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The Anatomical Therapeutic Chemical (ATC) Classification System is a drug classification system that classifies the active ingredients of drugs according to the organ or system on which they act and their therapeutic, pharmacological, and chemical properties. It is controlled by the World Health Organization Collaborating Centre for Drug Statistics Methodology (WHOCC). Inasmuch as the ATC codes are semantic identifiers, the ATC vocabulary was taken as a basis for the OMOP Drug Hierarchy. As of 30 September 2021, there are 6497 valid codes in the ATC.
ATC source codes are obtained from WHOCC ATC/DDD Index 2021 and, in OMOP, stored in the table of class_drugs_scraper
The translation of source ATC codes to the OMOP Vocabulary is presented on the OHDSI GitHub.
ATC codes are alphanumeriс entities of different length, which reflects their Class:
ATC Class | Length | Code example |
---|---|---|
1st | 1 character | A |
2nd | 3 characters | A01 |
3rd | 4 characters | A01A |
4th | 5 characters | A01AA |
5th | 7 characters | A01AA01 |
All ATC codes are of the Drug domain, however, they may be hierarchically connected to the Device or Observation (concept_class_id = ‘Substance’) domains.
concept_class_id | description | count |
---|---|---|
ATC 5th | Chemical substance subgroup (ingredients or combinations) | 5131 |
ATC 4th | Therapeutic/pharmacological/chemical subgroup | 890 |
ATC 3rd | Pharmacological subgroup | 267 |
ATC 2nd | Therapeutic subgroup | 94 |
Valid ATC codes are Classifications, invalid ATC codes are Non-standard ones.
The source usually supplies replacement ATC codes for those which have been deprecated. However, there are several ATC Classes without replacement (they seem to be semantically wrong or being erroneously placed into the ATC hierarchy).
Relationships are defined within ATC and between ATC and RxNorm, RxNorm Extension, Multilex, SNOMED, NDFRT, and VA Class.
The ATC vocabulary is the hierarchical terminology, in which “the lowest” 5th ATC Drug Classes, reflecting real Drug Products, are connected to “higher” ATC Classes (from the 4th to 1st) via the one-step ancestry. In OMOP, the original ATC hierarchy is extended by Standard Drug Products of RxNorm and RxNorm Extension vocabularies, which are assigned to be descendants of the 5th ATC Classes.
atc.adm_r | omop.adm_r |
---|---|
implant | implant |
Inhal | inhalant |
Inhal. powder | |
Inhal.aerosol | |
Inhal.powder | |
Inhal.solution | |
Instill.sol. | instillation solution |
intravesical | intravesical |
N | nasal |
O | local oral* |
O | oral |
O, P | systemic |
Opht | ophthalmic |
oral aerosol | local oral |
P | parenteral |
R | rectal |
s.c. implant | implant |
SL | sublingual |
T | topical |
TD patch | transdermal |
V | vaginal |