Advantages of using WHO Drug ATC Classification for Disproportionality Analysis

WHO Drug Anatomical Therapeutic Chemical (ATC) Classification organizes drugs into 14 major groups. These groups are further sub-classified into 3 more levels*. These ATC levels help to identify similar therapeutic drugs in a broad or narrower group. These ATC levels can also help in the disproportionality analysis of drug-adverse events.

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The key advantages are,

1. WHO Drug ATC Classification offers hierarchical therapeutic groups to analyze the drug with a narrow or broader group of drugs.

2. ATC levels provide a head-start for understanding drug-event incidences in comparison to relevant drugs in the same class.

The diagram below shows the drug Acarbose grouped under Alpha glucosidase inhibitors (ATC level 4), and the higher levels are Blood glucose lowering drugs, excl. insulins (level 3), Drugs used in diabetes (level 2), and Alimentary tract and metabolism (level 1).

Fig 1. WHO Drug Dictionary ATC Hierarchy

The population of reports used in the disproportional analysis changes with ATC levels, but the number of reports for the specific drug-event pair is the same. Performing disproportionate analysis using the ATC levels provides insights into the adverse events reported by other patients in different levels of ATC classification.

The following diagram represents the drug-event pair viewed within different levels of the WHO Drug Dictionary ATC Levels.

Fig 2. Drug-Event represented within ATC Levels

You can still analyze the drug-event pair with all reports submitted to the FAERS using the fictitious level 0.

* Some drugs may not have all 4 levels of ATC classification.