The 2nd, 3rd and 4th levels are often used to identify pharmacological subgroups when that is considered more appropriate than therapeutic or chemical subgroups.
The complete classification of metformin illustrates the structure of the code:
Thus, in the ATC system all plain metformin preparations are given the code A10BA02.
For the chemical substance, the International Nonproprietary Name (INN) is preferred. If INN names are not assigned, USAN (United States Adopted Name) or BAN (British Approved Name) names are usually chosen.
The coding is important for obtaining accurate information in epidemiological studies. The five different levels allow comparisons to be made at various levels according to the purpose of the study.
