TheAnatomical Therapeutic Chemical (ATC)Classification System is adrug classification system that classifies theactive ingredients ofdrugs according to theorgan orsystem on which they act and theirtherapeutic,pharmacological andchemical properties. Its purpose is an aid tomonitor drug use and forresearch to improve quality medication use. It does not implydrug recommendation orefficacy.[1] It is controlled by theWorld Health Organization Collaborating Centre for Drug Statistics Methodology (WHOCC), and was first published in 1976.[2][3][4]
Thispharmaceutical coding system divides drugs into different groups according to the organ or system on which they act, theirtherapeutic intent or nature, and the drug'schemical characteristics. Different brands share the same code if they have the same active substance and indications. Each bottom-level ATC code stands for a pharmaceutically used substance, or a combination of substances, in a single indication (or use). This means that one drug can have more than one code, for exampleacetylsalicylic acid (aspirin) hasA01AD05 (WHO) as a drug for localoral treatment,B01AC06 (WHO) as aplatelet inhibitor, andN02BA01 (WHO) as ananalgesic andantipyretic; as well as one code can represent more than one active ingredient, for exampleC09BB04 (WHO) is the combination of perindopril with amlodipine, two active ingredients that have their own codes (C09AA04 (WHO) andC08CA01 (WHO) respectively) when prescribed alone.
The ATC classification system is a strict hierarchy,[5] meaning that each code necessarily has one and only one parent code, except for the 14 codes at the topmost level which have no parents. The codes are semantic identifiers,[5] meaning they depict information by themselves beyond serving as identifiers (namely, the codes depict themselves the complete lineage of parenthood). As of 7 May 2020, there are 6,331 codes in ATC; the table below gives the count per level.[6]
| ATC level | Codes | Different names/pharmaceuticals |
|---|---|---|
| Level 1 | 14 | 14 |
| Level 2 | 94 | 94 |
| Level 3 | 267 | 262 |
| Level 4 | 889 | 819 |
| Level 5 | 5067 | 4363 |
The ATC system is based on the earlier Anatomical Classification System, which is intended as a tool for the pharmaceutical industry to classify pharmaceutical products (as opposed to their active ingredients).[7] This system, confusingly also called ATC, was initiated in 1971 by theEuropean Pharmaceutical Market Research Association (EphMRA) and is being maintained by the EphMRA and Intellus. Its codes are organised into four levels.[8] The WHO's system, having five levels, is an extension and modification of the EphMRA's. It was first published in 1976.[2]
In this system, drugs are classified into groups at five different levels:[9]
The first level of the code indicates the anatomical main group and consists of one letter. There are 14 main groups:[10]
| Code | Contents |
|---|---|
| A | Alimentary tract andmetabolism |
| B | Blood andblood forming organs |
| C | Cardiovascular system |
| D | Dermatologicals |
| G | Genito-urinary system andsex hormones |
| H | Systemichormonal preparations, excluding sex hormones and insulins |
| J | Antiinfectives for systemic use |
| L | Antineoplastic andimmunomodulating agents |
| M | Musculo-skeletal system |
| N | Nervous system |
| P | Antiparasitic products,insecticides andrepellents |
| R | Respiratory system |
| S | Sensory organs |
| V | Various |
Example:CCardiovascular system
The second level of the code indicates the therapeutic subgroup and consists of two digits.[11]
The third level of the code indicates the therapeutic/pharmacological subgroup and consists of one letter.
Example: C03C High-ceiling diuretics
The fourth level of the code indicates the chemical/therapeutic/pharmacological subgroup and consists of one letter.
Example: C03CASulfonamides
The fifth level of the code indicates the chemical substance and consists of two digits.
Example: C03CA01furosemide
TheAnatomical Therapeutic Chemical Classification System for veterinary medicinal products (ATCvet) is used to classifyveterinary drugs. ATCvet codes can be created by placing the letter Q in front of the ATC code of most human medications. For example, furosemide for veterinary use has the codeQC03CA01.
Some codes are used exclusively for veterinary drugs, such asQI Immunologicals,QJ51 Antibacterials for intramammary use orQN05AX90amperozide.[12]
The Herbal ATC system (HATC) is an ATC classification ofherbal substances; it differs from the regular ATC system by using 4 digits instead of 2 at the 5th level group.[13]
The herbal classification is not adopted by WHO. TheUppsala Monitoring Centre is responsible for the Herbal ATC classification, and it is part of theWHODrug Global portfolio available bysubscription.[14]
The ATC system also includes defined daily doses (DDDs) for many drugs. This is a measurement of drug consumption based on the usual daily dose for a given drug. According to the definition, "[t]he DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults."[15]
National issues of the ATC classification, such as theGermanAnatomisch-therapeutisch-chemische Klassifikation mit Tagesdosen, may include additional codes and DDDs not present in the WHO version.[16]
ATC follows guidelines[17] in creating new codes for newly approved drugs. An application is submitted to WHO for ATC classification and DDD assignment. A preliminary or temporary code is assigned and published on the website and in theWHO Drug Information for comment or objection. New ATC/DDD codes are discussed at the semi-annual Working Group meeting. If accepted it becomes a final decision and published semi-annually on the website andWHO Drug Information and implemented in the annual print/on-line ACT/DDD Index on January 1.[18]
Changes to existing ATC/DDD follow a similar process to become temporary codes and if accepted become a final decision as ATC/DDD alterations. ATC and DDD alterations are only valid and implemented in the coming annual updates; the original codes must continue until the end of the year.[19][20] An updated version of the complete on-line/print ATC index with DDDs is published annually on January 1.[21]
