Anatomical Therapeutic Chemical Classification System

The Anatomical Therapeutic Chemical (ATC) Classification System is a global drug classification system that categorizes pharmaceutical drugs based on their anatomical, therapeutic, pharmacological, and chemical properties. It is maintained by the World Health Organization (WHO) Collaborating Centre for Drug Statistics Methodology (WHOCC) and serves as an essential tool for drug utilization research, facilitating the comparison and analysis of medication usage across different healthcare systems.

Overview

The ATC system provides a standardized framework for classifying drugs by organizing them into a hierarchical structure. This classification is based on:

• The anatomical organ system the drug primarily affects.
• The therapeutic purpose for which it is used.
• Its pharmacological characteristics and mechanism of action.
• Its chemical properties and molecular composition.

A key feature of the ATC system is that different brands containing the same active ingredient and indications are assigned the same code. Similarly, a single ATC code may represent a combination of substances used for a specific indication. For example, acetylsalicylic acid (aspirin) has multiple ATC codes:

• ATC code A01AD05 – For use in oral treatments.
• ATC code B01AC06 – As a platelet inhibitor.
• ATC code N02BA01 – As an analgesic and antipyretic.

Additionally, some ATC codes represent a combination of active ingredients, such as ATC code C09BB04, which designates the combination of perindopril and amlodipine. When these components are used individually, they have separate ATC codes.

History

The ATC system evolved from earlier pharmaceutical classification models, particularly the Anatomical Classification System, which was initially designed for industry use. In 1971, the European Pharmaceutical Market Research Association (EphMRA) introduced an early version of ATC, which classified drugs into four hierarchical levels. This system was later refined by the WHO, and in 1976, the modern ATC system was officially established with the addition of a fifth level for increased specificity.

Classification

The ATC system consists of five hierarchical levels that progressively define a drug’s classification:

First Level: Anatomical Main Group

The first level is represented by a single letter and consists of 14 main anatomical groups:

Code	Description
A	Alimentary tract and metabolism
B	Blood and hematopoietic system
C	Cardiovascular system
D	Dermatologicals
G	Genitourinary system and sex hormones
H	Systemic hormonal therapy, excluding sex hormones and insulins
J	Anti-infective agents for systemic use
L	Antineoplastic and immunomodulating agents
M	Musculoskeletal system
N	Nervous system
P	Antiparasitic products, insecticides, and repellents
R	Respiratory system
S	Sense organs
V	Various drug categories

Second Level: Therapeutic Main Group

This level, represented by two numbers, classifies drugs based on their therapeutic use. For instance:

• ATC code N05 – Psycholeptics (drugs that affect the central nervous system).

Third Level: Pharmacological Subgroup

Represented by a single letter, this level defines the pharmacological class of drugs. Example:

• ATC code N05B – Anxiolytic medications.

Fourth Level: Chemical/Pharmacological Subgroup

Also represented by a single letter, this level specifies the chemical subgroup of the drug. Example:

• ATC code N05BA – Benzodiazepine derivatives.

Fifth Level: Chemical Substance

This final level, represented by two numbers, identifies the specific active ingredient. Example:

• ATC code N05BA01 – Diazepam.

Application and Usage

The ATC system is widely used for multiple purposes in healthcare, pharmaceutical research, and drug regulation:

• Drug utilization studies – Helps track medication use trends and supports pharmacovigilance efforts.
• Prescribing guidelines – Assists healthcare professionals in ensuring appropriate drug use based on classifications.
• International drug comparison – Enables uniform comparisons of drug usage across different countries and healthcare systems.
• Reimbursement policies – Used by health insurance providers and government agencies to standardize drug pricing and reimbursement policies.
• Public health research – Supports epidemiological studies related to medication consumption.

Limitations

While the ATC system is a robust classification model, it has some limitations:

• Variability in classification – Some drugs may have multiple ATC codes depending on their use.
• Region-specific modifications – Different countries may apply slight modifications to the system for local regulatory purposes.
• Complex combinations – Drug combinations may not always be adequately classified under a single ATC code.

See Also

• World Health Organization
• Pharmacovigilance
• Drug utilization research
• International drug nomenclature
• Essential medicines

External Links

• WHO Collaborating Centre for Drug Statistics Methodology
• WHO ATC/DDD Index
• European Medicines Agency