The RxClass Browser is a web application for exploring and navigating through the class hierarchies to find the RxNorm drug members associated with each class.

The RxClass API is available for users to include RxClass data in their applications.

RxClass links drug classes with several drug sources to their RxNorm drug members (usually ingredients, precise ingredients and multiple ingredients).

RxClass allows users to search by class name or identifier to find the RxNorm drug members or, conversely, search by RxNorm drug name or identifier to find the classes that the RxNorm drug is a member of.

Note: In June 2018, NDF-RT was replaced by MED-RT as a source of drug class relations. Additionally, the VA drug-class relations contained in NDF-RT were replaced by VANDF data.

Class Types

RxClass contains ten drug class trees:

• ATC1-4 - Anatomical Therapeutic Chemical (ATC) containing class levels 1 through 4. The ATC classification system divides the drugs into different groups according to the organ or system on which they act and according to their chemical, pharmacological and therapeutic properties. The drugs are divided into 14 main groups (first level), with two therapeutic/pharmacological subgroups (second and third levels). The fourth level is a therapeutic/pharmacological/chemical subgroup and the fifth level is the chemical substance. The second, third and fourth levels are often used to identify pharmacological subgroups when these are considered to be more appropriate than therapeutic or chemical subgroups.
• MeSHPA - Medical Subject Headings (MeSH) pharmacological actions. In MeSH, every drug and chemical MeSH heading has been assigned one or more headings that describe its pharmacological action (PA).
• EPC - FDA Established Pharmacologic Classes. In support of the FDA Structured Product Labeling (SPL) initiative, a hierarchy of FDA Established Pharmacologic Class (EPC) concepts is contained in MED-RT.
• Chem - Chemical structure and classification containing chemicals or other drug ingredients, organized into a chemical structure classification hierarchy, from NLM’s MeSH with slight modifications, beneath the “Substances and Cells” concept.
• Disease - Disease classification containing pathophysiologic as well as certain non-disease physiologic states that are treated, prevented, or diagnosed by an ingredient or drug product. May also be used to describe contraindications. These concepts are organized into a classification hierarchy from NLM’s MeSH (Medical Subject Headings), beneath the “Diseases, Life Phases and Physiologic States” concept.
• MoA - Mechanism of Action in MED-RT, containing molecular, subcellular, or cellular effects of drug generic ingredients, organized into a chemical function classification hierarchy, beneath the “Cellular or Molecular Interactions” concept.
• PE - Physiologic Effects in MED-RT, containing tissue, organ, or organ system effects of drug generic ingredients, organized into an organ system classification hierarchy, beneath the “Physiological Effects” concept.
• PK - Pharmacokinetics in MED-RT, containing collections of concepts describing the absorption, distribution, and elimination of drug active ingredients, beneath the “Clinical Kinetics” concept.
• VA - VA drug classes from VANDF, whose members are clinical drugs.
• TC - Therapeutic Categories from MED-RT, a small, experimental collection of general therapeutic intents of drug generic ingredients, organized into an organ system-oriented classification hierarchy, beneath the “Therapeutic Categories [TC]” concept.

Sources of Drug-Class Relations

There are seven sources which associate generic drugs to the classes listed above.

• ATC (level 5). The fifth level of the ATC tree contains the drugs.
• MeSH. MeSH drugs are associated with the pharmacological actions.
• VA. The VA drugs are associated with the VA classes.
• DailyMed. The DailyMed API maps substances through their UNII Code values to EPC, Chem, MoA and PE classes.
• MEDRT. Drug concepts in MED-RT are associated to Disease, MoA, Chem, PE, and PK classes.
• FDASPL. The FDASPL drug source maps drug concepts in MED-RT to EPC, Chem, MoA and PE classes.
• FMTSME. The FMTSME drug source maps drug concepts in MED-RT to TC classes.

Note: the three sources - DailyMed, MEDRT and FDASPL - contain overlapping and redundant associations of drugs to some of the class trees (see tables below), so to avoid confusion only one of those sources is selected at any given time in RxClass.

The following table lists the drug sources and the classes they associate with .

Class \ Source	ATC	MeSH	DailyMed	FDASPL	FMTSME	MEDRT	VA
ATC1-4	X
MeSHPA		X
EPC			X	X
Chem			X	X		X
Disease						X
MoA			X	X		X
PE			X	X		X
PK						X
TC					X
VA							X

Relationships to Drug Classes

The following table shows the relationships each drug source uses to identify with the drug class.

Drug Source	Relation	Drug Class	Description
ATC (level 5)		ATC1-4	Drug members of an ATC class
MeSH		MeshPA	Drug members of a MeSH Pharmacologic Action
DailyMed	has_EPC	EPC	Drug members of a FDA Established Pharmacologic Class
DailyMed	has_Chemical_Structure	Chem	Drugs that have a chemical structure
DailyMed	has_MoA	MoA	Drugs that have a Mechanism of Action
DailyMed	has_PE	PE	Drugs that have a Physiologic Effect
FDASPL	has_EPC	EPC	Drug members of a FDA Established Pharmacologic Class
FDASPL	has_Chemical_Structure	Chem	Drugs that have a chemical structure
FDASPL	has_MoA	MoA	Drugs that have a Mechanism of Action
FDASPL	has_PE	PE	Drugs that have a Physiologic Effect
FMTSME	has_TC	TC	Drugs that have Therapeutic Categories
MEDRT	CI_ChemClass	Chem	Drugs that are contraindicated with a chemical class
MEDRT	has_ingredient	Chem	Drugs that are members of a chemical class
MEDRT	has_active_metabolites	Chem	Drugs that have active metabolites in a chemical class
MEDRT	CI_with	Disease	Drugs that are contraindicated with a disease
MEDRT	induces	Disease	Drugs that induce a disease
MEDRT	may_diagnose	Disease	Drugs that may diagnose a disease
MEDRT	may_prevent	Disease	Drugs that may prevent a disease
MEDRT	may_treat	Disease	Drugs that may treat a disease
MEDRT	CI_MoA	MoA	Drugs that are contraindicated with a Mechanism of Action
MEDRT	has_MoA	MoA	Drugs that have a Mechanism of Action
MEDRT	CI_PE	PE	Drugs that are contraindicated with a Physologic Effect
MEDRT	has_PE	PE	Drugs that have a Physiologic Effect
MEDRT	has_PK	PK	Drugs that are members of a Pharmacokinetics Class
MEDRT	site_of_metabolism	PK	Drugs that have a site of metabolism in a Pharmacokinetics Class
VA	has_VAClass	VA	Clinical drugs that are members of a VA Class
VA	has_VAClass_extended	VA	Clinical drugs that are derived members of a VA Class

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