How to read a master file letter of authorization

A sponsor referencing someone else’s Drug Master File doesn’t get to read it. The confidential manufacturing details stay with FDA and the file’s holder; what the referencing applicant gets is a Letter of Authorization, and the letter is only as useful as what it specifically says it covers.

What the Master File itself is for

A Drug Master File lets a manufacturer of an API, excipient, packaging component, or other input submit detailed, confidential information about their facility or process directly to FDA — once, instead of disclosing it to every company that wants to buy from them and repeating that disclosure in every application those customers file. Type II covers drug substances and intermediates, Type III covers packaging materials, Type IV covers excipients, colorants, flavors, and similar materials, and Type V covers FDA-accepted reference information that doesn’t fit the other categories — Type I, which once covered manufacturing-site information, was eliminated in 2000. None of it gets reviewed in isolation: FDA’s own description of the process is that the agency ordinarily neither independently reviews a DMF nor approves or disapproves it, and instead reviews the content only when an application under part 314 or part 312 — including an IND — points to it.

What the Letter of Authorization actually permits

The LOA is the DMF holder’s written statement giving FDA permission to look at specified parts of the file in support of a named applicant’s submission, under 21 CFR 314.420. A usable letter identifies the DMF number, the holder, the specific person or company authorized to reference it, and — the part worth reading closely — exactly what information in the file that authorization covers. It can be limited to certain sections, certain grades of material, or a single application rather than every submission the applicant might ever file. The referencing applicant cites the DMF number and the LOA in their own submission; FDA matches the two and reviews the underlying file without disclosing its contents to the applicant. Holding an LOA doesn’t entitle the applicant to read the file themselves — that’s the entire point of the arrangement, and a CMC section built on an assumed scope of authorization is a strategy problem that surfaces as an operations problem later, usually close to a filing deadline.

Why the scope — and the currency — of the letter matters

An LOA isn’t a one-time formality. The DMF holder commits to keeping the file current and to notifying FDA and the authorized party in writing of additions, changes, or deletions. A letter written for one application doesn’t automatically extend to a later supplement or a different product line unless its own language covers that. Practically, before relying on a referenced DMF: confirm the LOA on file actually names your application, not just your company; confirm it covers what you need from the file rather than a narrower slice than assumed; and confirm with the DMF holder directly that the underlying file is current, since the applicant has no independent way to check its contents. That last step is a smaller, more procedural instance of the same discipline behind reading what a document actually authorizes instead of what its existence seems to imply.

The Letter of Authorization is a small document doing a specific, limited job: connecting an applicant’s submission to someone else’s confidential file without disclosing that file’s contents. Reading it for what it actually authorizes — not what its existence seems to promise — is what keeps a CMC section from resting on an assumption nobody checked.