Interferon beta-1a (Avonex)

How Medicare covers it

Part D (self-injected at home in the usual case). Part B can apply to the intramuscular form when it is given by a clinician (HCPCS Q3027 in the CMS Part B spending file — see the Part B basis in this package). Part A during a covered inpatient stay.

What it treats

Relapsing forms of multiple sclerosis (MS) in adults, including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.

What it is for, in depth

Avonex is for adults with relapsing forms of multiple sclerosis: clinically isolated syndrome (a first MS-like attack), relapsing-remitting MS, and active secondary progressive MS. It is a long-term disease-modifying treatment — it is taken every week on an ongoing basis to reduce relapses and slow the disease, not to treat a relapse that is happening now. In the treatment path it is one of the older first-line platform therapies for relapsing MS: many patients start on an interferon or a similar platform drug, and move to stronger therapies if relapses or MRI activity continue. It comes in one strength — 30 micrograms in a 0.5 mL single-dose prefilled syringe or a prefilled auto-injector pen (the two forms in this package) — with a starter titration kit that begins at quarter doses. The separate subcutaneous interferon beta-1a product (Rebif, different strengths) is a different dashboard product and is not part of this package.

How it works

Interferon beta-1a is a manufactured copy of natural human interferon beta, a protein the immune system makes. It binds to receptors on cell surfaces and switches on interferon-response genes; the exact way this calms MS relapses is not known (the label states the mechanism in MS is unknown).

How it is taken

Injection into the muscle (intramuscular) only, 30 micrograms once a week, from a single-dose prefilled syringe or the Avonex Pen auto-injector. Treatment may start low (7.5 micrograms) and rise by 7.5 micrograms a week over 3 weeks to lessen flu-like symptoms; the first injection is given under a health professional's supervision. Pain relievers or fever reducers on treatment days may help with flu-like symptoms.

Common side effects

The most common reactions (at least 5% more often than placebo) were flu-like symptoms — chills, fever, muscle aches, and weakness — usually lasting about a day after the injection and lessening over time. Headache, injection-site pain and inflammation, nausea, joint pain, and urinary tract infection were also more common than with placebo.

Serious warnings

Depression, suicidal thinking, and psychosis have been reported — new mood symptoms should be reported right away. Severe liver injury, including liver failure, has been reported rarely, so liver tests are monitored. Injection-site reactions can include tissue death (necrosis), abscess, and cellulitis. Other labeled risks: anaphylaxis and other allergic reactions, worsening of heart failure, lowered blood counts, seizures, thrombotic microangiopathy (a serious blood-vessel and kidney condition), pulmonary arterial hypertension, and new autoimmune disorders.

Who should be careful

Do not use if you have had an allergic reaction to natural or recombinant interferon beta. Use with monitoring in people with depression or other psychiatric illness, liver disease, heart failure, low blood counts, or seizure disorders. Safety in children has not been established.

Major interactions

The Avonex label carries no drug-interaction section and reports no formal interaction studies; the label does advise care with other drugs that can injure the liver (hepatotoxic drugs, and alcohol) because liver injury risk may add up.

Cost and saving notes

This is a Tier 5 specialty drug in most plans: Medicare's 2027 Part D out-of-pocket cap ($2,400 for the year) and Extra Help (the Part D low-income subsidy) are the main Medicare cost routes, and a tier exception or formulary exception can be requested when a plan does not list it.

Why it is in its tier

Interferon beta-1a (Avonex) sits on Tier 5 — the specialty tier — in 89.4% of the plans that list it (928 of 1,038 listing plans). Tier 5 is the highest 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 are clear: Avonex is a brand-only biologic with no generic, and the CMS dashboard puts its average Part D spending at about $79,472 per beneficiary for 2024 — among the highest-cost drugs in the program, exactly the cost level plans reserve for the specialty tier. Only 18.89% of Part D plans list Avonex at all, so many readers will find their plan does not list it and covers a different MS drug instead. The tier shown is the most common one; individual plans vary.

Sources

• AVONEX (interferon beta-1a) kit / injection, solution — DailyMed
• MedlinePlus — Interferon Beta-1a Intramuscular Injection

What official patient guides say

This package is for Avonex, the form of interferon beta-1a injected into a muscle. MedlinePlus has a separate page for the under-the-skin (Rebif) form, which is not the form in this package and is not used here. The intramuscular form comes as a liquid in prefilled syringes and in a prefilled automatic injection pen, and it is injected into a muscle usually once a week, on the same day each week, at about the same time of day. Your doctor may start you on a low dose and raise it slowly, no more than once a week. It controls the symptoms of MS but does not cure it, so keep using it even if you feel well, and do not stop without talking to your doctor. A doctor or nurse will show you or a caregiver how to prepare and inject it at home, and you should read the patient information that comes with it before your first use. Use a new prefilled syringe and needle, or a new pen, for every injection and never reuse them; throw used ones away in a hard, puncture-proof container kept out of reach of children. Before you inject, check that the liquid is clear and colorless — do not use it if it is cloudy, discolored, has particles, or is past its date. With a prefilled syringe you can inject into your upper arms or thighs; with the pen, into the outer surface of your upper thighs. Use a different spot each time, do not use the same spot two times in a row, and do not inject where the skin is sore, red, bruised, scarred, infected, or irritated. Two hours after injecting, check the spot for redness, swelling, or tenderness, and call your doctor if a skin reaction does not go away in a few days. If you forget a dose, inject it as soon as you remember it, but do not inject two days in a row and do not inject a double dose; go back to your regular schedule the following week, and call your doctor if you miss a dose and have questions. Store the prefilled syringes and pens in the refrigerator, out of reach of children — do not freeze them and do not expose them to high heat. If no refrigerator is available, they can be kept at room temperature, away from heat and light, for up to 7 days.

Source: MedlinePlus — Interferon Beta-1a Intramuscular Injection

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

Without insurance, the cash benchmark is 8777.77714 per unit (AVONEX 30 MCG/0.5 ML SYRINGE KIT (4 PACK)) — about nan for 30 units. NADAC benchmark — the average price pharmacies pay (CMS, as of 2026-11-04). Pharmacy shelf prices vary.

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, 1,038 list Interferon beta-1a (Avonex) — 18.9% of plans. Most of those plans put it on Tier 5: 928 plans, 89.4% of the plans that list it. Other plans place it on Tier 1 (100 plans), Tier 4 (9 plans) or Tier 2 (1 plans). For example: CareSource MyCare Ohio (HMO D-SNP) puts it on Tier 1; Essence Advantage Select (HMO) puts it on Tier 5; UPMC for Life PPO Rx Enhanced (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.