The ATC system

The current regulations for the ATC system (Anatomical Therapeutic Chemical Classification System), which is a system for the classification of medicinal products according to their primary active substance and area of impact, are defined by the WHO Collaborating Centre for Drug Statistics in 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 list 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 the analgesic substance acetylsalicylic acid with the ATC code N02BA01 may serve to illustrate the structure of the ATC system:

N Nervous system (anatomical main group, 1st level)
02 Analgesics (therapeutic subgroup, 2nd level)
B Other analgesics and antipyretics (therapeutic/pharmacological subgroup, 3rd level)
A Salicylic acid and derivatives (chemical/therapeutic/pharmacological subgroup, 4th level)
01 Acetylsalicylic acid (subgroup for chemical substances, 5th level)

The ATC code of a medicinal product may change, for example if the main indication for the substance is altered
Such changes are published with effect as of 1 January. The present statistics refer to the ATC codes applicable in 2010. A complete list of all active substances for which the ATC codes changed in the period 1996 to 2010 is available in appendix 1 (PDF file, opens in a new window).

A few medicinal products have an incomplete ATC code
It may apply to medicines recently marketed, why the complete ATC code may not yet be determined. Such products are therefore registered on the 3rd or 4th level for a period of time. In the data for the current statistics, any incomplete ATC codes are lengthened with stars (“ * “) for the 5th level. Thus, the sale of these medicines can also be found at the 5th level. For instance, medicinal products with the incomplete ATC code “G03AA” are shown under the name “GA03AA**”.

Some medicinal products cannot be assigned an ATC code
This especially applies to magistral medicinal products, i.e. medicines manufactured at pharmacies – and often in relatively small quantities. The sale of magistral medicinal products is quite modest in the primary health sector, whereas it is of much greater significance in the hospital sector.

Danish hospitals have introduced coordinated product codes for a number of magistral medicinal products. Because of this, it has become possible to assign ATC codes to some of the magistral products.

However, it is not possible to assign ATC codes to a few pharmaceutical specialties dispensed under a special permission pursuant to section 25 of the Danish Medicines Act.

DDD values
When calculating medicinal product sales in quantities, the WHO-established defined daily dose (DDD) is used. The DDD is the assumed average dose per day for a medicinal product used for its main indication in adults. Using DDDs as a unit of measurement enables comparison of the consumption between different medicinal products, independent of e.g. different strengths.

The DDD values can be found at http://www.whocc.no/atcddd.

The WHO classification does not specify a DDD value for combination products or products for which the DDD is difficult to indicate as quantity of active substance. Products without a DDD assigned by the WHO but with a national DDD are listed in appendix 3 (PDF file, opens in a new window). The nationally assigned values are also used for calculating quantity consumption in the Register of Medicinal Product Statistics.

For combination products with an assigned DDD, the DDD value may be smaller than the sum of the DDD for each of the individual substances. A drop in total DDD consumption within a drug class may therefore be because part of the consumption is “moved” from individual substance products to combination products.

For medicinal products without a DDD assigned either by the WHO or nationally (appendix 3 (PDF file, opens in a new window)) sales are only represented by means of turnover.

The DDD value of a medicine may change if the use or dosage of the product is reviewed. Normally, changes are introduced once a year as of 1 January. In the present statistics, the quantity is calculated based on the DDD values applicable in 2010. A list of the active substances for which the DDD value changed from 1996 to 2010 is available in appendix 2 (PDF file, opens in a new window).

Danish Medicines Agency, last updated on 26 May 2010