Development of a Compendial Taxonomy and Glossary for Pharmaceutical Dosage Forms
Keith Marshall, Chair, USP Pharmaceutical Dosage Forms Expert Committee; Thomas S. Foster, Chair, USP Biopharmaceutics Expert Committee; Herbert S. Carlin, Chair, USP Nomenclature and Labeling Expert Committee; and Roger L. Williams, EVP & CEO, United States Pharmacopeia
ABSTRACT Members of the Pharmaceutical Dosage Forms Expert Committee (PDF EC) began development of this pharmaceutical dosage form taxonomy scheme and related glossary more than a year ago. In November 2002, an Ad Hoc Committee composed of members with expertise in pharmaceutical dosage forms, biopharmaceutics, and nomenclature was formed to work with the PDF EC in this endeavor.
The Stimuli article presented here represents the combined effort of this Ad Hoc Committee and the PDF EC. Portions of the PDF EC–approved taxonomy charts and glossary were subsequently revised by members of the Ad Hoc Committee for clarity and to address nomenclature issues. This article is the first step in the public review and comment process. Further modifications to the taxonomy scheme and glossary are anticipated.
Readers are invited and encouraged to submit comments and suggestions regarding the completeness, clarity, and utility of this taxonomy scheme and glossary. Receipt of such comments will facilitate revision of the taxonomy chart and glossary and their advancement in the revision review/adoption process.

INTRODUCTION
As part of its assignment to revise General Chapter <1151> Pharmaceutical Dosage Forms, the Pharmaceutical Dosage Forms Expert Committee (PDF EC) undertook during 2002 the development of a taxonomic scheme for the categorization of pharmaceutical dosage forms. The intent is that this scheme will clarify the content of USP–NF and make it more user-friendly. The taxonomy and its associated glossary provide the following benefits to users of the compendia:
  • a uniform way of categorizing pharmaceutical dosage forms;
  • a tool for finding information and linking specific dosage form monographs and general chapters;
  • a rational linkage between dosage forms and their compendial specifications; and
  • a linkage between dosage form drug substance(s) and therapeutic use.
In particular, if individual dosage forms can be more easily linked with their specifications or performance tests, both the manufacturer and the regulator will have a much clearer knowledge of the specifications generally needed to demonstrate compliance. Development of this taxonomy is also seen by USP as a mechanism for linking the endeavors of other USP Expert Committees, the Food and Drug Administration (FDA), Health Level 7 (HL7) (1), and the International Conference on Harmonization (ICH) in this field. It has been reported that FDA has a goal to standardize the established names of dosage forms to facilitate electronic transactions within the Agency.
In an effort to standardize names, FDA is also looking at nomenclature use in other countries. FDA and the USP Expert Committee on Nomenclature and Labeling work together on USP nomenclature for new products for which there are no USP dosage form descriptors. Many of the FDA and USP terms match or are close—but many of them do not match. The CDER Data Standards Manual has many dosage forms that USP does not have.

TAXONOMY
The currently suggested taxonomy chart was developed by the PDF EC with assistance from members of the Biopharmaceutics Expert Committee and the Nomenclature and Labeling Expert Committee. This chart is based on the tier concept, with the first tier delineating dosage forms according to the route of administration by which the drug substance is delivered.
The second tier is based on the general type of dosage form involved and its physical properties, i.e., solid, semi-solid, liquid, gas, or aerosol. Each one of these groupings contains its own subsections listing the specific presentation of the dosage form, e.g., tablet, cream, insert, etc. This second tier facilitates downward expansion into the third tier, which is based on the type of release pattern of the drug substance and performance characteristics of the dosage form.
With such a scheme, any dosage form for any drug substance can be unambiguously identified by a combination of taxonomic terms from each tier, taking the form:
[drug substance] [route of administration] [physical state] [release pattern].

GLOSSARY
The glossary contains an introductory statement indicating that the definitions are for information only and for use in understanding the pharmaceutical dosage forms taxonomy. In the interest of the ongoing harmonization efforts, the terms used in the taxonomy and glossary generally correspond with those definitions used by FDA, EP, and JP. Dosage form listings in the glossary follow the convention used in USP monograph titles.
The glossary has two parts. Except where indicated, the first part includes definitions associated with those dosage forms that appear in USP monograph titles, i.e., that appear in the taxonomy scheme, plus certain terms that have been agreed upon by USP and FDA but are not yet used in USP monograph titles.
The second part of the glossary includes definitions of some nonpreferred and/or outdated terms that are included only for completeness and electronic searching but with a notation directing the user to the preferred terms in Part 1. It also includes definitions of other terms that are not acceptable for use in USP–NF but are deemed to be helpful to the reader because they provide information about dosage form terminology used in other regions.
The general information chapter á1151ñ Pharmaceutical Dosage Forms will not contain subheadings for, or disquisitions on, the dosage form terms contained in Part 2 of the glossary.

CONCLUSION
In developing this taxonomy and glossary, every effort was made to keep them as simple as possible and to avoid duplication. This is viewed by USP as a positive move that may make USP–NF more user-friendly. Specifically, it will facilitate electronic searches in a manner that is not currently possible.
It should also be obvious that the taxonomic convention will facilitate the identification of clear associations between related groups of dosage forms and logical standards that should be uniformly applied. Consequently, in accordance with the tests and general chapters (or lack thereof), USP Expert Committees could be assigned or Advisory Panels could be formed to develop and revise the needed tests and general chapters, e.g., an Advisory Panel on Topicals or one on Performance Tests.
In the future it likely will be necessary to expand the number of categories in this taxonomy and glossary to accommodate entirely new types of dosage forms as required by the novel sources of drug substances now beginning to emerge. Likewise, there is Expert Committee agreement that this taxonomy should not limit new naming conventions. It is vital that new dosage form names be published in USP–NF to publicly announce the establishment of new dosage forms because FDA uses USP–NF as an information source for dosage-form nomenclature. There are also global implications associated with this nomenclature process, e.g., harmonization via ICH and HL7.

PUBLIC COMMENTS ABOUT THE TAXONOMY
Reader comments regarding the suggested taxonomy and glossary are invited. These comments should be submitted to Dr. W. Larry Paul at USP Headquarters, 12601 Twinbrook Parkway, Rockville, MD 20852-1790, by 28 November 2003.

REFERENCE
  1. Founded in 1987, Health Level Seven, Inc. (http://www.HL7.org) is a not-for-profit, ANSI-accredited standards developing organization whose mission is to provide a comprehensive framework and related standards for the exchange, integration, sharing, and retrieval of electronic health information that supports clinical practice and the management, delivery, and evaluation of health services. Its 2200 members represent more than 500 corporate members, including 90 percent of the largest information systems vendors serving health care. HL7 has the specific goal to create flexible, cost-effective standards, guidelines, and methodologies to enable health care information system interoperability and sharing of electronic health records. The HL7 data interchange standards have been recommended by the National Committee on Vital and Health Statistics (NCVHS) for national adoption within the United States.
    HL7 has created ANSI standards for the transmission of drug orders, drug dispensing, and patient drug administration transactions. In this context, it is essential that the codes used for drugs be accurate, readily available, easy to use, and stable. Drug codes that meet these qualifications can be used for detecting drug–drug interactions, dosing errors, and drug allergies, as well as efficient reporting of adverse drug events. By means of these capabilities, accurate drug codes ultimately lead to decreased costs and improved patient safety.
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GLOSSARY

PART 1
AEROSOL
A product that is packaged under pressure and contains active ingredients that are released upon activation of an appropriate valve system.
CAPSULE
A solid dosage form in which the active, with or without other ingredients, is filled into either a hard or soft shell. Most capsule shells are composed mainly of gelatin.
CHEWABLE
Term applied to a dosage form that is intended to be chewed in the mouth before swallowing.
COLLODION
Liquid preparation composed of pyroxilin dissolved in a solvent mixture of alcohol and ether and applied externally.
CONCENTRATE
A dosage form that is intended to be diluted with a vehicle before use. This term is being phased out of USP titles.
CREAM
A dosage form comprising a viscous semisolid emulsion.
DELAYED RELEASE
Release pattern of the active from the dosage form is deliberately modified to delay release of the active for some period of time after initial administration.
DENTAL
Term applied to a dosage form that is applied to the teeth and/or gums for localized action.
EFFERVESCENT
Term applied to a dosage form, frequently tablets, containing ingredients that, when in contact with water, rapidly release carbon dioxide. The dosage form is dissolved or dispersed in water before administration.
EMULSION
A two-phase system in which one liquid is dispersed throughout another liquid in the form of small droplets. When an aqueous solution is the continuous phase, the system is designated an oil-in-water emulsion. Conversely, when oil is the continuous phase, the system is designated a water-in-oil emulsion.
EXTENDED RELEASE
Release pattern of the active from the dosage form is deliberately modified to slow down the rate of release compared to that of a conventional (immediate-release) form of the same active. The term is synonymous with PROLONGED RELEASE.
FOAM
An emulsion packaged in pressurized aerosol containers; when dispensed it has a fluffy, semisolid consistency.
GEL
A dispersion of small inorganic particles or a solution of large organic molecules rendered jellylike in consistency.
GUM
A dosage form in which the base consists of a plastically deforming material that, when chewed, releases the active into the oral cavity.
IMMEDIATE RELEASE
Synonymous with CONVENTIONAL RELEASE (see Part 2), i.e., the release pattern of active from a dosage form in which no deliberate effort has been made to modify the rate. In the case of capsules and tablets, the inclusion or exclusion of a disintegrating agent is not interpreted as a modification. IMMEDIATE RELEASE is the preferred term.
INHALATION
A dosage form designed to be dispersed in a current of air and drawn into the airways when the patient breathes in.
INJECTION (INJECTABLE)
A sterile dosage form injected into a body cavity, fluid, or tissue.
INSERT
A solid dosage form which is inserted into a body cavity, such as the urethra or vagina. See also SUPPOSITORY, a term used to describe inserts into the rectal region.
IRRIGATION
A sterile solution intended to bathe or flush open wounds or body cavities.
INTRAOCULAR
A sterile liquid dosage form for administration within the eye.
JELLY
Term synonymous with GEL.
LOZENGE
A solid dosage form intended to disintegrate or dissolve slowly in the mouth and usually prepared by compaction in a manner similar to that of tablets or by a molding process.
MODIFIED RELEASE
Release pattern of the active from the dosage form has been deliberately changed from that of a conventional (immediate-release) form of the same active.
NASAL
Term applied to a dosage form administered to the nasal cavity for local or systemic effect.
OCULAR
See INTRAOCULAR.
OIL
A liquid or liquefiable-on-warming solid that is insoluble in water but soluble in ether.
OINTMENT
A viscous oleaginous or polymeric semisolid dosage form.
OPHTHALMIC
A sterile dosage form administered to the external parts of the eye.
ORAL
Term applied to dosage forms that are to be delivered into the mouth and are often swallowed.
ORALLY DISINTEGRATING
A solid oral dosage form that disintegrates rapidly in the mouth.
OTIC
Term for dosage forms to be administered to, or by way of, the ear. Sometimes referred to as AURAL (see Part 2).
PASTE
A semisolid preparation with a stiff consistency containing a relatively high concentration of solids.
PELLET
A solid dosage form of a granular or regular shape.
PLASTER
A solid or semisolid mass supplied on a backing material and intended to provide prolonged contact with the skin.
POWDER
A solid, or mixture of solids, that has been reduced to a finely divided state.
RECTAL
Term applied to dosage forms that are to be delivered into the rectal region to provide local or systemic effect.
RINSE
A solution used to cleanse by flushing.
SHAMPOO
A solution or suspension used to clean the hair and scalp.
SOAP
The alkali salt(s) of a fatty acid or mixture of fatty acids.
SOLUTION
A liquid preparation that contains one or more chemical substances dissolved, i.e., molecularly dispersed, in a suitable solvent or mixture of mutually miscible solvents.
SUBLINGUAL
A term applied to a dosage form that is intended to be placed underneath the tongue and to release the active for absorption in that region.
SUPPOSITORY
A solid dosage form in which one or more actives is dispersed in a suitable base and molded or otherwise formed into a suitable shape for insertion into the rectal area to provide local or systemic effect.
SUSPENSION
A liquid preparation that consists of solid particles dispersed throughout a liquid phase in which the particles are not soluble.
TABLET
A solid dosage form prepared from a powder or mixture of powders by compaction, by molding, or by means of lyophilization.
TINCTURE
An alcoholic or hydroalcoholic solution prepared from vegetable materials or from chemical substances.
TOPICAL
Term applied to dosage forms that are intended to be applied to the outer surface of the body.
VAGINAL
Term applied to solid dosage forms administered to the vagina, typically to obtain local effect.

PART 2
AROMATIC WATER
A clear, saturated aqueous solution of volatile oils or other aromatic or volatile substances.
AURAL (Auricular)
An unofficial alternative to OTIC (see Part 1) for administration to, or by way of, the ear.
BEAD
A solid dosage form in the shape of a small sphere. In most products a unit dose would consist of multiple beads. (See also PELLETS.)
COATED
Term applied to a solid dosage form that is covered by deposition of an outer solid that is different in composition from the core material.
CONVENTIONAL RELEASE
Release pattern of active from a dosage form in which no deliberate effort has been made to modify the rate. In the case of capsules and tablets, the inclusion, or exclusion, of a disintegrating agent is not interpreted as a modification. IMMEDIATE RELEASE (see Part 1) is synonymous with this term.
ELIXIR
A clear, pleasantly flavored, sweetened hydroalcoholic liquid containing dissolved actives intended for oral use. The term is no longer used in USP–NF (see Part 1 [ORAL][SOLUTION] or [ORAL][SUSPENSION]).
EMOLLIENT
A bland, fatty, or oleaginous substance applied locally to the skin to increase the tissue moisture content.
EXCIPIENT
An ingredient of a dosage form other than an active.
GRANULES
Preparations composed of dry aggregates of powder particles that may contain one or more actives, with or without other ingredients. They may be swallowed as such, or dispersed or dissolved in water. Granules are frequently compacted into tablets, with or without additional ingredients.
HARD-SHELL CAPSULE
A solid dosage form in which one or more actives, with or without other ingredients, is filled into a two-piece shell. Most hard-shell capsules are composed mainly of gelatin and are fabricated prior to the filling operation (see CAPSULES in Part 1).
LOTION
A fluid suspension or emulsion applied to the outer surface of the body. The term is no longer used in USP–NF (see Part 1 [TOPICAL][EMULSION] or [TOPICAL][SUSPENSION] or [TOPICAL][SOLUTION]).
MOLDED TABLET
A tablet that has been formed by dampening the ingredients and pressing them into a mold, then removing and drying the resulting solid mass.
MOUTHWASH
Term applied to an aqueous solution used to rinse the oral cavity.
ORO-PHARYNGEAL
Term applied to dosage forms in which the active is released into the buccal cavity and/or pharyngeal region to exert a local or systemic effect.
PILL
A solid spherical pharmaceutical dosage form, usually prepared by a wet massing technique. The use of the term PILL to describe tablets or capsules is discouraged.
SPIRIT
A liquid dosage form comprised of an alcoholic or hydroalcoholic solution of volatile substances.
STRIP
A dosage form or device in the shape of a long, narrow, thin solid material.
SYRUP
A solution containing high concentrations of sucrose or other sugars. The term is no longer used in USP–NF (see Part 1 [ORAL][SOLUTION] or [ORAL][SUSPENSION]).
TAPE
A dosage form or device in the shape of a long, narrow, solid material, frequently constructed of plastic or fabric.
TROCHE
A solid dosage form intended to disintegrate or dissolve slowly in the mouth and usually prepared by compaction in a manner similar to that of tablets. Also frequently referred to as LOZENGE (see Part 1).
URETHRAL
A term applied to a dosage form intended for insertion into the urethra to provide a local effect of the contained active.