United States Adopted Names naming guidelines

What is a USAN and how is it different from a brand name?

By definition, nonproprietary names are entirely in the public domain and are not subject to trademark rights. A United States Adopted Name (USAN) is a nonproprietary name selected by the USAN Council to ensure safety, consistency and logic in the choice of names. These principles take into account the existence of trademarks, international harmonization of drug nomenclature, new classes of drugs and the fact that the intended uses of substances for which names are being selected may change. 

USAN are assigned to the active drug ingredient, while brand names are usually associated with a specific product. Brand names are company or product specific, can change from country to country, and may even be used for two different active ingredients. The generic name of an active ingredient (e.g., USAN or International Nonproprietary Name [INN]) does not change across national boundaries, companies, or product lines. 

Brand: Cialis™
Generic: tadalafil

Brand: Colemin™, Lipex™, Zocor™ and Vytorin™
Generic: simvastatin

Brand: Gleevec™, Glivec™
Generic: imatinib mesylate

The USAN Council has been assigning names since the early 1960s. The Code of Federal Regulations states that the USAN is an established name for a drug.

What does the USAN program name?

The USAN Program names over 200 substances each year. We provide USAN designations for: 

• Small-molecule drugs or chemical substances
• Biotechnology drugs including monoclonal antibodies, therapeutic vaccines, proteins and peptides, DNA, RNA, nucleoside, and nucleotide therapies
• Gene therapies
• Cellular therapies and related substances
• Other biological substances deemed appropriate to be assigned a USAN by the USAN Council
• Contact lens materials
• Active ingredients in sunscreens
• Veterinary products intended to control diseases in animals
• The base, salt, ester, or other chemical derivative of a substance that has received a USAN

Generally, the USAN Council declines to name the following substances:

• Mixtures that do not have an IND number or that do not require approval for human use by the FDA
• Bacterial strains
• Drug delivery mechanisms
• Excipients alone
• Prophylactic vaccines intended to prevent illnesses (such as the COVID vaccine or the flu shot)
• Product formulations (emulsions, suspensions, etc.)
• Medical devices
• Manufacturing processes
• Combination drug products

USAN general principles 

1) A nonproprietary name should be useful primarily to health care practitioners, especially physicians, pharmacists, nurses, educators, dentists, and veterinarians.

• The first way the USAN Council judges usefulness is suitability, which includes safety for use in routine prescribing, ordering, dispensing, and administering drugs in the U.S.
• Second, the name should be suitable for use in educational programs for medically oriented professions and in scientific and lay publications.
• Third, names should be suitable for use internationally in drug identification, the exchange of information, and translation into different languages.

2) Attributes that contribute to usefulness are simplicity (i.e., brevity and ease of pronunciation), euphony, ready recognition, and recall.

• The name for the active moiety of a drug should be a single word, preferably with no more than 5 syllables.
• The name for the active moiety may be modified by a single term, 5 syllables or shorter, to show a chemical modification, such as salt or ester formation (e.g., cortisone acetate, cefamandole sodium, or erythromycin acistrate).
• Only rarely, under compelling circumstances, does the USAN Council accept a name with more than 1 modifying term. For example, pharmaceuticals containing radioactive isotopes may have names longer than two words 

3) Characteristics and relationships reflected in a name should be of practical value to health care providers and patients.

• A common, simple word element (a "stem") should be incorporated in names of all members of a group of related drugs when pertinent, common characteristics can be identified (e.g., similarity of pharmacological action). However, when pharmacological similarity is found in drugs of distinctly different chemical nature, stems should differ.
• Some classes of drugs (e.g., monoclonal antibodies, gene therapies, insulins, erythropoetins) have nomenclature rules that are specific to that class. These rules are followed for all members of that class.
• When a substance to be named has an existing common name or other name by which it is widely recognized, the common name may be preferred to a stem-based name. Examples of such names include resveratrol, curcumin and ribitol.

4) A name should not conflict, mislead or be confused with other nonproprietary names and with established trademarks, and USAN stems should not be incorporated into Trade Names (more information on the Protection of USAN & INN Stems can be found here).

5) Names with established usage (e.g., a common name) may be preferred if they conform to these general principles, the specific nomenclature rules described later, and do not conflict with existing nonproprietary names and trademarks.

6) Where possible, the USAN Council assigns substances to existing stems or nomenclature schemes describing the substance, its action or its use. A new stem will be created only in unusual circumstances where existing stems and nomenclature schemes do not accurately represent a compound, its action, structure or use, and also when substantial preclinical and clinical data support the creation of a new stem.

7) Identical negotiations submitted by 2 or more manufacturers will be conducted in accordance with the Council's confidentiality practices. The applicants involved will not be notified of the multiple sources of the submission. However, the name selected by the USAN Council will need to be accepted by each sponsor involved in the negotiation process. 

8) A USAN request should be made after the drug sponsor has submitted an Investigational New Drug (IND) Application to the Food and Drug Administration to obtain permission to initiate studies on humans. An IND number is required before the USAN application review process can begin.             

9) Negotiations may be placed on hold.

• The USAN Council Secretariat will put an ongoing negotiation on hold for 6 months, plus 1 additional 3-month extension, upon receipt of a written request from the manufacturer. Once the USAN Council has selected a name candidate and recommended a name, applicants have up to 6 months to respond to the USAN Council’s decision before the file is closed.
• If the negotiation is to be reopened at a later time, it will be treated as a new application and will be assigned a new USAN file number. The manufacturer will be expected to submit a new USAN application form, update the background information and submit the appropriate fee.

10) USAN pronunciations are included in the statement of adoption but are finalized after review by experts at USP. For more information about recommended pronunciations, see our pronunciation guide.

Understanding the parts of most USAN names

Several decades ago, when the USAN Program first began coining names (and even before its inception), condensing the systematic chemical name of a substance was a common way to coin drug names. This is no longer the case.

Now, new names consist of 3 parts: 

• Prefix: Means nothing; differentiates drug from others in class
• Infix: Used occasionally; further subclassifies a drug
• Stem: Indicates place in nomenclature scheme; drugs with the same stem are related. The USAN Stem List is here.

Stems are usually at the end of a name, with a few exceptions (e.g., cef-), and indicate the drug's place within the nomenclature scheme. Consequently, a new suffix often but not always suggests a new mechanism of action. Drugs with the same ending (stem) belong to the same pharmacologic family. Infixes, appearing in the middle of the word, are sometimes used to further classify the drug. Prefixes mean nothing. The sole purpose of a prefix is to differentiate a drug from other members of the class.

As an example, consider sildenafil (Viagra™), vardenafil (Levitra™), and tadalafil (Cialis™). The -afil stem is formally defined as for PDE5 (phosphodiesterase 5) inhibitors. The -den- infix indicates that sildenafil and vardenafil have similar chemical structures. The prefixes are sil-, var- and tadal-.

How USAN stems are used

A list of all the stems/pharmacologic families USAN has designated is here. 

Group relationships in a name preferably should be indicated by use of syllables or stems. Conversely, use of the stem for other than the appropriate group should be avoided. When multiple stems are available, the stem conveying the most information should be used.

The following are a few examples of brand names, with the generic name and an explanation of what it means. 

Lipitor™ (atorvastatin calcium) and Crestor™ (rosuvastatin)
Stem and meaning: enzyme inhibitors (-stat); inhibitors of HMG-CoA, an enzyme involved in synthesizing cholesterol (-vastatin)

Prilosec™ (omeprazole magnesium) and Prevacid™ (lansoprazole)
Stem: -prazole
stem and meaning: -prazole, agents to treat ulcer and/or heartburn that are chemically related to benzimidazole

Singulair™ (montelukast)
stem and meaning: -lukast, antiallergics and antiasthmatics that are leukotriene receptor antagonists

Plavix™ (clopidogrel sulfate)
stem and meaning: -grel, platelet aggregation inhibitors

Effexor XR™ (venlafaxine hydrochloride)
stem and meaning: -faxine, antianxiety, antidepressant inhibitor of norepinephrine and dopamine reuptake

Cymbalta™ (duloxetine hydrochloride)
stem and meaning: -oxetine, antidepressants with a chemical structure related to fluoxetine

Diovan™ (valsartan)
stem and meaning: -sartan, angiotensin II receptor antagonists

Valtrex™ (valacyclovir)
Stem: -vir
meaning: antiviral compounds
stem subgroup: -cyclovir
meaning: chemical structure is related to acyclovir

There are some prefixes and infixes with specific, defined meanings, some of which have been used to coin names for top-selling drugs. 

• Ar-, es-, lev- and dex- are used to name stereoisomers of drugs that have already received a USAN (see the rules for stereoisomers below for their use)
• Peg- means that a biologic substance, such as peptide, is pegylated. 
• An -io- infix denotes a high iodine content (amiodarone).
• -fos-, appearing anywhere in a drug name, means phosphorous is present, often as a phosphate ester.
• Ef- or -ef- in the name of a protein or peptide means that there is a fragment crystallizable (Fc) region

Specific nomenclature rules for prefixes

USAN/INN have specific rules that govern the selection of prefixes and apply more generally to syllables and letters that appear anywhere within the names. The USAN Council cannot accept names that do not follow these specific rules about letters and combinations of letters.  

1) Prefixes incorporating an obvious reference to the indication of a drug, or its pharmacology, the company that developed it, or a quality of the drug (e.g., dura- to indicate long duration of action) are not accepted by the USAN Council. Prefixes that imply "better," "newer" or "more effective;" prefixes that evoke the name of the sponsor, dosage form, duration of action or rate of drug release should not be used (e.g., "dura," "forte," or "efex"). 

2) Prefixes that refer to an English, Latin or Greek number, unless meaningful to the compound, are not acceptable (e.g., "deci," "centi," "bi" or "di").

3) Prefixes with an anatomical connotation or referring to a medical condition are not acceptable.

4) Prefixes that indicate a chemical element or compound (Ca, Ni and Stannous) are not acceptable.

5) Because of the international exchange of drug information, specific guidelines have been formulated to ensure appropriate translation of nonproprietary names into other languages. These rules of preferred phonetic spelling should be used:

• The letter "f" should be used instead of "ph"
• The letter "t" should be used instead of "th"
• The letter "e" should be used instead of "ae" or "oe"
• The letter "i" should be used instead of "y"
• Avoid the letter "h"
• Avoid the letter "k"
• Avoid the letter "j"
• Avoid the letter "w"
• "ar," "rac," "lev," "dex," or "es" are reserved for stereochemical configurations

6) Additionally, these letter combinations are restricted until further notice:

• Avoid the beginning letter combination of "me"
• Avoid the beginning letter combination of "str"
• Avoid chemical connotations such as "ben," "bu," "cat," "cel," "fen," "flu," "fo(s)" and "piro," unless chemically appropriate
• Avoid chemical symbols unless present in the compound "al," "ba," "ca," "li" and "ni"
• Avoid "z" or "x" as a beginning letter
• Avoid blends of 2 consecutive vowels
• The letter q should be followed by a u and another vowel to facilitate pronunciation.
• The use of doubled consonants should be avoided.

7) Individual letters, numbers or hyphenations are restricted to those groups of substances for which usage fulfills a clearly demonstrable purpose (e.g., interferon alfa-2b, paflufocon A or technetium Tc 99m siboroxime).

Rules for specific types of substances

There are rules and nomenclature schemes that are applicable to specific types of substances, such as salts or esters, monoclonal antibodies, and contact lens polymers. These substances are listed below alphabetically by class, with links to the appropriate nomenclature schemes or more details for that substance.

Bioengineered or Synthetic Proteins

Cell therapies

Colony Stimulating Factors

Complexes

A name for a complex of 2 or more components should list the name of the principal active ingredient followed by a coined designation for the second component ending with an "-ex" suffix to indicate "complex" (e.g., bisacodyl tannex, doxycycline fosfatex). Complexes formed from sulfonated diethenylbenzene-ethenylbenzene copolymers and an active ingredient should list the name of the principal active ingredient followed by "polistirex," such as in chlorpheniramine polistirex or codeine polistirex.

Conjugates

Conjugates, in which a payload is attached, directly or via a linker, to a carrier that provides targeted delivery, normally require names that are two or more words in length. There are specific rules for naming conjugates:

• Antibody-drug conjugate names consist of a name for the monoclonal antibody, followed by the name for the combination of linker and payload. See the rules for naming monoclonal antibodies for more detailed information, and the USAN stem list for common suffixes for payloads.
• Peptide conjugates are named with a word for the peptidic portion ending in -tide followed by a second word for the payload and linker combination. Often, the payload for peptide conjugates is a chelater bound to a radiolabel. If so, the radiolabel is listed first, following USAN conventions for naming radiolabeled substances. It is followed by the designations for the peptide and the linker.
• In conjugates of oligonucleotides and peptides, the name for the oligonucleotide is listed first (e.g., -rsen), followed by the name for the peptide (e.g., -tide). 

Contact Lens Polymers

Erythropoietins

The word epoetin is used for recombinant human erythropoietin, followed by the appropriate Greek letter (spelled out). "Epoetin" describes erythropoietin preparations that have an amino acid sequence identical to the endogenous cytokine; the words alfa, beta, gamma, etc., are added to designate preparations that differ in the composition and the nature of the carbohydrate moieties.

Esters and Pharmaceutical Salts

1) The name for the active moiety may be modified by a single term, preferably of no more than 4 syllables, to show a chemical modification, such as salt or ester formation (e.g., cortisone acetate, cefamandole sodium or erythromycin acistrate).

2) Brevity and ease of use are given more weight in choosing names for salts and esters than adhering to principles of chemical nomenclature. Consequently, hyphens and numbers to indicate position, and words like “acid” to indicate protonation of a carboxylic acid, are not used in USAN designations.

3) Only under compelling circumstances is a name with more than 1 modifying term acceptable. Rarely, a second modifying term may be added for a substance that has more than one ester moiety or both an ester and salt modification. However, the historical preference has been to coin a new modifier that includes both the salt and the ester.

4) Esters, salts, chelates, prodrugs, and complexes ordinarily require a 2-word name to indicate the inactive as well as the active portion.

• The preferred order for the name of a simple inorganic salt is cation-anion (e.g., sodium chloride), irrespective of the clinically significant portion. The same order is preferred for well-known salts of simple organic acids (e.g., sodium lactate, magnesium citrate, potassium acetate).
• For most pharmaceutical substances, the pharmacologically active portion should be identified first (e.g., oxacillin sodium, dexibuprofen lysine).
• A name for a salt or ester is generally derived from the name of the pharmacologically active moiety or corresponding acid (e.g., chloroprednisone acetate).
• Ester prodrugs, which are cleaved in vivo to release the pharmacologically active species, ordinarily receive 2-word names (e.g., haloperidol decanoate, clindamycin palmitate). Other types of prodrugs may receive a 1- or 2-word name, as the USAN Council deems.
• Exceptions to 2-word names may be most appropriate when differences in pharmacologic activity for the ester form are clinically important (e.g., if only the ester but not the parent is pharmacologically active). To receive a 1-word designation for an ester, sponsors must submit data to document the activity of the ester. The USAN Council may request such information if it is not provided.
• As of January 2013, the name for the salt form of a pharmacologically active moiety no longer specifies stoichiometry. Between January 1993 and December 2012, numerical prefixes were often used to specify this (e.g., basalazide disodium).

5) A name for a quaternary ammonium substance should designate the cation and anion separately (e.g., octonium bromide not octonine methylbromide). The name assigned to the cation must contain the -ium suffix stem. This rule is modified when a 2nd, more pertinent, stem is used. In such cases, the addition of the -ium suffix stem to solely designate a quaternary ammonium is not required.

6) Official names have been selected for many radicals and adducts used to form salts or esters of the pharmacologically active moiety.  Most of these names are contractions of the chemical name assigned to the radical or adduct. Sometimes, the official name identifies a multicomponent adduct, such as a salt combined with an ester. The list of modifiers for radicals, anions and salts can be found here (PDF).

Gene Therapies

Naming rules

Glycosylated proteins

For most glycosylated proteins, a Greek letter (e.g., alpha, beta) is appended to the name to indicate glycosylation patterns, except for monoclonal antibodies. For monoclonal antibodies, no Greek letter is used. Additionally, USAN does not issue a new name to a monoclonal antibody that is glycosylated differently but has the same sequence as an antibody that already has a USAN designation.

Hydrates

A name for a substance does not indicate the state of hydration, the morphology, or the mode of preparation. Reference to the water of hydration is retained in the chemical information (chemical names, formulas, weight) but is excluded from the nonproprietary name. The degree of hydration becomes a part of the chemical entity identified by the USAN. When there are multiple states of hydration, additional CAS registry numbers may be listed for other states of hydration to indicate this.

Inorganic salts

The preferred order for the name of an inorganic salt is cation-anion (e.g., sodium chloride), irrespective of the clinically significant portion. The same order is preferred for well-known salts of simple organic acids (e.g., sodium lactate, magnesium citrate, potassium acetate).

Interferons

Interleukins

Monoclonal Antibodies

Orphan Drugs

Under the terms of the Orphan Drug Act of 1983, the development and marketing of drug products that are of limited commercial application but are potentially useful in relatively rare disease conditions are encouraged. The selection of a name for an orphan drug may be based on special considerations. Therefore, when the name for an orphan drug appears to follow a more chemically oriented terminology style than is customary for drug nomenclature, this is not a precedent for a future USAN.

Radiolabeled Substances

A name for a drug containing a radioactive atom should list, in the order given: (1) the name of the drug containing the radioactive atom, (2) the element symbol, (3) the isotope number and (4) the name of the carrier agent if any (e.g., rose bengal sodium I 131, cyanocobalamin Co 60, potassium bromide Br 82, technetium Tc 99m butilfenin, technetium Tc 99m medronate, indium In 111 oxyquinoline, indium In 111 satumomab pendetide).

Stereoisomers

A name coined for a new chemical entity routinely does not specify the stereoisomeric form of the molecule in the nonproprietary name. If the stereochemical configuration has been determined, this information is presented in the chemical name(s) and is reflected in the structural formula. A USAN can, therefore, identify the racemic mixture (e.g., carnitrine, ibuprofen, tetramisole) the levo isomer (e.g., remoxipride, quadazocine) or the dextro form (e.g., butopamine). Subsequently, if a name is needed for a different enantiomer or for the racemic form, the following prefixes should be added to the existing name:

• For the racemate, the rac-/race- prefix is used (e.g., racemethionine, racepinephrine, ractopamine).
• For the levorotatory form, the "(S)" isomer, the lev-/levo- prefix is used (e.g., levocarnitine, levamisole, levcromakalim and levdobutamine).
• For the levorotatory form, the "(R)" isomer, ["R(-)"-isomer], the "ar-" prefix is added to the base name.
• For the dextrorotatory form, the "(R)" isomer, the dex-/dextro- prefix is used (e.g., dexamisole, dexibuprofen, dextroamphetamine, dexverapamil, dexrazoxane, dexfosfoserine and dexniguldipine)
• For the dextrorotatory form, the "(S)" isomer ["S(+)"-isomer], the "es-" prefix is added to the base name.