ATC - History of the WHO ATC system

In 1969, the Drug Utilisation Research Group (DURG) was formed from a group of expert WHO advisers due to a perceived need for an internationally accepted classification system that could be used in drug consumption studies. By modifying and extending the European Pharmaceutical Market Research Association (EPhMRA) classification system, Norwegian researchers in collaboration with the Norwegian Medicinal Depot (NMD) developed the system known as the ATC classification. A technical unit of measurement called the Defined Daily Dose (DDD) was also developed. The DDD is defined as "the assumed average maintenance dose per day for a drug used for its main indication in adults". The Nordic Council on Medicines (NLN) further developed the ATC/DDD system together with NMD. The ATC/DDD methodology was used for the first time in a 1976 publication "Nordic Statistics on Medicines".

In 1981, the WHO Regional Office for Europe recommended the ATC/DDD system for international drug utilisation studies. A body responsible for co-ordinating the use of the methodology, the WHO Collaborating Centre for Drug Statistics Methodology, was established in Oslo in 1982. The Centre is now located at the Norwegian Institute of Public Health and is funded by the Norwegian government.

Since 1996, WHO Headquarters recommend the ATC system for global drug utilisation studies. Recently it was decided that the WHO Essential Drug List should also be based on the ATC classification system to support more widespread use of the system (2). WHO Collaborating Centres involved in drug monitoring use the ATC system for classification and statistics. The WHO Collaborating Centre for International Drug Monitoring (Uppsala Monitoring Centre) in Sweden maintains the WHO Drug Dictionary (3), a database with entries for most drugs used in countries participating in the WHO Programme for International Drug Monitoring (4).

In addition to the use of ATC/DDD as a tool for drug utilisation statistics and research, in some countries the ATC system is used in clinical settings together with the International Statistical Classification of Diseases (ICD). The main advantage in clinical use is that the ATC classification allows for more specific and up-to-date information on particular drugs/substances than ICD alone. In these cases, national ICD coding guidelines have been developed to allow the possibility to use supplementary ATC codes to specify medical substances responsible for poisoning or adverse drug effects. For example, in Denmark, Finland, Iceland, Norway and Sweden the national ICD coding guidelines state that supplementary ATC codes may be used with ICD-10 codes where relevant. The details of national guidelines as well as registration practice may vary depending on the type of registration and reporting needed in different clinical settings and in current patient administrative systems.