Is it a Part B drug or a Part D drug? The line that decides which appeal applies
Checked against the current rules on September 25, 2026.
Before a Part D denial is really about formulary status or medical necessity, it's worth checking whether the drug belongs under Part D at all — some drugs administered in a doctor's office or infusion center are actually Part B's responsibility.
Source: Medicare Prescription Drug Benefit Manual Ch. 6 — Part D Drugs and Formulary Requirements (Rev. 18, 01-15-16).
The Part D benefit specifically excludes drugs that may be covered under Medicare Part A or Part B for a given individual — the manual's own guidance directs a Part D sponsor to make this determination based on the drug's administration setting and method, not simply its name.Drugs Covered Under Medicare Part A or B
A Part D sponsor has its own due-diligence obligation to correctly determine Part A/B versus Part D coverage before processing a prior authorization or denial — an enrollee shouldn't be left resolving this determination alone.Drugs Covered Under Medicare Part A or B
What this means for your appeal
Records of exactly how, where, and by whom the drug is administered — self-administered at home vs. given by a provider in an office or infusion setting — are the core evidence for this specific category, since the setting and method (not the diagnosis) usually decides which program actually covers it.
This distinction matters because a Part D denial for "not covered under this benefit" sometimes really means "apply under Part B instead" — and the right next step isn't a Part D exceptions request at all, but asking the prescriber's office to bill the drug under Part B, or asking the Part D plan directly which program it believes actually covers the specific administration setting being used.
A drug can also move between the two categories over time for the same patient — a medication that starts as a provider-administered infusion (Part B) and later transitions to a self-administered home version (Part D), or the reverse — so a denial citing this issue is worth double-checking against how the drug is actually being given right now, not how it may have been given previously.
It also matters which entity is actually being appealed to: a Part D plan's own coverage-determination process is the wrong venue for a dispute that's really about Part B coverage, since a standalone Part D plan has no authority to decide a Part B coverage question — that appeal instead runs through the Medicare fee-for-service claims process or, for a Medicare Advantage enrollee, through that plan's own organization determination.
Sources — last checked September 25, 2026
- Drugs Covered Under Medicare Part A or Bas of September 25, 2026
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By CaseWhy Appeals editorial. See how this content is produced. Not legal advice. Not affiliated with or endorsed by Medicare, CMS, or any health plan. A product of CaseWhy LLC.
