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Medication
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Introduction

The standardization of drugs is still evolving. Since technology is rapidly changing the structure and types of drugs, the classification system will continue to under go refinement.

Classifications are based on:

• Mechanism of action
• Physiologic effects (cellular or molecular interactions)
• Clinical Drug (Active Ingredients)
• Therapeutic Intent (Conditions treated)

Other Features to consider

• Generic Names

• Trade Names

• Dosage Forms

• Strength

• Package size

• Package type

• Manufacturer

• UMLS CUI

• MeSH definitons

Definitions

A clinical drug is defined as one or more active ingredients, prepared in a particular dose form at a particular strength. It is sometimes referred to as a drug product.

The mechanism of action of a drug is how it functions physiologically at the cellular or subcellular level, and therapeutic intent is why a drug is used for a patient.

Therapeutic intent is the umbrella under which on- and off-label uses would be classified.

Discussion

Many existing classifications systems were are still based on old drugs and their therapeutic approaches and many of the new drugs may routinely be classified as "other". New "designer" drugs are pushing the classification systems into new dimensions. New classifications that address current disease issues are also added to some classification systems. Examples of these are Anti-HIV and Antineoplastics Agents

Drugs today are also more often being used together in "cocktails" or in adjunctive therapy in combination. These cocktails are used synergistically to provide a wide range of physiological responses. 

And...there are a number of drugs for which the mechanism of action is not known.

Existing Systems

There are several competing systems

• British National Formulary (BNF)

• FirstDataBank

• Model Guideline (Medicare Prescription Drug Benefit)

• National Drug Coding (NDC) system

• National Drug File - Reference Terminology (NDF-RT model) based on the VHA system

• SNOMED-CT has developed standards for Dosage Form and Unit of Measurements.

• Master Drug Data Base (MediSpan^TM)  

• Multum

• Micromedex

• NDF-RT National Drug File Reference Terminology. The National Drug File, Reference Terminology is being developed for the Veterans Administration as a reference standard for medications to support a variety of clinical, administrative and analytical purposes.

• RxNorm RxNorm provides standard names for clinical drugs (active ingredient + strength + dose form) and for dose forms as administered to a patient. It provides links from clinical drugs, both branded and generic, to their active ingredients, drug components (active ingredient + strength), and related brand names. NDCs (National Drug Codes) for specific drug products (where there are often many NDC codes for a single product) are linked to that product in RxNorm. RxNorm links its names to many of the drug vocabularies commonly used in pharmacy management and drug interaction software, including those of First Databank, Micromedex, MediSpan, and Multum. By providing links between these vocabularies, RxNorm can mediate messages between systems not using the same software and vocabulary

WHO

WHO - Model Guideline

The Model guideline of Medicare is the newest classification proposed as of December 2004. This system will more than likely be "The System" used in the US

1. Technical Report Series 895 (2000)

The current Essential Drug List is arranged in 27 sections and is further subdivided into 76 second level subsections, 23 third and four 4th level subsections.

The Technical Report Series (TRS) Structure has been used in:

• AFRO Essential Drugs Price Indicator 

• ECHO, International Health Services Ltd (UK)

• International Dispensary Association (Netherlands) 

• International Drug Price Indicator Guide (MSH/WHO)

• National Essential Drug Lists may follow exactly the TRS section system, may use it with slight modification or use an entirely different system. 

• New Emergency Health Kit (1998).

• UN Emergency Relief Items, Volume 2, Compendium of basic specifications

• UNICEF Supply Division

2. Secretariat Proposal (2002)

A new arrangement is a proposed using 32 clinical grouping without other levels, subgroups or subsections.

3. Anatomical, Therapeutic, Chemical (ATC)

Introduction

Structure of ATC

The classification categorises substances at five different levels according to the organ or system on which they act and their chemical, pharmacological and therapeutic properties. There are fourteen main groups (1^st level), with one pharmacological/therapeutic subgroup (2^nd level). The 3^rd and 4^th levels are chemical/pharmacological/therapeutic subgroups and the 5^th level represents the chemical substance. The use of anatomical, therapeutic and pharmacological levels is, however, not strictly organised. Table 1 shows the first level ATC categories.

Table 1 Main groups of the Anatomical Therapeutic Chemical classification

ATC codes are alphanumerical and use 7 positions. The character in the 4^th position makes it possible to distinguish an ATC code from an ICD-10 code. ICD-10 never uses alphabetic characters in this position but ATC always does. An example of the code structure is given in Table 2.

Table 2 Example of ATC code structure (metformin)

Medicinal products are primarily classified according to the main therapeutic use of the main active ingredient. The basic principle is one ATC code for each pharmaceutical formulation (i.e. similar ingredients, strength and pharmaceutical form). A substance can be given more than one ATC code if it is available in two or more strengths or formulations with clearly different therapeutic uses. It is important to note that a medicinal product may be used for more than one equally important indication and the main therapeutic use of a drug may differ between countries. In these situations there are often several classification alternatives. Problems such as these are discussed in the WHO International Working Group for Drug Statistics Methodology where the final classification is decided. The principles of classification are further described in the guidelines to ATC classification (1)

The ATC classification has been developed by the WHO Collaborating Centre for Drug Statistics in Oslo, Norway. The full system classifies drugs into groups at five different levels resulting in some cases in a 7 digit/letter code. There are 14 first level groups and 99 second level groups. The example given uses only the first and second levels. Essential drugs fall into 66 groups.

4. WHO Model Formulary 

The WHO Model Formulary uses the same system of sections as the Technical Report series, sometimes named differently. There is more extensive use of subsections and there is much cross referencing in the text.

Secretariat recommendation

The Secretariat is inclined to favour some form of example 2 recognizing that all systems have advantages and disadvantages.

Advantages and disadvantages of three possible EDL structures (1, 2 and 3)

1) Technical Report Series sections

2) Secretariat proposal

3) ATC classification sections

National Drug Coding (NDC) system

In the US reporting systems generally use the NDC system. The NDCs are unique 11-digit codes that identify discrete drug products. The first five digits refer to the manufacturer. The next four digits correspond to the drug product. The last two digits indicate the packaging. Consequently, the NDCs are commercially- oriented and do not contain any mechanism to group drugs according to ingredients or categories of ingredients. 

NDF-RF

The core of the NDF-RT model comes from the existing VHA database file. The VHA drug classes (approximately 400) are similar to the categories and classes in the Model Guidelines, First Data Bank, Medispan, and Micromedex classification systems. NDF-RT differs from the existing systems in that drugs may appear in multiple classes, e.g., a drug can be classified as both an antihypertensive and a beta-blocker. The classes are legacy classes developed by the VA informed by the FDA-approved labeling but are not directly based on the specific language of the label. Indication is separated from the physiologic effect of the drug. The chemical structure of the drug molecule also is separated out.

Master Drug Data Base (MediSpan^TM)  

The MediSpan system contains complete records for prescriptions common in retail pharmacy as well as unit-dose and injectables used by hospitals and external facilites. MediSpan now includes over 100,000 generic drug products, products from regional manufacturers, and information on over 90,000 inactive drugs. The hierarchical identifier, the Generic Product Identifier (GPI) contained in MediSpan, is a 14-character field consisting of seven subsets, each providing increasingly more specific information about the drug (each using two of the 14-character field.

• Drug Group (Major Grouping)
• Drug Class
• Drug sub-class
• Drug name
• Drug name extension (generally the salt of the drug name)
• Dosage form

 Links

• Medicare Prescription Drug Benefit Model Guidelines Final Report (pdf)

• WHO Collaborating Centre for Drug Statistics Methodology

• First Data Bank
• Micromedex classification systems.

• MediSpan  Master Drug Database

• HL7 Dosage Form Standards

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