AHFS Pharmacologic-Therapeutic Classification System

The Order of Data

The AHFS Pharmacologic-Therapeutic Classification has been in use in hospitals in the United States since its inception in 1959. An integral part of the American Hospital Formulary Service, the AHFS classification allows the grouping of drugs with similar pharmacologic, therapeutic, and/or chemical characteristics in a 4-tier hierarchy. There are 30 primary classifications, 183 secondary classifications, 252 tertiary classifications, and 88 quaternary classifications represented by coding and a text description. Today, the AHFS classification is used by many people outside of hospitals.

It is used by ICD (International Classification of Diseases) for grouping adverse events for drugs, by state Medicaid and insurance companies for DUR (Drug Utilization Review), and by Health Canada and the provincial governments to organize their drug formularies and to facilitate utilization review of drugs by class.

It is the only named alternative to USP's Model Guidelines for use by prescription drug plans in implementing the formulary portion of the outpatient prescription drug benefit (i.e., Part D) in the Medicare Modernization Act (MMA) of 2003.

An environmental scan of formulary structures and drug classification systems conducted by Booz Allen Hamilton revealed the widespread use of the AHFS classification system, stating that it is a "recognized standard for systemic classification of drugs that uses a coding system to organize drugs" and that it is "a key reference and starting point for formulary development because it is readily available and universally accepted by physicians."

The AHFS Classification is a registered external code system in the HL7 Vocabulary Repository. (OID: 2.16.840.1.113883.6.234).

First Tier Classifications

The following table lists the first tier in the Classification. All marketed drug products fall under one or more of these classifications:

AHFS Class Number	AHFS Class Description
4:00	Antihistamine Drugs
8:00	Anti-infective Agents
10:00	Antineoplastic Agents
12:00	Autonomic Drugs
16:00	Blood Derivatives
20:00	Blood Formation, Coagulation, and Thrombosis Agents
24:00	Cardiovascular Drugs
28:00	Central Nervous System Agents
32:00	Contraceptives (foams, devices)
34:00	Dental Agents
36:00	Diagnostic Agents
38:00	Disinfectants (for agents used on objects other than skin)
40:00	Electrolytic, Caloric, and Water Balance
44:00	Enzymes
48:00	Respiratory Tract Agents
52:00	Eye, Ear, Nose, and Throat (EENT) Preparations
56:00	Gastrointestinal Drugs
60:00	Gold Compounds
64:00	Heavy Metal Antagonists
68:00	Hormones and Synthetic Substitutes
72:00	Local Anesthetics
76:00	Oxytocics
78:00	Radioactive Agents
80:00	Serums, Toxoids, and Vaccines
84:00	Skin and Mucous Membrane Agents
86:00	Smooth Muscle Relaxants
88:00	Vitamins
92:00	Miscellaneous Therapeutic Agents
94:00	Devices
96:00	Pharmaceutical Aids

Explanation of Devices and Pharmaceutical Aids

The AHFS Pharmacologic-Therapeutic Classification System includes components that would normally fall outside the scope of AHFS Drug Information but need to be included as a placeholder for specific customers' needs.

Most medical devices can be classified by finding the matching description of the device in Title 21 of the Code of Federal Regulations (CFR), Parts 862-892. FDA has classified and described over 1,700 distinct types of devices and organized them in the CFR into 16 medical specialty "panels" such as Cardiovascular devices or Ear, Nose, and Throat devices. These panels are found in Parts 862 through 892 in the CFR. For each of the devices classified by the FDA the CFR gives a general description including the intended use, the class to which the device belongs (i.e., Class I, II, or III), and information about marketing requirements. Subdivision of the 94:00 classification directly follows the FDA's Device Classifcation Panels.

A list of pharmaceutical aids, also referred to as excipients, is found in the USP-NF (United States Pharmacopeia-National Formulary). In general, they are substances having slight or no value therapeutically, but are used in the preparation of various pharmaceuticals, including preservatives, solvents, ointment bases, and flavoring, coloring, diluting, emulsifying, and suspending agents.

Sample Expansion to the Fourth Tier

Some classes, like 16:00 and 60:00, only have a first tier, but others continue down the hierarchy with more granularity the further they go.

Compare the class for celecoxib (28:08.04.08) with aspirin (28:08.04.24):

AHFS Class Number	AHFS Class Description
28:00.00.00	Central Nervous System Agents
28:08.00.00	Analgesics and Antipyretics
28:08.04.00	Nonsteroidal Anti-inflammatory Agents
28:08.04.08	Cyclooxygenase-2 (COX-2) Inhibitors
28:08.08.24	Salicylates

Multiple Classes per Drug

Because of the structure of the Classification system, there are several cases where a drug can have multiple classes, either by indication, mechanism of action, or route of administration. All classes for a drug are considered equally valid, however, due to space constraints for the printed edition of AHFS Drug Information (organized by AHFS Classification), it is necessary for us to make a choice as to which classification the monograph will be printed under. All other valid classes will have a cross-reference to the "print class."

Because the AHFS Classification is assigned to the active ingredient, combination products inherit all of the classifications of the individual ingredients.

Examples of Multiple Classes (the most granular classification codes are listed with a text description of all relevant classes in the hierarchy):

Labetalol

24:04.04.16 - Cardiovascular Drugs » Cardiac Drugs » Antiarrhythmic Agents » Class II Antiarrhythmics
24:08.04 - Cardiovascular Drugs » Hypotensive Agents » α-Adrenergic Blocking Agents
24:08.08 - Cardiovascular Drugs » Hypotensive Agents » β-Adrenergic Blocking Agents
24:24 - Cardiovascular Drugs » β-Adrenergic Blocking Agents

Colesevelam

24:06.04 - Cardiovascular Drugs » Antilipemic Agents » Bile Acid Sequestrants
68:20.92 - Hormones and Synthetic Substitutes » Antidiabetic Agents » Miscellaneous Antidiabetic Agents

Gentamicin

8:12.02 - Anti-infective Agents » Antibacterials » Aminoglycosides
52:04.04 - Eye, Ear, Nose, and Throat (EENT) Preparations » Anti-infectives » Antibacterials
84:04.04 - Skin and Mucous Membrane Agents » Anti-infectives » Antibacterials

Structure of the Classification Database

Primary Data Tables

tblAHFSClass: table defining the classification and its hierarchical structure

AHFSClassID: a permanent, unique numeric identifier that represents a specific therapeutic class
AHFSClassNum: The classic AHFS Pharmacologic-Therapeutic Classification (PTC) number
AHFSClass6: The legacy AHFS PTC number represented without punctuation dividers as a 6-digit code (DO NOT use this class; it is being provided solely for legacy systems in the process of updating to AHFS8)
AHFSClass8: The classic AHFS PTC number represented without the punctuation dividers as an 8-digit code
AHFSClassText: The official AHFS PTC description (name) (may not be unique)
AHFSClassTextShort: An abbreviated version of the official description (may not be unique)
AHFSClassTextLong: The long version of the official description (unique)
AHFSClassTextConsumer: The consumerized version of the AHFS classification (Diuretics = Water Pills)
AHFSClassParentID: Identifies the classification that is one level higher in the hierarchy from this classification ("0" if this class is a root class)
AHFSClassHasSubclass: Indicates that this class has subclasses (0 "no" or 1 "yes")
AHFSRootParentID: Identifies the classification that is at the root level of the hierarchy from this classification ("0" if this class is the root class)
AHFSSeqNum: Indicates the sort order for classes on the same level of the hierarchy with the same parent class
AHFSHierarchyLevel: Indicates what level in the hiearchy this class belongs (currently there are only 4 levels of hierarchy)
AHFSPrint: Indicates whether this class is currently in use in the print version of AHFS (0 "no" or 1 "yes")
AHFSPrintOrder: A non-permanent, unique number that represents the order in which the classes are displayed in print
AHFSRetired: Indicates that this classification has been retired (0 "no" or 1 "yes")
AHFSRetiredDate: Provides the date when this class was retired (YYYYMMDD)
AHFSAddDate: Provides the date when this class was first introduced into the classification (YYYYMMDD)
AHFSCxDate: Provides the date when this class was last modified (YYYYMMDD)
AHFSCxDesc: A text description of the change that occurred on the last modified date

tblAHFSDrugs: table associating the AHFS Classification with corresponding AHFS Drug Information monographs by generic name

GenDrugName: This corresponds to the short title of an AHFS monograph
UN: This number corresponds to the ID number of the AHFS monograph
AHFSClassID: This refers to the primary key AHFSClassID found in tblAHFSClass
PrintClass: This flag indicates whether the associated monograph in this record is printed under this classification in the AHFS Drug Information book or if this is a secondary classification for this drug monograph

tblAHFSTradenames: table associating generic drug names, tradenames, and synonyms with corresponding AHFS Drug Information monographs

UN: This number corresponds to the ID number of the AHFS monograph
ShortTitle: The short title from the AHFS monograph
Tradename: Any drug term found in AHFS for this monograph
Type: GN = Generic Name; TN = Trade Name; SYN = Synonym

Secondary Data Tables

Additional mapping tables are available to relate AHFS Classification codes to NDC and/or RxNorm

Availability

The AHFS Pharmacologic-Therapeutic Classification System may be licensed from the American Society of Health-System Pharmacists. A fee for commercial use may apply. Changes to the classification system are published each year coinciding with the release of each annual edition of the printed AHFS Drug Information. Intermediate updates may also be published throughout the year.

All material distributed as part of AHFS Drug Information is copyrighted. Reproduction, storage on a retrieval system, or transmission of this material or any part thereof in any form or by any means without the express written permission of the American Society of Health-System Pharmacists is prohibited.

Please contact ASHP at +1 (301) 664-8764 or by email at marketing@ashp.org for more detailed information.

Search