OBJECTIVES: The National Drug Code (NDC) Directory by the Food and Drug Administration (FDA) is a publicly available, and frequently used in pharmacoepidemiologic to identify prescription drug usage. The current study compared the FDA NDC Directory data and Micromedex Redbook^® in identifying frequently prescribed medication records in nationally representative utilization data using the NDC generic name mapping tables.

METHODS: The study included the records from the 2017-2018 Medical Expenditure Panel Survey Household Component (MEPS-HC) prescribed medicine file. Records for the top 50 most prescribed medications were retained based on the generic name. Records with a missing NDC code were removed. The NDC to generic name mapping tables from FDA NDC directory and Micromedex Redbook® were separately implemented for the previously identified records. For each of the 50 most prescribed medications, the proportion of records identifiable using the FDA NDC directory and Micromedex Redbook® mapping table were tabulated.

RESULTS: The study identified an unweighted sample of 349,641 prescription records representing 3.56 billion annualized records nationally. Micromedex Redbook® based NDC to generic name mapping tables identified 99.88 prescription records, whereas the FDA NDC directory based mapping tables only identified 90.95% of the records. The performance of FDA NDC directory based mapping tables varied across different drugs and was lowest for human insulin (55.65%), followed by warfarin (56.43%), clonazepam (60.89%), norgestimate (65.82%), and levothyroxine (69.91%).

CONCLUSIONS: The coverage by the publicly available FDA NDC directory based mapping table for the 50 most frequently prescribed medications was variable and incomplete. Micromedex Redbook®, in contrast, provides complete coverage of the 50 most frequently prescribed medications. Researchers should carefully select drug knowledge base sources for pharmacoepidemiology research.