RxNorm Overview

I. Introduction and Overview

What is RxNorm?

RxNorm, a standardized nomenclature for clinical drugs, is produced by the National Library of Medicine (NLM). In this context, a clinical drug is a pharmaceutical product given to (or taken by) a patient with a therapeutic or diagnostic intent. In RxNorm, the name of a clinical drug combines its ingredients, strengths, and form.

While ingredient and strength have straightforward meanings, clarification of what is meant by form is in order. In RxNorm, the form is the physical form in which the drug is administered or is specified to be administered in a prescription or order. The RxNorm clinical drug name does not refer to the size of the package, the form in which the product was manufactured, its form when it arrived at the dispensary, or the route of administration of the drug..

RxNorm’s standard names for clinical drugs are connected to the varying names of drugs present in many different controlled vocabularies within the Unified Medical Language System (UMLS) Metathesaurus, including those in commercially available drug information sources. These connections are intended to facilitate interoperability among the computerized systems that record or process data dealing with clinical drugs.

A Simple Idea Implemented Rigorously

RxNorm is organized around concepts with normalized names for clinical drugs. These names contain information on ingredients, strengths, and dose forms. For example:

Acetaminophen 500 MG Oral Tablet                      for a generic drug name
Acetaminophen 500 MG Oral Tablet [Tylenol]         for a branded drug name

Within RxNorm, generic and branded normalized forms are related to each other and to the names of their individual components by a well-defined set of named relationships. Thus, Acetaminophen 500 MG Oral Tablet is related to Acetaminophen 500 MG Oral Tablet [Tylenol], and both have relationships to Acetaminophen, Acetaminophen 500 MG, and Oral Tablet. Within the UMLS Metathesaurus, Acetaminophen 500 MG Oral Tablet and Acetaminophen 500 MG Oral Tablet [Tylenol] will each be linked to different names that are used for these entities in other vocabularies.

Purpose

Because every drug information system that is commercially available today follows somewhat different naming conventions, a standardized nomenclature is needed for the smooth exchange of information, not only between organizations, but even within the same organization. For example, a hospital may use one system for ordering and another for inventory management. Still another system might be used to record dose adjustments or to check drug interactions. Several cooperating hospitals might have different systems, and find their data incomparable.

A standardized nomenclature that relates itself to terms from other sources can serve as a means for determining when names from different source vocabularies are synonymous (at an appropriate level of abstraction). The goal of RxNorm is to allow various systems using different drug nomenclatures to share data efficiently at the appropriate level of abstraction.

The Scope of RxNorm

RxNorm contains the names of prescription and many nonprescription formulations that exist in the United States.  However, some items may not be used in the United States.

RxNorm is intended to cover all prescription medications approved for human use in the United States. Prescription medications from other countries may be included as opportunities allow, a principal consideration being that there be an authoritative source of information about these drugs. Over-the-counter (OTC) medications will be added and covered, as well, when reliable information about the medications can be found. Medications, whether prescription or OTC, with more than three ingredients are not fully represented at the present time.

Additions to the vocabulary will be made as new products are put on the market (see Updates, below). Radiopharmaceuticals, because of the decay in strength over time and the requirement that they be ordered and prepared especially for a given time of administration, are listed only as ingredients.

The Elements of RxNorm

An RxNorm clinical drug name reflects the active ingredients, strengths, and dose form comprising that drug. When any of these elements vary, a new RxNorm drug name is created as a separate concept (explained below). Thus, an RxNorm name should exist for every strength and dose of every available combination of clinically significant ingredients.

Nonnumerical, named elements of the RxNorm clinical drug name are also individual RxNorm terms related by formal criteria to the clinical drug name.

II. RxNorm in Detail: Structure and Operation

How RxNorm is Structured

Connections, in the form of predefined relationships, exist among the components of RxNorm and, additionally, between RxNorm data and data derived from other vocabularies also contained in the UMLS Metathesaurus.

RxNorm data is distributed in Metathesaurus Relational (MR) or Rich Release Format (RRF) tables. The tables that will be of particular relevance in the following discussion are the following:

• RXNCONSO, Concept and Source Information
• RXNREL, Relationships
• RXNSAT, Attributes
• RXNSTY, Semantic Type

For detailed information about the fields, their formatting, and possible values or to learn about other UMLS tables, see the links in the following section.

Details of UMLS & RxNorm Structure

• Complete information on the structure of the UMLS system, its data elements, and its tables can be found in the UMLS Documentation, available online at http://www.nlm.nih.gov/research/umls/umlsdoc.html
• Information on the structure of individual tables may be found in Section 2.7 on File Format.
• Information on specific fields and the values they may take is in appendix 1.
• Abbreviations for the source vocabularies for strings found in the UMLS Metathesaurus and RxNorm may be found in appendix 2.
• Sample files showing table structure and sample field values are found at

  http://www.nlm.nih.gov/research/umls/mrsamples

  These samples may show updates to the file formats that are not yet reflected in UMLS Knowledge Sources.

• In part because of their different schedules of updates, RxNorm file structure differs in some ways from that of the UMLS. Details on the relation between RxNorm and UMLS files may be found at

  http://www.nlm.nih.gov/research/umls/rxnorm/docs/index.html

• The RxNorm Navigator (RxNav) is an interactive graph built on the model of the figure in the section on RxNorm Relationships below. It allows you to query the RxNorm database by any of its components (see the section immediately below). RxNav can be found at

  http://mor.nlm.nih.gov/download/rxnav

RxNorm follows a standard format in the naming of clinical drugs. Drugs named in disparate ways in various other vocabularies are linked to a normalized name prepared according to RxNorm’s naming conventions.

The normalized form of the name of a clinical drug may be thought of as being composed of a number of elements, each a concept in its own right. Each element of the normalized form can be identified by the value of the TTY [Term Type] field of RXNCONSO. The possible values are as follows:

IN                                Ingredient
(A compound or moiety that gives the drug its distinctive clinical properties. The preferred name is usually the USAN name.)
                                                                        Examples: Fluoxetine
                                                                       Insulin, Isophane, Human
                                                                       Gentamicin Sulfate (USP)

PIN                              Precise Ingredient
(A specified form of the ingredient that may or may not be clinically active. Most precise ingredients are salt or isomer forms.)
                                                                        Example: Fluoxetine Hydrochloride

DF                               Dose Form
(See appendix 2 for a list of dose forms available in RxNorm.)
                                                                        Example: Oral Solution

SCDC              Semantic Clinical Drug Component
(Ingredient plus strength—see section on Rules and Conventions, below, for units of measurement and for rules pertaining to the calculation of strengths.)
                                                                        Example: Fluoxetine 4 MG/ML

SCDF              Semantic Clinical Drug Form
                                                                        (Ingredient plus dose form.)
                                                                        Example: Fluoxetine Oral Solution

SCD                Semantic Clinical Drug
                                                                        (Ingredient plus strength and dose form.)
                                                                        Example: Fluoxetine 4 MG/ML Oral Solution

BN                               Brand Name
(A proprietary name for a family of products containing a specific active ingredient.)
                                                                        Example: Prozac

SBDC              Semantic Branded Drug Component
                                                                        (Branded ingredient plus strength.)
                                                                        Example: Fluoxetine 4 MG/ML [Prozac]

SBDF              Semantic Branded Drug Form
                                                                        (Branded ingredient plus dose form.)
                                                                        Example: Fluoxetine Oral Solution [Prozac]

SBD                 Semantic Branded Drug
                                                                        (Ingredient, strength, and dose form plus brand name.)
                                                                        Example: Fluoxetine 4 MG/ML Oral Solution [Prozac]

SY                               Synonym of another TTY, given for clarity
                                                                        Example: Prozac 4 MG/ML Oral Solution

A term type not listed here is OCD (obsolete clinical drug). It is discussed below in the section on Obsolete Records.

A Concept Orientation: RxNorm’s Links to Other Vocabularies

Like the UMLS Metathesaurus as a whole, RxNorm is organized by concept. A concept is a collection of names identical in meaning at a specified level of abstraction. It serves as a means whereby strings of characters from disparate sources may be taken to name things that are the same.

For example, Accuneb, 0.042% inhalation solution and Albuterol 0.417 MG/ML Inhalant Solution [Accuneb] name the same concept. In RxNorm, where a normalized form exists, it is designated as the preferred form of the name (by means of its association with the TS [Term Status] field in RXNCONSO). The concept is assigned an RxNorm concept unique identifier (RXCUI) of 575803. This RXCUI always designates the same concept, no matter the form of the name and no matter in what table it is found. Drugs whose names map to the same RXCUI are taken to be the same drug—identical as to ingredients, strengths, and dose forms. Conversely, drugs that differ in any of these particulars are conceptually distinct and will have different RXCUIs.

Acetaminophen 500 MG Oral Tablet and Acetaminophen 500 MG Oral Tablet [Tylenol], on the other hand, name two different concepts, with RXCUIs 198440 and 209459, respectively. The first of these bears the relationship “has_tradename” to the second, and the second bears the reciprocal relationship “tradename_of” to the first.

Similarly, two drugs, identical in their generic components, may still refer to different concepts if they differ in brand name. For instance,

Fluoxetine 20 MG Oral Capsule [Prozac] and
Fluoxetine 20 MG Oral Capsule [Sarafem].

RxNorm Relationships

Relationships between concepts in RxNorm are reciprocal. Each direction of the relationship is represented as a separate row in RXNREL. A clinical drug consists of components, and the components constitute the clinical drug. That is to say, a concept with a TTY field value of SCD bears the relationship “consists_of” to certain other concepts with a TTY value of SCDC, and each of these, in turn, bears the relationship “constitutes” to the first concept. This is shown graphically in the figure below.

For an interactive version of the diagram below, go to http://mor.nlm.nih.gov/download/rxnav/.

RxNorm Concepts and Relationships. RXCUI is the concept unique identifier. TTY is the term type. See the section of this document entitled “The Elements of Normalized Form” above for an explanation of the TTY values. Appendix 1 shows these relationships in tabular form.

These relationships are represented as follows in the data files: To use the example in the figure, the field RXCUI1 in the table RXNREL contains the value 315025, which the table RXNCONSO shows to be the RXCUI for Cetirizine 5 MG Oral Tablet, which has a TTY value of SCD. The field RXCUI2 in RXNREL has the value 328987, which is the RXCUI for Cetirizine 5 MG, and which has a TTY value of SCDC. The RELA field, which shows the relationship of RXCUI2 to RXCUI1, has the value “constitutes”. (See also appendix 1.)

When the values of RXCUI1 and RXCUI2 in RXNREL are interchanged, in the above example, the value of the RELA field will be “consists_of”. RxNorm contains the following relationships:

constitutes / consists_of

These relationships obtain between an SCD and an SCDC and between an SBD and an SBDC or SCDC.

contains / contained_in

These relationships hold between concepts naming clinical drugs and those naming the devices that dispense them (the latter being those concepts that have an STY [Semantic Type] field value of “Drug Delivery Device” in the table RXNSTY).

dose_form_of / has_dose_form

These relationships obtain between a DF and an SCD, SCDF, SBD, or SBDF.

form_of / has_form

These relationships hold between a base ingredient and a precise ingredient, if there is one.

ingredient_of / has_ingredient

These relationships obtain between an IN and an SCDC or SCDF and between a BN and an SBDC, SBD, or SBDF.

isa / inverse_isa

These relationships hold between an SCD and an SCDF and between an SBD and an SBDF.

precise_ingredient_of / has_precise_ingredient
These relationships obtain between an SCDC and a precise ingredient to designate the relationship of the clinical drug to a (usually) nonclinically significant variant of the active ingredient.

tradename_of / has_tradename

These relationships hold between a BN and an IN, between an SBDC and an SCDC, between an SBD and an SCD, or between an SBDF and an SCDF.

Rules and Conventions Used to Generate the Data

Naming Conventions

The SCD—the semantic clinical drug, or normalized form of the generic drug name—contains the ingredient(s), the strength, and the dose form, in that order. The components and forms of an SCD—its SCDCs and SCDFs—contain the ingredient and strength and the ingredient and dose form, respectively. The SBD follows a similar convention, with the addition of the brand name in brackets at the end of the name.

The ingredients named in the SCD, SBD, etc., are the active ingredients. Thus, in the example shown in the figure above, Cetirizine is used as the ingredient name. Though Cetirizine and Cetirizine Dihydrochloride are separate concepts, the normalized form of the drug name does not include the precise ingredient name since, in this case, the difference is without clinical significance.

Similarly, RxNorm makes no distinction between amoxicillin trihydrate, amoxicillin monosodium salt, or amoxicillin potassium salt, because the differences among them are not clinically significant. When there are significant differences among components, as is the case with Penicillin G, Benzathine and Penicillin G, Procaine, the entire compound name (the PIN) is always included as the ingredient.

Branded Drugs

Distinct concepts are created in RxNorm for brands whose formulations (i.e., whose aggregates of ingredients) are distinct.

For example, Bactrim and Bactrim DS both contain sulfamethoxazole and trimethoprim (and in the same proportions relative to one another), the DS indicating only that one product is twice as strong as the other. Records for both products link to the same BN.

However, in the case of Claritin (loratadine) and Claritin D (loratadine with pseudoephedrine), the “D” indicates an additional ingredient. RxNorm, therefore, contains distinct BNs for both Claritin and Claritin D.

Strengths

The strengths are based on the ingredient specified. In most cases, the strength will be that of the active ingredient; in a few cases strengths are expressed in amounts of precise ingredient.  In cases where there is more than one active ingredient, there will be a strength associated with each ingredient, as in the SCD below:

Ascorbic Acid 100 MG / Calcium Carbonate 625 MG / Ferrous Fumarate 122 MG / Folic Acid 1 MG Oral Tablet

In this example, the SCD bears the relationship “consists_of” to each of the several ingredient-strength pairs (essentially SCDCs) separated by slashes.

Strengths are expressed to three significant digits. Thus, nearly equal strengths, which may be expressed differently in different drug vocabularies, are treated as being equivalent. That is, when drug names derived from different source vocabularies would be taken to express the same concept (i.e., to name the same substance), except for a discrepancy in the strengths, and if the strengths given, upon conversion to common units, are identical to three significant digits, RxNorm treats the names as equivalent and assigns the same RXCUI to each string.

In most cases, the active ingredient will be the IN. Some drugs, however, will contain a mixture of salts, each of which has a significant and different clinical action. For example, Adderall contains two ingredients, amphetamine and dextroamphetamine. There are six variants of these two ingredients. Four of these variants are clinically active. The RxNorm SCD names each of these salts, with its individual strength, separately and in alphabetical order.

Amphetamine Aspartate 1.25 MG / Amphetamine Sulfate 1.25 MG / Dextroamphetamine Saccharate 1.25 MG / Dextroamphetamine Sulfate 1.25 MG Extended Release Capsule

Units of Measurement

In RxNorm only a few units are used, in order to standardize the expressions of strength. Where strengths are expressed as ratios, the ratio is given with a denominator value of 1 of the appropriate units. Thus, 100 mg in 5 ml would be expressed as 20 mg/ml.

The following units of measurement are used in RxNorm:
MEQ
     Milliequivalent.
MG
     Milligram.
ML
     Milliliter.
MMOL
     Millimole.
UNT
     Unit.
%
     Used only with gases, otherwise percentages are converted into ratios.

The following unit appears only in ratios:

ACTUAT
     Actuation. Refers to a measured dose per activation of a dispensing devise; e.g., in an inhaler,
     the strength of the clinical drug is given by how much is dispensed with each actuation.

MEQ/MG
MEQ/ML
MG/ACTUAT
MG/MG
MG/ML
ML/ML
PNU/ML
UNT/MG
UNT/ML

Conversion of Units

In making the RxNorm forms, other expressions of units are converted into the RxNorm standards. The rules followed are

Standard conversion factors are used between metric units.

One liquid ounce is taken to be equivalent to 25 milliliters.

A grain is 65 milligrams.

If a variable amount of diluent can be used, the minimum amount is used in RxNorm to calculate the concentration that determines the strength. For example, in the case of a drug that can be dissolved in 3 to 5 ml of diluent, RxNorm would use 3 ml. For intravenous solutions, only the initial dilution is used to calculate the strength. For example, a vial containing 50 mg of a drug to be dissolved in 2 ml of water, then added to an IV solution, is expressed as having strength of 25 mg/ml.

Reformulated Drugs
Reformulated drugs are drugs whose ingredients have been changed by the manufacturing company but that continue to be identified by the original brand name. A new BN is created in RxNorm to designate the reformulation and provide the date of the change. Sample SBDs are shown below:

Dihydroxyaluminum Sodium Carbonate 334 MG [Rolaids] became
Calcium Carbonate 550 MG / Magnesium Hydroxide 110 MG [Rolaids Reformulated Aug 2006]

Synonym Use
Because they list the names and strengths of each component, SCDs and SBDs may sometimes grow to inordinate lengths. This will be true of multivitamins, for instance.

In such cases, synonyms (TTY=“SY”) will be created in RxNorm as more manageable forms of the name.

Strength Expressed as Precise Ingredient
If RxNorm receives a string from one of its source vocabularies with the strength expressed in terms of the precise ingredient, this will be noted as an attribute in RXNSAT.

Biphasic and Triphasic Drugs
Another special case is the treatment of what are often referred to in other systems as “biphasic” or “triphasic” drugs (often sequential oral contraceptives). Since “biphasic” and “triphasic” tablets are not entities, but represent names for drugs given sequentially, RxNorm treats these, not as unique classes of drugs, but as separate SCDs contained in a drug delivery device. Thus, for example,

Ethinyl Estradiol 0.035 MG / Norethindrone 0.5 MG Oral Tablet and
Ethinyl Estradiol 0.035 MG / Norethindrone 1 MG Oral Tablet

are distinct concepts in RxNorm. Both of these SCDs bear the relationship “contained_in” to the concept Ortho-Novum 7/7/7 21 Tablets. The latter, reciprocally, bears the relationship “contains” to each of them. The concept Ortho-Novum 7/7/7 21 Tablets has a semantic type (i.e., field STY in table RXNSTY) of “Drug Delivery Device”.

Drug Delivery Devices
A drug delivery device may contain a combination of clinical drugs intended to be taken together or in sequence, or it may be a device to ensure that a clinical drug is taken properly. The specifics of the representation of such devices in RxNorm are being worked out at the present time.

National Drug Code (NDC)

Conflicts
RxNorm currently obtains NDCs from the Veterans Health Administration (VHA), the Food and Drug Administration, and the Multum Lexicon. Occasionally conflicts arise among these sources. This may be because of a distinction not made between a branded drug and its generic equivalent or because of a difference in units of measurement (e.g., one source expresses a measurement in terms of weight, another in terms of ionic equivalents) or because of simple data entry error. Instances such as these furnish RxNorm with an important quality assurance opportunity. 

NDCs are listed as attributes asserted by the source vocabulary.  Additionally, RxNorm will assert, as an RxNorm attribute, what is believed to be the correct association with NDC codes. When conflicts arise between sources, other means of obtaining information about the drug may be used in order to determine the correct NDC.

Cascading
RxNorm attributes (in table RXNSAT) use NDCs to link a generic drug to various branded drugs. In the example below, NDC codes and RxNorm attributes are expressed in a simplified form.

The example shows three clinical drugs, each contained in two different branded products. The NDCs are attached as attributes to the generic drug name in RXNSAT. The record for the generic drug contains NDCs for the branded drugs. RxNorm thereby allows a user to trace connections that could be important in checking for duplicate prescriptions, for instance, or for ascertaining the fulfillment of a prescription.

Codes and CUIs

The values of the Code field (in RXNCONSO, for example) are taken from various source vocabularies and are used, in those sources, to identify particular items in the vocabularies.

At one time, RxNorm concepts had a code (used for internal processing) that was different from the RXCUI. Now, all concepts with a Source Abbreviation (SAB) field equal to “RxNorm” have RXCUIs identical to their codes.

The following list indicates the fields in the source vocabularies from which the Code is drawn.

For two other sources, the field from which the Code is taken is determined by the term type used in the source record.

The last two MMSL term types are loaded into RxNorm as “NoCode”.

Cardinality

When a BN has more than one IN, this is noted as an attribute of the BN, with the value “multi”, in table RXNSAT. To find those ingredients, the user should follow the relationship attribute RELA in the RXNREL table (see appendix 1, showing the values that RELA can take in relation to the term type BN).

Updates

All RxNorm files excett for RxNAtomArchive.rrf are included in the UMLS Metathesaurus. But while the Metathesaurus, as a whole, is updated quarterly, RxNorm is updated more frequently. Between releases of the UMLS, RxNorm update files are made available through the UMLS Knowledge Source Server. These files are consistent with the latest extant release of the UMLS, but will contain additional naming information available since that release.

It is important to note that the RxNorm files available include names and data from other sources, even though those names are not part of RxNorm. The availability of those names in the RxNorm subset should not be considered as an indication that these can be used without proper consideration of their UMLS licensing restrictions. The restrictions still apply. However, it seems advisable to make those names and relationships available in the updates, in order to support the maintenance of a current drug vocabulary.

Because RxNorm is updated so much more frequently than the rest of the UMLS, RxNorm maintains separate concept unique identifiers. At the time of a resynchronized release, every RxNorm RXCUI should have a one-to-one relationship with a UMLS CUI.

Obsolete Records

Obsolete records are marked in three ways, depending on the source of the record and its relationships with other records.

(1) When one of RxNorm’s source vocabularies drops a clinical drug name—that is, when the name had been used in a previous version of that source’s vocabulary but is not found in the most recent version—the old clinical drug records are given the term type OCD (for obsolete clinical drug) in RXNCONSO. The record is updated with RxNorm as the source (SAB field), but retains the original SAB, VSAB, TTY, and Code as attributes in RXNSAT. Any existing relationships to RxNorm records will be maintained.

(2) When a clinical drug disappears from the U.S. market, and therefore from the source vocaublaries, the RxNorm SCD should correspond only to OCDs; i.e., it will reside in the same concept exclusively with other records whose TTY fields contain the value OCD. At that time, it is flagged with an “O” (for Obsolete) in the Suppress field in RXNCONSO.

(3) If, during a resynchronization with the UMLS (see Updates, above), it is found that there is more than one RxNorm record in the same concept, then one of the records is marked as the preferred one and the others are archived. The archive file is called RXNATOMARCHIVE.

Downloading RxNorm

RxNorm files are available through the UMLS Knowledge Source Server

http://umlsks.nlm.nih.gov/kss/servlet/Turbine/template/admin,user,KSS_login.vm

and may be downloaded as zipped text files or extracted from the UMLS using the extraction subsetter, MetamorphoSys. Because of the difference in update frequency between RxNorm and the rest of the UMLS, the zip files will be the more current. Users may want to use MetamorphoSys, however, if they want information not included in RxNorm, such as drug class or structural or hierarchical information found in the UMLS.

          III. RxNorm in Use

Identification of Relationships
The following sample questions and algorithmic solutions illustrate the retrieval of RxNorm information using UMLS data tables.

In what follows, field labels are given in capital letters on the left side of the equals sign; field values are given within quotation marks; and field descriptive names, when provided for clarity, are given in square brackets.

Taking amoxicillin as exemplar throughout, we can first find all RxNorm concepts related to amoxicillin. In general, other algorithms than the ones shown here may also be available to achieve the same results.

1. In RXNCONSO

• Find any record with STR[String]=“amoxicillin”.
• Retrieve RXCUI [Concept Unique Identifier].
• NOTE: All strings containing only the word “amoxicillin” will map to the same concept, regardless of capitalization or source vocabulary. That concept, expressed by the RXCUI, will have TTY[Term Type]=“IN” when SAB[Source Abbreviation]=“RXNORM”.

2. In RXNREL

• Using the RXCUI retrieved from step 1 as the value of RXCUI1, find any record(s) with RELA[Relationship Attribute]=“form_of”.
• NOTE: RELA is the relationship of RXCUI2 to RXCUI1.
• Retrieve RXCUI2.
• NOTE: This step is not strictly necessary in the case of amoxicillin. Its purpose is to retrieve any variants of the active ingredient that might affect the form of the SCD, SCDC, SCDF, SBD, SBDC, or SBDF; i.e., any variants that might be clinically significant. (See discussion above under Rules and Conventions: Naming Conventions.)

3. Let {Ω} stand for the set containing all the RXCUIs retrieved in steps 1 and 2.

Q. What trade names is amoxicillin sold under?

In RXNREL

• Taking RXCUI1={Ω}, retrieve the RXCUI2 value for all records with RELA=“tradename_of”.

In RXNCONSO

• Using the retrieved value as the RXCUI in RXNCONSO, find all records with SAB=“RXNORM”.
• Retrieve STR.
• NOTE: This retrieves the normalized form of all amoxicillin concepts with TTY= “BN”.

Q. What strengths of amoxicillin are available?

In RXNREL

• Taking RXCUI1={Ω}, retrieve the RXCUI2 value for all records with RELA=“has_ingredient”.

In RXNCONSO

• Using the retrieved value as the RXCUI in RXNCONSO, find the records with TTY=“SCDC” for which SAB=“RXNORM”.
• Retrieve STR.

Q. What dose forms of amoxicillin are available?

In RXNREL

• Taking RXCUI1={Ω}, retrieve the RXCUI2 value for all records with RELA=“has_ingredient”.

In RXNCONSO

• Using the retrieved value as the RXCUI in RXNCONSO, find the records with TTY=“SCDF” for which SAB=“RXNORM”.
• Retrieve STR.

Q. What is the National Drug Data File (NDDF) code for amoxicillin?

In RXNCONSO

• Using the RXCUI retrieved from step 1 as the value of RXCUI1 and SAB=“NDDF,” find the value of the field CODE.

Q. Given the NDDF code, how can I find the code for SNOMED, Version 3.5?

In RXNCONSO

• Search for a record having SAB=“NDDF” and the given value for the CODE field.
• Retrieve RXCUI.
• Find a record having that RXCUI and SAB=“SNMI” (abbreviation for SNOMED International from UMLS Knowledge Sources, appendix 2. See the section on Details of UMLS and RxNorm Structures above).
• Retrieve CODE.

Use in Electronic Prescribing and Computerized Order Entry
The representation of the relationships between names of drugs from various drug information sources, their ingredients, strengths, and dose forms should provide a necessary structure for support of electronic prescription writing and physician order entry. However, in some instances, this set of relationships may not be sufficient to convey all of the desired attributes of an order. Some inactive ingredients may still be of interest; e.g., lactose, dextrose, alcohol, flavorings, or dyes. Where packaging of products may be of particular interest (e.g., dose packs), the link between the drug delivery device and the RxNorm form will present the necessary information. In other cases (e.g., vial size or the making up of intravenous solutions), the person preparing the solution will be obligated to review the material at hand, and choose appropriately.

Radiopharmaceuticals create a special case. Since they must be specially ordered to have the appropriate radioactivity at a given time, they will not be represented except as a range of approximate activities.

Appendix 1
RxNorm Relationship Mappings

Appendix 2
RxNorm Dose Forms with Definitions

Only forms whose names are given in bold are used. Additional terms for the same form (not necessarily synonymous, and in some cases ambiguous) are listed in parentheses after the term. Some additional hierarchical nodes are given to aid in finding the correct form.