Introduction

The ATC system for classifying drugs is widely used in European countries. ATC classifications are available online, and are updated and published once a year by the World Health Organization Collaborating Centre for Drug Statistics Methodology ( WHO Collaborating Centre for Drug Statistics Methodology Web Site at: http://www.whocc.no/ ). The ATC system and its associated Defined Daily Dose as a measuring unit are recommended by the WHO for drug utilization studies. The ATC system is becoming used more commonly in Canada.

The ATC classification is a component of the Health Canada Drug Product Database. See the Health Canada Web Site on the Drug Product Database (DPD): http://www.hc-sc.gc.ca/dhp-mps/prodpharma/databasdon/terminolog-eng.php for more information.

A link to the Health Canada Web Site - Drug Product On-Line Query Tool using 5 or 7 digit ATC codes is provided below.

Classification Levels

In the ATC classification system, drugs are divided into different groups according to the organ or system on which they act and their chemical, pharmacological and therapeutic properties. Drugs are classified into groups at 5 different levels:


• 1st level - At the broadest level, drugs are divided into one of the following fourteen anatomical groups. The first level of the code is based on a letter e.g. "B" for Blood and blood forming organs:

  Level	Main Group
  A	Alimentary tract & metabolism
  B	Blood & blood forming organs
  C	Cardiovascular system
  D	Dermatologicals
  G	Genitourinary system & sex hormones
  H	Systemic hormonal preparations
  J	Antiinfectives for systemic use
  L	Antineoplastic & immunomodulating agents
  M	Musculo-sketal system
  N	Nervous system
  P	Antiparasitic products
  R	Respiratory system
  S	Sensory organs
  V	Various

• 2nd level - is either a pharmacological or therapeutic subgroup (e.g., "B03" for Anti-anemic preparations).
  
  
• 3rd level - is a chemical or therapeutic or pharmacological subgroup (e.g., "B03A" for Iron Preparations).
  
  
• 4th level - is a chemical or therapeutic or pharmacological subgroup. This is the level used to count "number of different drugs" as it is the level which aggregates drugs just above their descriptive chemical substance, (e.g., "B03AA" for Iron, bivalent, oral preparations). A count of an individual's drugs at the fourth level of ATC gives the researcher a categorical option with which to stratify and then describe pharmaceutical users. It approximates a measure of comorbidity.
  
  
• 5th level - is the subgroup for the chemical substance (e.g., "B03AA07" Ferrous sulphate).

In the ATC system all DINs (drug identification numbers) with the generic name "ferrous sulphate" would be assigned the code B03AA07. In other words, an ATC code has five levels that are described by seven digits.