NDCs: The Same "Middle 4" Does Not Mean Equal

Pharmacy Times, Volume 0, 0

Verifying prescriptions by checking the National Drug Code's 4-digit product identifier is not enough; duplication of these "middle 4" numbers can cause product mix-ups in pharmacies.

Dr. Gaunt is a medication safetyanalyst and the editor of ISMPMedication Safety Alert!Community/Ambulatory CareEdition.

The National Drug Code (NDC) isa system used to identify uniquedrug products. An NDC numberfor a specific product is created by thethe FDA and the manufacturer to ensurethat products can be differentiated; nocurrently marketed products are to havethe same NDC number. Published byFDA, an NDC number contains 10 digitsorganized into 3 distinct segments: thelabeler code, the product code, andthe package code, in that order. Mostpharmacists recognize 11-digit NDCnumbers using a 5-digit labeler code,a 4-digit product code, and a 2-digitpackage code as the NDC format (eg,12345-6789-01), as this is the formattypically used in computer systems andprinted on pharmacy-generated labels.

The FDA assigns a unique labeler codeto the manufacturer. Thus, all productsfrom a given manufacturer will beginwith the same labeler code. The manufacturerthen assigns a product code,which is unique among its products, torepresent the drug and dosage strength,as well as a package code for the packagesize.

Unfortunately, the number of digitsthat comprise segments within an NDCnumber may vary. For example, somelabeler codes are 5 digits, whereas othersare 4 digits, and some product codescontain only 3 digits. This can make itconfusing for practitioners and softwareprograms to decode an NDC number,because the lack of a standard codeformat may make it difficult to distinguishthe different portions of the NDCnumber. To force standardization, manyvendors and drug information contentproviders insert a leading zero at thebeginning of the labeler code, productcode, or package code to create 11-digitnumbers.

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The Institute for Safe MedicationPractices has received a number ofreports of different manufacturers usingidentical or very similar product codes fordifferent products. Although the 11-digitnumbers are unique, duplication of theproduct code—the middle 4 digits—iscausing product mix-ups in pharmacies.A patient requested a refill of the antiarrhythmicquinidine gluconate324 mg(NDC 00677-0675-01). When preparingthe prescription, however, the pharmacytechnician selected quinine sulfate 325mg (NDC 13279-0675-10), an antimalarial,from the shelf, as the 2 productswere side-by-side. The pharmacist verifiedthe technician's work by confirmingthe middle 4 digits of the NDC, whichmatched. The patient recognized thatthe pills were different when she lookedat her prescription at the pharmacycounter; this allowed the error to be correctedbefore the patient left the store.

In another case, a patient returned tothe community pharmacy with a questionabout the change in color and shapeof the medication he had received. Thepatient was supposed to receive propranolollong-acting capsules (InderalLA) 60 mg (NDC 00046-0470-81) formanagement of his hypertension, but hereceived immediate-release propranolol60 mg (NDC 50111-0470-01). Again, thepharmacist who filled the prescriptionhad checked the middle 4 digits of theNDC number during final verification, butthe prescribed product and the erroneouslydispensed product had identicalproduct codes.

Safe Practice Recommendations

Consider the following measures toreduce the likelihood of mix-ups betweenproducts that have identical or very similarproduct codes:

  • Ensure the complete NDC number isused when manually verifying productselection. This should be done bycomparing the NDC number on themanufacturer's product label withthe NDC number printed on thepharmacy-generated label.
  • Incorporate a review of NDC numbersinto failure mode and effectsanalysis processes when evaluatingnew products for addition to store/warehouse stock and insurer formulariesto identify potential mix-ups.
  • Manufacturers should assign distinctlydifferent NDC numbers toproducts. Overlapping product codesshould be avoided.
  • The FDA should improve premarketscreening of NDC numbers tominimize this risks associated withduplicate product codes.