APPLICATIONS
RxClass includes a source of drug-class relations that maps active RxNorm drug products to the Anatomical Therapeutic Chemical (ATC) drug classification. Its name in RxClass is ATCPROD.
ATCPROD is developed by the National Library of Medicine (NLM) to support the unambiguous classification of RxNorm drug products to the Anatomical Therapeutic Chemical (ATC) drug classification. The main purpose of ATCPROD is to facilitate drug analytics, especially the analysis of medication datasets from observational data.
The version of ATC published by WHO associates drug ingredients with classes. However, inferring the ATC class of a drug product from that of its ingredient(s) alone can be problematic. For example, through its ingredient timolol, an eye drop formulation can be associated with both ophthalmological and cardiovascular ATC classes, while only the ophthalmological class is applicable here. Similarly, while aspirin is associated with multiple ATC classes, low-dose aspirin products should generally be associated with ATC class platelet aggregation inhibitors, not analgesics. Moreover, while ATC classifies candesartan and hydrochlorothiazide individually, it does not explicitly list the combination of candesartan and hydrochlorothiazide. In order to assign such combination products to the class candesartan and diuretics, ATC users have to first associate hydrochlorothiazide with diuretics.
In contrast to the native ATC classification, in which ingredients are associated with classes, ATCPROD directly assigns ATC classes to RxNorm products, considering not only their ingredient(s), but also their strength and dose form, and whether they are used in combination with other ingredients. Moreover, ATCPROD interprets the ATC guidelines to assign products to the appropriate ATC class in cases when individual ingredients (or ingredient combinations) are not explicitly listed as class members (primarily for multi-ingredient drug products).
NLM assigns ATC classes to RxNorm drug products. The classification is updated each year when a new version of ATC is released. Additionally, it is updated to reflect changes in RxNorm with each monthly release.
ATCPROD aims to classify the generic products (including packs) in a given release of the RxNorm Current Prescribable subset, to the extent an ATC class is applicable. A single class is assigned to a given product (with an effort to reflect the most common indication for a product). The class assigned to a generic product is also assigned to the corresponding branded product, as brand is never a factor in ATC classification.
The ATCPROD classification of RxNorm products whose ingredients are unambiguously and explicitly classified in ATC generally mimics the ATC classification. The added value of ATCPROD is mainly for those drug products whose ingredients lead to multiple classes in ATC (e.g., depending on the strength or dose form of the product) and for products whose ingredients (or ingredient combinations) are not explicitly listed in ATC. Such products are classified by rules (e.g., strength or dose form rules) and reviewed by experts. Of note, the ATCPROD classification is generally consistent with the VA classification of drug products.
In our experience, ATCPROD covers over 95% of the drugs found in large prescription datasets, such as MEDICARE.
ATCPROD is available through RxNav (under the Classes tab when searching for drug products). ATCPROD is the default classification system for ATC in RxClass, where the corresponding products are listed. Finally, RxNorm drug products can be classified to ATCPROD with RxMix and through the RxNorm API for processing large prescription datasets.
Of note, while the scope of ATCPROD is current RxNorm products, ATCPROD can be used for drug analytics of longitudinal datasets (i.e., with obsolete drug codes) with help from RxNorm API functions, such as findActiveProducts.