The ATC system

The Anatomical Therapeutic Chemical (ATC) classification system is a system for classification of medicinal products according to their primary constituent and to the organ or system on which they act and their chemical, pharmacological and therapeutic properties. The current rules for the ATC system are defined by the WHO Collaborating Centre for Drug Statistics, Oslo, Norway.

1st level of the ATC system:

A: Alimentary tract and metabolism
B: Blood and blood forming organs
C: Cardiovascular system
D: Dermatologicals
G: Genito urinary system and sex hormones
H: Systemic hormonal preparations, excl. sex hormones and insulins
J: Antiinfectives for systemic use
L: Antineoplastic and immunomodulating agents
M: Musculo-skeletal system
N: Nervous system
P: Antiparasitic products, insecticides and repellents
R: Respiratory system
S: Sensory organs
V: Various

The system divides human medicinal products into fourteen anatomical main groups (1st level – see the above) with one therapeutic/pharmacological subgroup (2nd level), two chemical/therapeutic/pharmacological subgroups (3rd and 4th level) and a subgroup for chemical substances (5th level).

A complete classification of metformin with the ATC code A10BA02 may serve to illustrate the structure of the ATC system:

The ATC code for a medicinal product may change, for example if the primary indication for the substance is altered
Such changes are published with effect as of 1 January. The present statistics refer to the ATC codes current in 2007. This means that it is possible to make an immediate comparison with new statements of sale of medicinal products in 2007. A complete list of all active substances for which the ATC codes changed in the period 1998 to 2007 is available in appendix 1 (see "Bilag 1" PDF file, opens in a new window).

A few medicinal products do not have a complete ATC code
This may apply to medicinal products recently marketed and for which the complete ATC code is not yet determined. Therefore, such products are registered on the 3rd or 4th level for a certain period. When drawing up the data for the present statistics, incomplete ATC codes have been lengthened by stars (“ * ”) for the 5th level. Thus, the sale of these medicinal products can be found at the 5th level. For instance, medicinal products with the incomplete ATC code “G03AA” are shown under the name “GA03AA**”.

For some medicinal products it is not possible to assign an ATC code
This especially applies to magistral medicinal products. This kind of medicinal products is manufactured at pharmacies – and often in relatively small quantities. In the primary healthcare sector, the sale of magistral medicinal products is quite modest, whereas it is much more significant in the hospital sector.
Coordinated product numbers have been introduced for a number of magistral medicinal products in hospitals. Because of this, it has become possible to assign ATC codes to some of the magistral products.
Nor is it possible to assign an ATC code to a few pharmaceutical specialties that are dispensed according to a special permission pursuant to section 25 of the Danish Medicines Act.

DDD values
The WHO has established the defined daily dose (DDD), which is used for indicating medicinal product sales in quantities. The defined daily dose for a medicinal product is determined according to an assumed average dose per 24 hours for an adult using the product for its main indication. By using defined daily doses as a measure, it becomes possible to compare the consumption of different medicinal products regardless of differences in potency, etc.
The DDD values are available at http://www.whocc.no/atcddd .

In the WHO classification, no DDD value is stated for combination preparations or preparations for which DDD is difficult to indicate as quantity of active substance. Preparations that have not been assigned a DDD by the WHO but which have been assigned a national DDD are available in appendix 3 (see "Bilag 3" PDF file, opens in a new window). The nationally assigned values are also used for calculating quantity consumption in the present publication.
For medicinal products not assigned a DDD either by the WHO or nationally (appendix 3 (see "Bilag 3" PDF file, opens in a new window)) sales are only represented by means of turnover.
The DDD value of a medicinal product may change if the use or dosage of the preparation is reviewed. Normally, changes are introduced once a year as of 1 January. In the present statistics, the quantity is established based on the DDD values current in 2007. A list of the active substances for which the DDD value changed from 1998 to 2007 is available in appendix 2 (see "Bilag 2", PDF file, opens in a new window).