Anatomy Of An FDA SNI

Important Notice To Readers of This Essay On November 27, 2013, President Barack Obama signed the Drug Quality and Security Act of 2013 into law. That act has many provisions, but one is to pre-empt all existing and future state serialization and pedigree laws like those that previously existed in California and Florida. Some or all of the information contained in this essay is about some aspect of one or more of those state laws and so that information is now obsolete. It is left here only for historical purposes for those wishing to understand those old laws and the industry’s response to them.The U.S. Food and Drug Administration (FDA) published their “Standardized Numerical Identification (SNI) for Prescription Drug Packages – Final Guidance” document almost two years ago (see my essay “FDA Aligns with GS1 SGTIN For SNDC” from back then).  The guidance was published as purely non-binding recommendations that reflected the Agency’s current thinking, but in my opinion it is a nice piece of work and can be used as a practical guide, as far as it goes, for implementing drug serialization programs today.

Why is that?  It’s because drug manufacturers and repackagers need to serialize all of their prescription drugs that enter the state of California in 2015/2016.  Can those companies make use of the FDA’s SNI guidance to comply with the serialization requirements of the California Pedigree Law?  I will answer that question in this essay, but first


According to the FDA, an “SNI” is a unique identifier that is attached to a prescription drug by the original manufacturer.  Presumably “unique” means unique within the United States.  Specifically, an SNI is either a “serialized National Drug Code (sNDC)” or one of the existing recognized standards for identifying and labeling certain blood and blood components and certain minimally manipulated human cells, tissues and cellular and tissue-based products (HCT/Ps) which do not currently use NDC numbers.  The guidance document mentions only ISBT 128 for this latter class of SNI and implies that there may be others.  Apparently those standards always result in a unique identification number for each product package.  The important thing to realize is that an the sNDC is only one type of SNI but it is the kind that should be used on any prescription drug product that has been assigned an NDC.  In this essay I am only going to discuss the sNDC type of SNI.

The FDA defines the sNDC as being composed of the drug’s 10-digit NDC plus an alphanumeric serial number that can be up to 20 characters long.  The guidance applies to prescription drugs only so Over-The-Counter (OTC) drugs that are identified by an NDC apparently aren’t covered.  But since the guidance is non-binding anyway this distinction isn’t really significant.  Perhaps it will if the SNI guidance ever becomes a required regulation.

Example of the components of an sNDC borrowed from the FDA SNI Guidance document. March 2010. Click image to enlarge.

The SNI guidance document itself defines the SNI “for package-level identification only”, but it also makes it clear that SNIs can also exist for levels other than the package-level, like cases and pallets.  It’s just that this guidance document doesn’t cover those.  The FDA defines the “package-level” this way:

“…the smallest unit placed into interstate commerce by the manufacturer or the repackager that is intended by that manufacturer or repackager, as applicable, for individual sale to the pharmacy or other dispenser of the drug product.”

Repackagers that break the manufacturer’s package down and repackages the contents in any way must apply a new and unique SNI to the new package-level and that new SNI must be linked (in some unspecified way that I assume is a database) back to the manufacturer’s original SNI.  The guidance document contains an excellent example of a package of six drug-filled syringes that would be the lowest packaging level that the hypothetical manufacturer intended pharmacies or other dispensers to buy, but is then repackaged by another hypothetical party acting as a repackager into single syringe packages for sale to pharmacies or other dispensers.

The original hypothetical manufacturer would only need to assign an SNI to the package of six drug-filled syringes since it does not intend the syringes for individual sale.  However, the hypothetical repackager would need to assign each drug-filled syringe its own unique SNI and link those six SNI’s to the original manufacturer’s SNI that was assigned to the specific package of six that the individual packages came from.  If you repackage drugs you should study the example in the FDA SNI guidance document.  Of course, since this guidance is not binding the FDA isn’t saying that you have to do this today.

The FDA recommends that the SNI should generally “…be applied to each package in both human-readable and machine-readable forms.”  However, the FDA guidance document explicitly states that “…at this time, FDA is not specifying the means of incorporating the SNI onto the package.”  But it goes on to say that “The SNIs described in this guidance are compatible with, and flexible for, encoding into a variety of machine-readable forms of data carriers, such as 2-dimensional bar codes and radio-frequency identification (RFID)…”.  The document also explicitly doesn’t specify a location on the package where the SNI should be placed, but it does say that any human-readable form could be printed “…in a non-contiguous manner…” from the existing NDC printed on the package.


Finally, the guidance document points out that the sNDC “…is compatible with, and may be presented within, a [GS1] GTIN…”.  GTIN is a GS1 standard for general product/service class-level identification and the letters stand for “Global Trade Item Number” (see my essays “Anatomy of a GTIN” and “Depicting An NDC Within a GTIN”).  It is quite clear that what the FDA meant to say is that the sNDC can be depicted as a serialized GS1 GTIN, or “sGTIN”.  It does not say that an sGTIN is the only way to depict an sNDC or that you must depict it that way, it simply says that it may be presented that way.

The document doesn’t identify any other way to do it but I’m pretty confident you could present an sNDC using HIBCC standards too if you wanted to.  HIBCC product identification standards are very rare in the U.S. pharmaceutical supply chain (they are much more common in the medical devices supply chain) so I’m not covering them in this essay.  For more on HIBCC standards click here.


This question is frequently asked these days.  Fortunately the answer is definitively “yes” in my opinion.  You should read the source documents to convince yourself one way or the other, but here is my logic.  [UPDATE:  In fact, in 2012 the California Board of Pharmacy adopted a regulation that explicitly makes the FDA SNI the “official” unique identifier for drugs.  See “California Enforcement Subcommittee Moves To Require FDA SNI“.  –Dirk]

The text of the California pedigree law says that each drug package distributed within the state must have a “unique identification number” attached to it.  Presumable “unique” here means unique within the state of California.  The law doesn’t specify any specific characteristics of the identifier itself other than its uniqueness and that it be “…contained within a standardized nonproprietary data format and architecture, that is uniformly used by manufacturers, wholesalers, and pharmacies…“.  The FDA sNDC is a “unique identification number” and by definition it must be unique, presumably within the U.S., and it is a standardized nonproprietary data format and architecture and it is certainly capable of being uniformly used by all parties in the U.S. pharma supply chain, which fulfills the California requirement.

The language in the California law and the Questions and Answers about the law that was published by the California Board of Pharmacy in 2008 regarding who must apply a unique identifier, to what and when it must be done is comparable to the language in the FDA’s SNI guidance.  This includes the definition of the “package-level” and the need for a unique identifier attached to repackaged drugs and how that identifier must be linked to the original manufacturers unique identifier.  Of course, the language in the California documents was available to the FDA when they were constructing their language.

So far I haven’t found a single significant difference in characteristics of the unique identifier defined by California and the sNDC defined by the FDA.  This leads me to conclude that California will very likely accept the use of unique identifiers that conform to the FDA sNDC guidance for compliance with the serialization requirements of their pedigree law.  It also makes perfect sense that they would.  Again, that’s my opinion.  You form your own.


OK, so you agree with me and you want to print an FDA-compliant sNDC on your drug packages within a machine-readable barcode using GS1 standards in advance of the compliance dates for the California pedigree law.  The way to do it is to make use of “The GS1 System”.  Here I’m referring to the GS1 Application Identifier standard and certain barcode symbologies that are documented fully in the GS1 General Specification. Search for this specification on the internet or contact your local GS1 Member Organization (MO) to obtain a copy.

The GS1 System Application Identifier standard defines a way of encoding multiple pieces of information within a string of characters in an exact way so that a reader can extract them back into their original decomposed form.  There are lots of Application Identifiers (AI) covering a wide spectrum of data types needed in a supply chain context.  An AI is a two-to-four-digit code that identifies the type of data that follows it in an “element string”.  In our particular instance, we are interested in just two AIs: one for the GTIN (AI=”01”) and one for the serial number that is associated with that GTIN (AI=”21”).

A GTIN element string is always 14 digits long when it is depicted using AI “01”.  Remember that the FDA defined their serial number as being up to 20 alphanumeric characters.  That means that it is a variable length value ranging from 1 to 20 characters.  It is a happy coincidence that GS1 defines their serial number element string for AI “21” in exactly the same way!  Well, in fact, the FDA made the decision to specifically align their definition with that of GS1’s existing AI “21” definition so that there wouldn’t be any conflict if people chose to use GS1 standards to implement the sNDC.

If we put together the technique I described in my essay “Depicting An NDC Within a GTIN” with the information above, we get the following shortcut for the GS1 string of elements that depict an sNDC:

sNDC to GS1 string of elements shortcut. Click image to enlarge.

Now all we need to do is encode this string of characters into one of the GS1 barcode symbologies that accommodate a GS1 string of elements.  These include GS1-128 and DataBar for linear barcodes and GS1 DataMatrix for 2D barcodes.  See the GS1 General Specification for details on how to properly construct these barcodes.

(NOTE:  According to the HDMA only a subset of the possible DataBar family of symbologies should be used on pharmaceuticals in the U.S. supply chain and they should only be used on products that are very tiny.  See my recent essay “Updated HDMA Barcode Guidance: A Must Read”.)

To construct the human readable string for an sNDC that is encoded in a GS1 string of elements you may insert spaces between the end of the GTIN and the “21” and you may set off the AIs by wrapping them in parentheses.  These “decorations” are commonly used to help make these long numbers more readable and they should never be included in the string that is encoded in the barcode.

Here is an example GS1 string of elements that uses the same data that the FDA included for an example sNDC in their guidance document (shown in the image above).  In their example they used a fictitious NDC of 55555 666 77 and a serial number of 11111111111111111111.  Applying the shortcut technique I show above the GS1 string of elements would be:

sNDC example from the FDA Guidance document encoded into a GS1 string of elements. Click image to enlarge.

The string that would be used to encode the GS1 barcode would be:


and the human readable to be printed on the drug package might look like this:

(01) 003 55555 666 77 6 (21) 11111111111111111111

Notice the extra decorations I included in the human readable that are not included in the string that is encoded in the barcode.


In a departure from the GS1 General Specification, GS1’s RFID tag standards do not make use of AI’s when encoding an sGTIN for product identification.  In fact, in their RFID standards the concept of a GTIN and a serial number are merged together to produce a single indivisible  identifier they explicitly call a Serialized Global Trade Item Number, or SGTIN (see the GS1 Tag Data Standard for the details).

A full explanation of how to encode an SGTIN within a GS1 RFID tag is more complex than the barcode explanation above and it is beyond the scope of this essay (and of RxTrace, really) but you will find the GS1 Tag Data Standard document (now in revision 1.6) to be quite well written (see my essay “Masterpiece:  GS1 Tag Data Standard 1.5”).  And don’t miss my widely read essay “RFID Is DEAD…At Unit Level In Pharma”.


There are some surprising implications that result from the definition of a serial number in the way the FDA defines the sNDC.  I hope to cover those implications in a future essay.  Stay tuned.


2-13-2012:  Corrected a problem with the GS1 string of elements and the human readable example.  Thanks to George Wright IV of PIPS for reporting the problem.

2 thoughts on “Anatomy Of An FDA SNI”

  1. I can not seem to find the regulations specific to 2d barcoding in your essay.

    What I need to know is if there is a reqirement to have a 2d matrix barcode per say?

    Also if this is,is there any guidance for companies that would like to update their packs ahead of the 2015 requirement?

    1. Nicola,
      Thanks for your comment. That’s right. You won’t find the regulation that requires 2D barcoding in my essay because there isn’t one. You will find links to the current California Pedigree Regulations that require serialization without specifying a data carrier. You will also find links to the current FDA SNI guidance that describes non-binding recommendations for constructing a serialized NDC (sNDC), but it stops short of including a specific data carrier, although it hints at GS1 data carriers. I recommend that you read my last four essays that have dealt with various aspects of the U.S. state and federal regulations and non-binding “thinking” on serialization and the technology available to fulfill them. Make sure you read the pertinent source material that I have linked to. You may still not know what to do, but you will be in good company because that’s the problem that everyone is facing right at this time. Stay tuned to,,, PMP News and other sources for breaking developments and to and for analysis this year and in future years. Everyone expects actions to occur, but no one knows exactly what those actions will be until they happen. Thanks for reading.


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