What is an NDC number?
Each listed drug product listed is assigned a unique 10-digit, 3-segment number. This number, known as the NDC, identifies the labeler, product, and trade package size. The first segment, the labeler code, is assigned by the FDA. A labeler is any firm that manufactures (including repackers or relabelers), or distributes (under its own name) the drug. The second segment, the product code, identifies a specific strength, dosage form, and formulation for a particular firm. The third segment, the package code, identifies package sizes and types. Both the product and package codes are assigned by the firm. The NDC will be in one of the following configurations: 4-4-2, 5-3-2, or 5-4-1.
An asterisk may appear in either a product code or a package code. It simply acts as a place holder and indicates the configuration of the NDC. Since the NDC is limited to 10 digits, a firm with a 5 digit labeler code must choose between a 3 digit product code and 2 digit package code, or a 4 digit product code and 1 digit package code.
Thus, you have either a 5-4-1 or a 5-3-2 configuration for the three segments of the NDC. Because of a conflict with the HIPAA standard of an 11 digit NDC, many programs will pad the product code or package code segments of the NDC with a leading zero instead of the asterisk
Since a zero can be a valid digit in the NDC, this can lead to confusion when trying to reconstitute the NDC back to its FDA standard. Example: 12345-0678-09 (11 digits) could be 12345-678-09 or 12345-0678-9 depending on the firm’s configuration. By storing the segments as character data and using the * as place holders we eliminate the confusion. In the example, FDA stores the segments as 12345-*678-09 for a 5-3-2 configuration or 12345-0678-*9 for a 5-4-1 configuration.
As published by the FDA in the National Drug Code Directory http://www.fda.gov/drugs/informationondrugs/ucm142438.htm