremi is prescribed to bring these counts down and keep them controlled over the long term, and for polycythemia vera it can be used for adults whether or not they have already had other treatment such as hydroxyurea; patients switching from hydroxyurea taper that drug off over about 12 weeks while Besremi is started. Treatment continues as long as it keeps counts stable and side effects stay manageable, with blood counts checked regularly. It comes only as an injection under the skin - a 500 mcg/mL prefilled syringe or a 500 mcg/0.5 mL prefilled pen - given every 2 weeks, and possibly every 4 weeks after a year of stable counts in polycythemia vera.

How it works

Besremi is a long-acting interferon alfa-2b. It attaches to interferon alfa receptors on cells in the bone marrow and turns on signals inside those cells that slow down the making of blood cells. This helps bring high red blood cell and platelet counts back down toward normal.

How it is taken

Besremi is injected under the skin (subcutaneous injection) of the lower stomach or the top of the thighs, usually by the patient or a caregiver after training. It comes as a single-dose prefilled syringe (500 mcg/mL) and a single-dose prefilled pen injector (500 mcg/0.5 mL). For polycythemia vera, the starting dose is 100 mcg every 2 weeks (50 mcg if the patient is also taking hydroxyurea), raised by 50 mcg every 2 weeks up to a maximum of 500 mcg until blood counts are stable; after at least 1 year of stability on a steady dose, injections may be spaced to every 4 weeks. For essential thrombocythemia, the dose starts at 250 mcg, rises to 350 mcg at 2 weeks, and then to a maintenance dose of 500 mcg every 2 weeks. Blood counts are checked every 2 weeks while the dose is being raised and every 3 to 6 months after that.

Common side effects

In polycythemia vera, the most common side effects (more than 40% of patients in the label's summary) were flu-like illness, joint pain (arthralgia), fatigue, itching (pruritus), nose and throat inflammation (nasopharyngitis), and muscle and bone pain. Other common effects in polycythemia vera studies included liver enzyme increases, low white blood cell counts, low platelet counts, muscle pain, and flu-like symptoms. In essential thrombocythemia, the most common side effects (more than 20%) were liver enzyme (transaminase) elevations, anemia, fever, increased beta-2 microglobulin in the urine, bacterial infection, itching, and weight loss.

Serious warnings

Besremi can cause or worsen depression and other serious mental health problems, thyroid and other hormone (endocrine) problems including diabetes, heart and blood-vessel problems, low blood counts and bleeding, severe allergic reactions, pancreas inflammation (pancreatitis), colon inflammation (colitis), lung problems, eye problems, high blood fats (lipids), liver injury, kidney injury, tooth and gum problems that can lead to tooth loss, and skin reactions. It can harm an unborn baby, so a pregnancy test is done before starting and effective birth control is required during treatment and for at least 8 weeks after the last dose. Besremi can cause dizziness, sleepiness, or hallucinations, so patients should not drive until they know how it affects them. Treatment is stopped when severe or worsening problems of these kinds do not get better.

Boxed warning

WARNING: RISK OF SERIOUS DISORDERS - Interferon alfa products may cause or worsen fatal or life-threatening disorders of the nerves and mind (neuropsychiatric), the immune system (autoimmune), blood flow (ischemic), and infections. Patients should be watched closely with regular exams and lab tests. Treatment should be stopped in patients whose signs or symptoms of these conditions stay severe or keep getting worse. In many, but not all, cases these disorders go away after the drug is stopped.

Who should be careful

Besremi must not be used by people who have or have had severe psychiatric disorders, especially severe depression, suicidal thoughts, or a suicide attempt; people allergic to interferons or any ingredient in Besremi; people with moderate (Child-Pugh B) or severe (Child-Pugh C) liver impairment; people with a history of or active serious or untreated autoimmune disease; or transplant recipients whose immune system is suppressed. Tell your doctor if you have liver, kidney, heart, thyroid, eye, or mental health problems, or if you are pregnant, plan to become pregnant, or are breastfeeding.

Major interactions

Interferons can raise blood levels of drugs broken down by CYP450 liver enzymes, so patients taking such drugs with a narrow safe range should be watched for side effects and the other drug's dose may need adjusting. Use with other drugs that suppress the bone marrow (myelosuppressive agents) should be avoided because the combination can lower blood counts too much. Use with narcotics (opioids), sleeping drugs (hypnotics), or sedatives should be avoided because of added effects on the brain and nervous system.

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

Ropeginterferon alfa-2b (Besremi) sits on Tier 5 in 96.91% of the plans that list it (5325 of 5495 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 $115,338 per beneficiary for 2024 — among the highest-cost drugs in the program, which matches where plans place it. It is listed by 100.0% of Part D plans. The tier shown is the most common one; individual plans vary.

Sources

• BESREMI (ROPEGINTERFERON ALFA-2B) INJECTION BESREMI PEN (ROPEGINTERFERON ALFA-2B) INJECTION, SOLUTION [PHARMAESSENTIA USA] — DailyMed
• MedlinePlus — National Library of Medicine
• MedlinePlus — Ropeginterferon alfa-2b

What official patient guides say

Besremi (ropeginterferon alfa-2b) comes in a prefilled syringe and is injected under the skin, usually once every 2 weeks; after at least a year, some people move to once every 4 weeks. Your first dose may be given in your doctor's office; after that, you or a helper may inject at home once shown how. Before a shot, take the syringe out of the refrigerator and let it sit 15 to 30 minutes to warm to room temperature — never warm it in a microwave or hot water. Check the liquid: it should be clear and colorless to slightly yellow, with no particles. Inject into the front of your thigh or lower stomach, away from your navel and the 2 inches around it, using a different spot each time; skip irritated, bruised, reddened, infected, or scarred skin. Use a new syringe for every dose, never reuse or share one, and put used syringes in a puncture-resistant container. If you forget a dose, call your doctor, who will tell you when to take it — never inject a double dose. Store the carton in the refrigerator, away from light; do not freeze it, and throw away any syringe that has been frozen.

Source: MedlinePlus — Ropeginterferon alfa-2b

Part D formulary coverage

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

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

Coverage by plan and tier

Of the 5,495 Medicare drug plans we track for 2027, 5,495 list Ropeginterferon alfa-2b (Besremi) — 100% of plans. Most of those plans put it on Tier 5: 5,325 plans, 96.9% of the plans that list it. Other plans place it on Tier 1 (123 plans), Tier 4 (46 plans) or Tier 2 (1 plans). For example: Aetna Medicare Dual Extra (HMO D-SNP) puts it on Tier 5; Aetna Medicare Dual Extra Care (PPO D-SNP) puts it on Tier 5; Aetna Medicare Value Plus (PPO) puts it on Tier 5. You can compare these plans side by side on our Medicare Advantage hub. A tier is not a price. What you pay also depends on whether you have met your plan';s deductible, whether the drug costs a flat copay or a share of the price, and whether you get Extra Help or Medicaid.

Read next

• Part D in 2027: The $700 Deductible, the $2,400 Cap, and the $35 Insulin Rule
• Extra Help in 2027: Lower Drug Copays and Who Qualifies
• Checking Medicare Savings Programs and Extra Help

Part D spending averages (2024)

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

Part D and Medicare Advantage plan sponsors that list this drug on a formulary, 50 at a time.