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

SEPTEMBER 01, 2008
Michael J. Gaunt, PharmD

Dr. Gaunt is a medication safety analyst and the editor of ISMP Medication Safety Alert! Community/Ambulatory Care Edition.

The National Drug Code (NDC) is a system used to identify unique drug products. An NDC number for a specific product is created by the the FDA and the manufacturer to ensure that products can be differentiated; no currently marketed products are to have the same NDC number. Published by FDA, an NDC number contains 10 digits organized into 3 distinct segments: the labeler code, the product code, and the package code, in that order. Most pharmacists recognize 11-digit NDC numbers using a 5-digit labeler code, a 4-digit product code, and a 2-digit package code as the NDC format (eg, 12345-6789-01), as this is the format typically used in computer systems and printed on pharmacy-generated labels.

The FDA assigns a unique labeler code to the manufacturer. Thus, all products from a given manufacturer will begin with the same labeler code. The manufacturer then assigns a product code, which is unique among its products, to represent the drug and dosage strength, as well as a package code for the package size.

Unfortunately, the number of digits that comprise segments within an NDC number may vary. For example, some labeler codes are 5 digits, whereas others are 4 digits, and some product codes contain only 3 digits. This can make it confusing for practitioners and software programs to decode an NDC number, because the lack of a standard code format may make it difficult to distinguish the different portions of the NDC number. To force standardization, many vendors and drug information content providers insert a leading zero at the beginning of the labeler code, product code, or package code to create 11-digit numbers.


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The Institute for Safe Medication Practices has received a number of reports of different manufacturers using identical or very similar product codes for different products. Although the 11-digit numbers are unique, duplication of the product code—the middle 4 digits—is causing product mix-ups in pharmacies. A patient requested a refill of the antiarrhythmic quinidine gluconate 324 mg (NDC 00677-0675-01). When preparing the prescription, however, the pharmacy technician selected quinine sulfate 325 mg (NDC 13279-0675-10), an antimalarial, from the shelf, as the 2 products were side-by-side. The pharmacist verified the technician's work by confirming the middle 4 digits of the NDC, which matched. The patient recognized that the pills were different when she looked at her prescription at the pharmacy counter; this allowed the error to be corrected before the patient left the store.

In another case, a patient returned to the community pharmacy with a question about the change in color and shape of the medication he had received. The patient was supposed to receive propranolol long-acting capsules (Inderal LA) 60 mg (NDC 00046-0470-81) for management of his hypertension, but he received immediate-release propranolol 60 mg (NDC 50111-0470-01). Again, the pharmacist who filled the prescription had checked the middle 4 digits of the NDC number during final verification, but the prescribed product and the erroneously dispensed product had identical product codes.

Safe Practice Recommendations

Consider the following measures to reduce the likelihood of mix-ups between products that have identical or very similar product codes:

  • Ensure the complete NDC number is used when manually verifying product selection. This should be done by comparing the NDC number on the manufacturer's product label with the NDC number printed on the pharmacy-generated label.
  • Incorporate a review of NDC numbers into failure mode and effects analysis processes when evaluating new products for addition to store/ warehouse stock and insurer formularies to identify potential mix-ups.
  • Manufacturers should assign distinctly different NDC numbers to products. Overlapping product codes should be avoided.
  • The FDA should improve premarket screening of NDC numbers to minimize this risks associated with duplicate product codes.