Medications
Cobimetinib (Cotellic)
A tablet (Cotellic) taken once a day for 21 days of each 28-day cycle, with vemurafenib, for melanoma that has spread or cannot be removed and carries a BRAF V600 gene change, and alone for histiocytic neoplasms (rare blood-cell growth disorders) in adults; it blocks MEK, a step in the growth-signal chain below BRAF.
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.
| Coverage details | |
|---|---|
| Part B status | No cobimetinib row in the CMS Part B Spending by Drug HCPCS file (RY26, data through 2024) — no J-code basis; coverage path is Part D. |
| 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
Unresectable or metastatic melanoma with a BRAF V600E or V600K mutation, in combination with vemurafenib; and, as a single drug, histiocytic neoplasms (rare blood-cell disorders such as Erdheim-Chester disease) in adults.
What it is for, in depth
About half of melanomas carry a BRAF V600 mutation that locks a growth pathway on. Blocking BRAF alone works briefly before the pathway reroutes; adding the MEK blocker cobimetinib improved survival and delayed resistance in trials, at the cost of more sun sensitivity, fever, and diarrhea. Cobimetinib later gained a solo role in histiocytic neoplasms, rare diseases driven by the same pathway, where it produced high response rates in a small trial.
How it works
Cobimetinib blocks MEK, a relay protein in the MAPK growth pathway that BRAF-mutant cancers depend on. In melanoma it is paired with the BRAF blocker vemurafenib so the pathway is shut at two points, which works better and delays resistance.
How it is taken
Tablets by mouth once a day on days 1-21 of each 28-day cycle (three weeks on, one week off), with or without food.
Common side effects
['Diarrhea', 'Sun sensitivity and rash', 'Nausea and vomiting', 'Fever', 'Tiredness', 'Swelling']
Serious warnings
['New skin cancers and severe sun reactions; skin checks and strict sun protection are required (vemurafenib risks are reviewed in its own label)', 'Serious bleeding', 'Heart muscle weakness (reduced ejection fraction), checked with heart scans', 'Eye problems including retinal fluid and detachment, liver injury, and muscle breakdown (rhabdomyolysis)']
Who should be careful
['People with heart failure or reduced heart function', 'People with eye disease or vision symptoms', 'People with liver impairment, who need dose reduction', 'Anyone who cannot avoid strong sun exposure']
Major interactions
['Strong or moderate CYP3A inhibitors such as itraconazole or erythromycin, which raise cobimetinib levels (avoid or adjust)', 'Strong or moderate CYP3A inducers, which lower levels and can make it fail (avoid)', 'Grapefruit products, which raise levels']
Cost and saving notes
Cobimetinib (Cotellic) is a brand-only specialty cancer drug, usually taken with vemurafenib, which carries its own separate specialty-tier cost. Part D plans require prior authorization documenting the BRAF test (for melanoma) or the histiocytic neoplasm diagnosis. Manufacturer copay cards cannot be used with Medicare; charitable foundations may help. Ask about tier exceptions and check Extra Help if your income is limited. The 2027 Part D out-of-pocket cap is $2,400 for the year, and the Medicare Prescription Payment Plan can spread that cost across the year.
Why it is in its tier
Cobimetinib (Cotellic) 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 $32,649 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
What official patient guides say
Take the tablets by mouth once a day, at around the same time every day, with or without food, for the first 21 days of each 28-day cycle, exactly as directed; do not take more or less of it or take it more often than prescribed. If you vomit after taking a dose, do not take another dose; continue your regular dosing schedule. If you miss a dose, skip the missed dose and continue your regular dosing schedule; do not take a double dose to make up for a missed one. Your doctor may lower your dose or temporarily or permanently stop your treatment depending on how well the medication works and how you feel, so be sure to tell your doctor how you are feeling during treatment. Store the tablets in the container they came in, tightly closed and out of reach of children, at room temperature and away from excess heat and moisture, not in the bathroom. Keep all appointments with your doctor and the laboratory; your doctor will order lab tests to check your body's response during and after therapy, and will check your skin before treatment, every 2 months during your treatment, and for up to 6 months after treatment.
Source: MedlinePlus Drug Information
Part D formulary coverage
| Formulary summary | |
|---|---|
| Most common tier | 5 |
| Plans listing this drug | 5495 |
| Total Part D plans | 5495 |
| Share of plans listing it | 100 |
| Formularies listing it | 286 |
| Tier | Plans |
|---|---|
| Tier 1 | 123 plans |
| Tier 2 | 1 plans |
| Tier 4 | 46 plans |
| Tier 5 | 5325 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 copay | $0 — half of plans charge between $0 and $0 |
| Typical coinsurance | 26.0% of the price |
| Based on | 5237 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 2026-11-07
Similar medications
Other medications in the same FDA pharmacologic class (Kinase Inhibitor):
Read next
Part D spending averages (2024)
| Brand name | Generic name | Total claims 2024 | Total spending 2024 | Total beneficiaries 2024 | Rank by beneficiaries 2024 |
|---|---|---|---|---|---|
| Cotellic | Cobimetinib Fumarate | 1518 | 8.16228e+06 | 250 | 2367 |
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
5,495 plans from 509 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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