The NDC system was originally established as an essential part of an out-of-hospital drug reimbursement program under Medicare. The NDC serves as a universal product identifier for human drugs. The current edition of the National Drug Code Directory is limited to prescription drugs and a few selected over-the-counter (OTC) products. The directory consists of prescription and selected OTC insulin, domestic, and foreign drug products that are in commercial distribution in the United States. The products have been listed in accordance with the Drug Listing Act and applicable Code of Federal Regulations for submitting drug product information to the FDA. NDC therapeutic class codes are used to identify each of 20 major drug classes to which the drug entry may belong, adapted from Standard Drug Classifications in the National Drug Code (NDC) Directory, 1995. The two-digit categories are general and represent all subcategories (e.g., Antimicrobial agents), and the specific four-digit categories represent the breakouts of the general category (e.g., Penicillin). The general two-digit codes include medications that do not fit into any of the subcategories (four-digit codes). Starting in 1995, the NDC four-digit classes were changed to include more classes than the previous classification in 1985. Therefore some drugs switched from a general two-digit class into a more specific four-digit class. In addition, drugs may be approved for several different therapeutic classes. Some drugs receive approval for additional therapeutic uses after their initial approval, so the same drug can change classes because of new uses.

Numerous drug products have many uses and/or indications. In an effort to categorize the vast number of the broad ‘‘analgesic’’ or pain-relief individual products in the marketplace into manageable and nonoverlapping categories, all four-digit categories within the ‘‘analgesic’’ two-digit therapeutic class were recoded by staff of the Food and Drug Administration’s Center for Drug Evaluation and Research (CDER). Thus the codes presented in Health, United States do not match the published NDC codes for analgesic therapeutic categories. The NDC contains the following four-digit analgesic therapeutic categories: 1720—general analgesic, 1721—narcotic analgesic, 1722—nonnarcotic analgesic, 1724—antiarthritics, 1723—antimigraine/headache, 1726—central pain syndrome, 1727—Nonsteroidal anti-inflammatory drugs (NSAID), 1728—antipyretic, and 1729—menstrual products. These categories were collapsed into broader and mutually exclusive categories of narcotic analgesics, nonnarcotic analgesics, and NSAIDs. Under the NDC system aspirin is coded as an NSAID because of its anti-inflammatory properties, but also as an analgesic, an antiarthritic, and an antipyretic. In this report aspirin has been recoded into the non-narcotic analgesic category. Aspirin was not included as an NSAID because of its common use for cardiac therapy and its many other indications.

Table XI shows how generic analgesic drugs were reclassified for Health, United States. Analgesic drugs were reclassified based on the product’s main ingredients and/or indication of use. For example, Robitussin AC contains several ingredients, one of which is codeine, a narcotic. However, its main use is not for pain but for cough suppression, and it is therefore categorized as a cough and cold product as opposed to a narcotic analgesic product. Another example is methotrexate, which is used for treating certain neoplastic diseases and severe psoriasis in some formulations but is also used to treat rheumatoid arthritis and therefore appears in the list of nonnarcotic analgesic drugs, which include previously defined ‘‘antiarthritic’’ drugs in Table XI.