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Drug Domain

The drug exposure domain concepts capture records about the utilization of a Drug when ingested or otherwise introduced into the body. A Drug is a biochemical substance formulated in such a way that when administered to a Person it will exert a certain physiological or biochemical effect. The following products are not considered Drugs, but Devices:

  • Radiopharmaceuticals
  • Contrast material for imaging
  • Nutritional products and supplements, including baby formula. In reality that results in the slightly arbitrary and in some cases difficult to ascertain situation that solutions of salts for parental use are Drugs (hydrating patients and maintaining ionic balance), while the addition of nutrients such as glucose or vitamins makes them devices (feeding patients).
  • Products directly derived from blood (e.g. erythocytes or plasma)

Drug domain Concepts should be used in the drug_concept_id of the DRUG_EXPOSURE the DRUG_ERA and the DOSE_ERA (both only at the Ingredient level) tables, or in the value_as_concept_id field of the OBSERVATION or MEASUREMENT table (e.g. for Measurements like “Plasma level”).

Overall Structure

Structure of Drug Domain

The Drug Domain consists of Source Concepts (below the horizontal line), Drugs (Standard Concepts) and Classifications (Classification Concepts). As usual, Source Concepts are non-Standard Concepts that are used as coding schemes in various databases. As such, they are mapped to Standard Concepts.

Standard Concepts are based on the RxNorm and RxNorm Extension vocabularies. All Standard RxNorm and RxNorm Extension Concepts are used in the drug_concept_id fields.

RxNorm is the foundation for the combined Domain space. All valid RxNorm Concepts (invalid_reason is null) are used as Standard Concepts. However, RxNorm only contains Drug Concepts for products sold in the United States. All Concepts derived from international products are availabe in the RxNorm Extension vocabulary. Apart from the different vocabulary_id, both RxNorm and RxNorm Extension form a combined Concept space with identical rules for relationships and Concept Ancestry.

RxNorm and RxNorm Extension Concepts are hierarchical. Therefore the Concepts can also be used as Class Concepts: descendants of any Standard Concept in the CONCEPT_ANCESTOR table can expected to be a correct semantic match in a query. For example, a query for the descendants of an ingredient should turn up all drug products (Clinical Drug or Branded Drug) containing that ingredient.

On top of this combined RxNorm/RxNorm Extension Drug Domain are drug classification systems. These are derived from a variety of different vocabularies. Note: Any classification Concept may exist in different classifications, and therefore cannot be considered as unique. For example, NSAID Analgesics exist with very similar memberships as ETC, VA Class and SNOMED classes. Also note: Only ATC is defined for both RxNorm and RxNorm Extension drugs, and can therefore serve as a universal drug classification system for all drugs. The other classifications are defined for RxNorm, only, and future additions for subsets of RxNorm Extension.

Concept Classes

Those for the Source and Classification Concepts are specific to the source vocabulary (see there). The Concept Classes for the Drug Concepts are based on a subset of RxNorm Term Types:

Term TypeNameConcept Class
PINPrecise IngredientIngredient (standard_concept = NULL)
MINMultiple IngredientsNot implemented
BNBrand NameBrand Name
SCDCSemantic Clinical Drug ComponentClinical Drug Component
SCDFSemantic Clinical Drug FormClinical Drug Form
SCDGSemantic Clinical Dose Form GroupNot implemented
SCDSemantic Clinical DrugClinical Drug or Quantified Clinical Drug
SBDCSemantic Branded Drug ComponentBranded Drug Component
SBDFSemantic Branded Drug FormBranded Drug Form
SBDGSemantic Branded Dose Form GroupNot implemented
SBDSemantic Branded DrugBranded Drug or Quantified Branded Drug
GPCKGeneric PackClinical Pack
BPCKBrand Name PackBranded Pack
DFDose FormDose Form
DFGDose Form GroupNot implemented
PSNPrescribable NameNot implemented
SYSynonymImplemented in the CONCEPT_SYNONYM table
TMSYTall Man Lettering SynonymNot implemented
ETDose Form Entry TermNot implemented

Concepts of the Concept Classses “Clinical Drug” and “Branded Drug” (SCD and SBD) of liquid formulations have their drug strength provided as concentrations, with or without the total quantity provided. That means, many of them exist in pairs. RxNorm does not represent this distinction using different Term Types, however, we defined addtional Concept Classes “Quantified Clincal Drug” and “Quantified Branded Drug” for those drugs where a quantity factor is provided.

In addition to the RxNorm-derived Concept Classes, international coding schemes brake drugs down according to their package or box size. This is due to the fact that prescription drugs are generally sold as prepackaged products, while most prescription drugs in the US get packaged at the time of the prescription filling in the pharmacy. Note, that these boxes are different from the RxNorm packs. Packs represent the smallest unit of drug product combinations, while boxes define the total amount of units sold as a product. In addition to boxes, international coding scheme also distinguish products of different manufacturers or resellers (suppliers). To make those coding schemes work seamlessly with the RxNorm system, additional Concept Classes were defined in the RxNorm Extension vocabulary:

VocabNameIngre dientDrug strengthDose formBrand nameQuantity factorBox sizePack content Supplier
RxNormIngredient x
Clinical Drug Component x x
Clinical Drug Form x x
Clinical Drug x x x
Branded Drug Component x x x
Branded Drug Form x x x
Branded Drug x x x x
Clinical Pack x x
Branded Pack x x x
Rxnorm (not explicit)Quantified Clinical Drug x x x x
Quantified Branded Drug x x x x x
RxNorm ExtensionClinical Drug Box x x x x
Branded Drug Box x x x x x
Quantified Clinical Box x x x x x
Quantified Branded Box x x x x x x
Clinical Pack Box x x x x
Branded Pack Box x x x x x
Marketed Product x x x optionaloptionaloptionaloptional x

This system of Concept Classes is fully normalized. I.e. that for each defined, say, Branded Drug there are the equivalent Clinical Drug, Clinical Drug Component, Branded Drug Component, Clinical Drug Form and Branded Drug Form available. For combination drugs with several Ingredients equivalent combinations are defined in the same manner. Note that the latter is not true for Clinical Drug Components. These only exist as single-ingredient Concepts. The reason for this is not discussed in the technical documentation by RxNorm. Ingredients are only defined as single Ingredients, RxNorm's MIN (Multiple Ingredients) are not implemented.


As usual, all Source Concepts are mapped to the RxNorm or RxNorm Extension Concepts. The mapping is either constructed from the vocabulary source and in some cases curated by the vocabulary team. Generally, mappings are between equivalent Concept Classes, and if possible to Clinical or Branded Drugs, or more detailed Concept Classes further down in the hierarchy. However, in some cases this is not possible (e.g. when mapping Procedure Drugs) or if insufficient information is known about a Source Concept, at which point a more general Concept can be used. Such non-equivalent mappings are carried out as following:

  • One-to-many mappings to Ingredients or Clinical Drug Components
  • One-to-one mappings to all other Concept Classes

The internal relationships between Drug Concepts are derived from RxNorm relatinships and extended to cover the additional Concept Classes of the RxNorm Extension vocabulary (“Drug” without any attribute means either “Clinical” or “Branded”):

SourceOriginal namerelatinship_idConnecting Concept Classes
RxNormconsists_ofConsists ofDrug or Quantified Drug and Drug Component
constitutesConstitutesDrug Component and Drug or Quantified Drug
contained_inContained inDrug or Quantified Drug and Pack
containsContainsPack and Drug or Quantified Drug
dose_form_ofRxNorm dose form ofDose Form and Drug, Drug Form
form_ofForm of(Precise) Ingredient and Ingredient
has_dose_formRxNorm has dose formDrug, Drug Form and Dose Form
has_formHas formIngredient and (Precise) Ingredient
has_ingredientRxNorm has ingClinical Drug Form/Component and Ingredient, and Branded Drug Form/Component and Brand Name. Not implemented between Branded Drug and Brand Name
has_precise_ingredientHas precise ingBrand Name/Clinical Drug Component and (Precise) Ingredient
has_quantified_formHas quantified formDrug and Quantified Drug
has_tradenameHas tradenameClinical and Branded Concept Class equivalents
has_tradenameHas brand nameIngredient and Brand Name
ingredient_ofRxNorm ing ofIngredient and Clinical Drug Form/Component, and Brand Name and Branded Drug Form/Component. Not implemented between Branded Drug and Brand Name
inverse_isaRxNorm inverse is aDrug Form and Drug
isaRxNorm is aDrug and Drug Form
precise_ingredient_ofPrecise ing of(Precise) Ingredient and Brand Name/Clinical Drug Component
quantified_form_ofQuantified form ofQuantified Drug and Drug
reformulated_toReformulated inBrand Name and Brand Name (name changes)
reformulation_ofReformulation ofBrand Name and Brand Name (name changes)
tradename_ofTradename ofBranded and Clinical Concept Class equivalents
tradename_ofBrand name ofBrand Name and Ingredient
- Concept replaced byConcepts in RXNATOMARCHIVE with merged_to_rxcui information
- Concept replacesConcepts in RXNATOMARCHIVE with merged_to_rxcui information
RxNorm Extension - Available as boxDrug and Drug Box
- Box ofDrug Box and Drug
- Has marketed formDrug and Marketed Product
- Marketed form ofMarketed Product and Drug
- Has supplierDrug and Supplier
- Supplier ofSupplier and Drug

For a discussion of the relationships between Drugs and Classifications and within Classifications please see the individual vocabulary sections.

Drug Strength

The Drug Domain has an additional DRUG_STRENGTH table defining the strength of each ingredient. This is defined for all Drug Concept Classes except Ingredient, Clinical Drug Form and Branded Drug Form, Dose Form, Brand Name and Supplier.

documentation/vocabulary/drug.txt · Last modified: 2016/07/26 14:51 by cgreich