AHFS Pharmacologic-Therapeutic Classification

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The AHFS Pharmacologic-Therapeutic Classification was developed and is maintained by ASHP. Originally published by ASHP in the inaugural edition of the American Hospital Formulary Service (AHFS; now AHFS Drug Information), the Classification has been the foundation for organizing drug formularies in institutional, governmental, and other settings since 1959. The AHFS Pharmacologic-Therapeutic classification originated as an adaptation of the drug classification used to organize the University of Michigan’s Hospital Formulary of Selected Drugs. The principal change reflected in the 1959 adaptation was the incorporation of a hierarchical numeric structure to the alpha description of the drug classes and subclasses. The AHFS classification allows the grouping of drugs with similar pharmacologic, therapeutic, and/or chemical characteristics in a 4-tier hierarchy. There are 31 classifications in the first tier, 189 in the second tier, 269 in the third tier, and 105 in the fourth tier.

It has been included in the International Classification of Diseases (ICD) and employed by US state Medicaid programs and by Health Canada for several decades. In the current versions of ICD-9-CM and ICD-10-CM, the AHFS Classification is assigned equivalent diagnosis codes for coding adverse effects and poisonings by drugs. State Medicaid programs in the US have employed the Classification to organize their drug formularies and to facilitate utilization review of drugs by class. Health Canada and the provincial governments have employed the Classification for similar purposes.

In the US, the state of Vermont adopted the AHFS Pharmacologic-Therapeutic Classification as the basis for physicians and other prescribers to compare prices for similar drugs under the conditions of the state’s Pharmaceutical Marketer Price Disclosure Law (33 V.S.A. § 2005a; effective March 1, 2005).

The US Centers for Medicare & Medicaid Services (CMS), in 2005, adopted the AHFS Pharmacologic-Therapeutic Classification as the only named alternative to the USP Model Guidelines for use by Prescription Drugs Plans (PDPs) in the drug formularies they develop to implement the outpatient prescription drug benefit (i.e., Part D) in the Medicare Modernization Act (MMA) of 2003. This program went into effect January 2006.

Effective June 6, 2005, the AHFS Pharmacologic-Therapeutic Classification became a registered vocabulary in the HL7 OID registry (OID: 2.16.840.1.113883.6.234).

In November, 2009, NCPDP accepted the AHFS Pharmacologic-Therapeutic Classification system as an element in the SCRIPT (e-Prescribing) and Telecom (telecommunications of medication information) standards as well as on the External Code List.

The AHFS Pharmacologic-Therapeutic Classification also is included in the data structure of major pharmacy information database and systems vendors (e.g., First Databank, Lexicomp, Medispan, Micromedex (Truven), McKesson, Health Information Designs, Affiliated Computer Systems, EDS) for a variety of applications.

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 classification system has been in use in hospitals and health-systems for over 50 years as a logical way to group drugs for easy comparison during P&T Committees as well as aggregate reporting on drugs for utilization and billing.

The classification is available by itself or also with companion mapping tables to the US National Drug Code (NDC) and RxNorm identifiers.

This product is available in delimited ASCII file format for easy import into a relational database.

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.

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

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 Classification 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.

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
         28:08.04.24 Salicylates

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):

  1. 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
  2. Colesevelam
    • 24:06.04 – Cardiovascular Drugs » Antilipemic Agents » Bile Acid Sequestrants
    • 68:20.92 – Hormones and Synthetic Substitutes » Antidiabetic Agents » Miscellaneous Antidiabetic Agents
  3. 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
  4. Breo Ellipta® (fluticasone/vilanterol)
    • 68:04 – Hormones and Synthetic Substitutes » Adrenals
    • 12:12.08.12 – Autonomic Drugs » Sympathomimetic (Adrenergic) Agents » β-Adrenergic Agonists » Selective β2-Adrenergic Agonists

Primary Data Tables

  1. 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

     

  2. 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

     

  3. 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

The AHFS Pharmacologic-Therapeutic Classification System can be licensed from ASHP and 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 ASHP is prohibited.

Drug Assignments and Reassignments.

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