European Research Association for Pharmaceutical Market and an international group have developed the ADC Drug Classification system, which is recommended by the World Health Organization (WHO). It has been in use since 1987. According to this classification, drugs are grouped into fourteen basic groups according to the organic system of the organism where they work. These fourteen anatomical groups represent the first anatomical level and is labeled with one capital letter, as follows: 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 J General antiinfectives for systemic use L Antineoplastic and immunomodulating agents M Muscle-skeletal system N Nervous system P Antiparasitic products, insecticides and repellents R Respiratory system S Sensory organs V Various. Drugs are further divided into therapeutic groups and subgroups (2nd and 3rd level), the 4th level is the chemical-therapeutic subgroup. The 5th level is the generic drug name. Each drug is represented by 7 numeric-character bytes code. These seven bytes are determining the group (1st anatomical classification level marked by a capital letter) with the corresponding therapeutic subgroups on the 2nd and 3rd classification level, 4th level labels the chemical-therapeutic subgroup, while the 5th level is signified by the individual chemical compounds (generic name) and is marked by an Arabic number. The importance of the ATC classification is the possibility of the international comparability, monitoring of the use and consumption from various aspects. The standardized monitoring methodology incorporates too the daily doze determining methodology (DDD). Defined Daily Dose (DDD) is the drug amount used for the most common indication, and is, therefore, the basic statistical unit of drug use monitoring. It represents not only the recommended doze, but is also the only means of acquiring the number of patients receiving that particular drug (DDD per 1000 inhabitants). This makes the basis for the comparability of drug use in various places (country, region, institution, etc.).