Drug Nomenclature: IUPAC, USAN, WHO, and INN

Drug Nomenclature: IUPAC, USAN, WHO, and INN

Understanding drug names is crucial for pharmaceutical science, clinical practice, and regulatory affairs. Key organizations include:

  • International Union of Pure and Applied Chemistry (IUPAC)
  • United States Adopted Names (USAN) Council
  • World Health Organization (WHO)
  • International Nonproprietary Names (INN) program

Learning Objectives

  • Name drugs as per IUPAC, USAN, and INN standards.

Introduction to Drug Nomenclature

  • Standardized Naming Importance

    • Critical for patient safety, accurate prescription writing, scientific communication, and regulatory documentation.
    • Inconsistent nomenclature can lead to dangerous medication errors.

  • Multiple Naming Systems

    • Drugs have chemical names (structure), nonproprietary (generic) names (clinical use), and brand names (marketing).
    • Each name serves a unique purpose in the drug's lifecycle.

  • Key Organizations

    • IUPAC (chemical structure).
    • USAN Council (United States generic names).
    • WHO's INN Program (international generic names).
    • National regulatory bodies (approve and monitor drug names).

IUPAC Nomenclature

  • Chemical Identity: Provides precise structural identification.
  • Systematic Rules: Based on functional groups and molecular structure.
  • Universal Language: Enables global scientific communication.
  • IUPAC establishes a system for naming chemical compounds based on molecular structure, creating unambiguous identifiers.
  • IUPAC names provide a universal language for chemists and pharmaceutical scientists and contain complete structural information, invaluable in research settings.

IUPAC Naming Rules

  1. Select Parent Structure: Identify the main chain or ring system.
  2. Identify Functional Groups: Determine principal functional groups according to hierarchical preference rules (carboxylic acids typically have the highest priority).
  3. Number the Structure: Assign position numbers to atoms and substituents, ensuring the principal functional group receives the lowest possible number.
  4. Name Substituents: Identify and name all side chains and additional functional groups as prefixes or suffixes.

IUPAC nomenclature follows a logical, systematic approach, ensuring any chemist can deduce the exact structure from the name alone.

IUPAC Example: Acetaminophen

  • Systematic Name Components: N-(4-hydroxyphenyl)acetamide.

    • N- indicates substitution on a nitrogen atom.
    • 4-hydroxyphenyl identifies a benzene ring with a hydroxyl group at position 4.
    • Acetamide refers to the amide formed from acetic acid.

  • Structural Logic: The name describes how an acetamide group connects to a 4-hydroxyphenyl group through a nitrogen atom.

  • Practicality vs. Precision: Simpler names like "acetaminophen" (US) or "paracetamol" (international) are used for everyday use, while the IUPAC name provides unambiguous structural information for scientific research and regulatory documentation.

Limitations of IUPAC Names

  1. Complexity
  2. Pronunciation
  3. Memorization
  4. Clinical Relevance
  • Names can be extremely long for larger molecules.
  • Difficult to verbalize in clinical settings.
  • Nearly impossible to recall from memory.
  • Limited utility in everyday healthcare.
  • Example: Atorvastatin IUPAC name: (3R,5R)-7-[2-(4-fluorophenyl)-3-phenyl-4-(phenylcarbamoyl)-5-propan-2-ylpyrrol-1-yl]-3,5-dihydroxyheptanoic acid.
  • Limitations necessitated simpler naming systems balancing scientific accuracy with practical usability in healthcare settings, leading to nonproprietary naming systems.

United States Adopted Names (USAN)

  • Organizational Structure: Collaborative effort between the American Medical Association (AMA), the United States Pharmacopeia (USP), and the American Pharmacists Association (APhA).
  • Core Mission: Establishing unique, nonproprietary names for drugs used in the United States, distinct from complex chemical names and trademarked brand names.
  • Naming Philosophy: Prioritizes names promoting medication safety, following logical naming patterns, and reflecting relationships between pharmacologically similar compounds. Names must be distinctive, pronounceable, and memorable for clinical use.

USAN Naming Process

  1. Application Submission: Pharmaceutical company submits an application to the USAN Council during Phase II or III clinical trials, including proposed names and detailed information about the compound’s structure and pharmacology.
  2. Scientific Review: The Council’s scientific experts evaluate the drug’s chemical structure, pharmacological class, and mechanism of action, considering how the proposed name reflects these characteristics and follows naming conventions for similar compounds.
  3. INN Coordination: The USAN Council works closely with the WHO’s INN Program to ensure global consistency, preventing situations where a drug might have different generic names in different countries.
  4. Name Adoption: After review and modifications, the Council officially adopts the USAN, publishing it in the USAN Dictionary and other official resources, becoming the standard nonproprietary identifier for the drug in the United States.

USAN Naming Guidelines

  • Pronounceability: Names should be pronounceable in English and ideally not exceed four syllables.
  • Relational Elements: Names should reflect pharmacological relationships through common stems or affixes (e.g., statin drugs for cholesterol lowering share the "-statin" suffix).
  • Distinctiveness: Names must be sufficiently distinct from existing drug names to prevent confusion in written or verbal communications.

USAN Name Components

  • Follows a structured format consisting of a prefix, an optional infix, and a stem.

    • The prefix serves as a unique identifier.
    • The infix, when present, provides additional sub-classification information.
    • The stem indicates the drug’s pharmacological class or mechanism of action.

USAN Example: Imatinib

  1. Chemical Foundation: 4-[(4-methyl-1-piperazinyl)methyl]-N-[4-methyl-3-[[4-(3-pyridinyl)-2-pyrimidinyl]amino]phenyl]benzamide (complex IUPAC name).
  2. Stem Identification: Classified as a tyrosine kinase inhibitor, placing it in the "-tinib" class.
  3. Prefix Selection: The unique prefix "ima-" distinguishes this tyrosine kinase inhibitor from others in its class, forming "imatinib."
  4. Salt Form Addition: Formulated as a mesylate salt, resulting in the name "imatinib mesylate."

World Health Organization (WHO) and INN

  • Global Health Authority: WHO serves as the directing and coordinating authority on international health within the United Nations system.
  • INN Program Establishment: Established in 1953, the International Nonproprietary Names program emerged from a World Health Assembly resolution to eliminate confusion caused by multiple nonproprietary names for the same substance.
  • Global Harmonization: The INN system provides a universal language for identifying pharmaceutical substances, crucial for global pharmacovigilance efforts, international research collaboration, and cross-border patient care.

INN Selection Process

  1. Application Submission: A pharmaceutical company, research institution, or regulatory body submits a detailed application to the WHO, including the chemical structure, pharmacological data, and proposed names.
  2. Expert Group Review: A specialized INN Expert Group evaluates the application, assessing the name’s scientific appropriateness, linguistic suitability across languages, and potential for confusion.
  3. Publication as Proposed INN: Accepted names are published as "Proposed INNs" in WHO Drug Information, initiating a four-month period for formal objections.
  4. Recommended INN Status: If no objections are received or resolved, the name receives "Recommended INN" status and becomes the official global nonproprietary identifier.

INN Naming Principles

  • Consistency and Harmonization: The INN system aims to provide one unique name for each pharmaceutical substance worldwide.
  • Linguistic Acceptability: Names must function effectively across major world languages, avoiding difficult sounds or negative connotations.
  • Stem-Based Relationships: INNs use common stems to indicate pharmacological relationships between drugs.

INN Stems

  1. Pharmacological Classification
  2. Chemical Relationships
  3. Logical Organization
  • The INN program maintains a collection of over 600 stems and substems.
  • Stems typically appear as suffixes (e.g., -prazole for proton pump inhibitors), but can also function as prefixes (e.g., cef- for cephalosporin antibiotics) or infixes (e.g., -vir- for antiviral agents).
  • Examples include -mab for monoclonal antibodies, -pril for ACE inhibitors, -sartan for angiotensin II receptor antagonists, and -stat for enzyme inhibitors.

INN Example: Adalimumab

  • Prefix: Ada- (unique identifier)
  • Substem 1: -li- (immune system target)
  • Substem 2: -mu- (fully human source)
  • Primary Stem: -mab (monoclonal antibody)
  • Target: Tumor Necrosis Factor (TNF)
  • Therapeutic Use: Treatment of autoimmune diseases
  • Adalimumab deconstructs into meaningful segments that convey information about the drug's nature and function.

Coordination Between USAN and INN

  1. Shared Application Review: When manufacturers apply for both USAN and INN, the respective committees coordinate their reviews to achieve name alignment.
  2. Harmonization Efforts: USAN and INN programs actively work to reconcile naming differences, including systematic reviews of existing names and development of harmonization strategies.
  3. Exception Management: In rare cases where historical differences persist (e.g., acetaminophen in the US vs. paracetamol internationally), both organizations acknowledge these exceptions while preventing new discrepancies.
  4. Joint Stem Development: The organizations collaborate on developing and updating stems for new drug classes.

Comparison of Naming Standards

  • International Nonproprietary Name (INN): paracetamol (en), paracetamolum (la), paracetamol (fr), paracetamol (es), парацетамол (ru)
  • Australian Approved Name (AAN), British Approved Name (BAN): paracetamol
  • United States Adopted Name (USAN), United States Pharmacopeia (USP): acetaminophen
  • Japanese Accepted Name (JAN), Japanese Pharmacopoeia (JP): アセトアミノフェン(jp)

Examples of drugs for which the USAN differs from the INN include:

INNUSAN
glibenclamideglyburide
isoprenalineisoproterenol
moracizinemoricizine
orciprenalinemetaproterenol
paracetamolacetaminophen
pethidinemeperidine
rifampicinrifampin
salbutamolalbuterol
torasemidetorsemide
retigabineezogabine

Examples of Drug Naming

Amphetamine Naming

  1. Chemical Name: dl-2 amino-1 phenylpropane
  2. Generic Name: dl-amphetamine
  3. Trade Name: Benzedrine
  4. Street Names: Speed, bennies, whites

Valium Naming

  1. Chemical Name: 7-chloro-1-methyl-5-phenyl-3H-1,4-benzodiazepin-2[1H]-one
  2. Generic Name: Diazepam
  3. Trade Name: Valium
  4. Street Names: Tranks, downers, blues, yellows

Naming of Biological Products

  • Monoclonal Antibodies: Antibodies follow a naming scheme with the stem "-mab" preceded by source substems: "-u-" (human), "-o-" (mouse), "-xi-" (chimeric), or "-zu-" (humanized). Target substems indicate the disease area, such as "-li-" (immunomodulating) or "-tu-" (tumor).
  • Gene Therapies: Gene therapy products incorporate the infix "-gene-" to identify their mechanism.
  • Cell Therapies: Cell-based products use the suffix "-cel" combined with prefixes indicating the cell type and source.

Challenges in Modern Drug Naming

  1. Structural Complexity: Modern pharmaceuticals often feature complex molecular architectures that defy traditional naming approaches.
  2. Novel Modalities: Emerging therapeutic platforms, such as oligonucleotides, cell therapies, gene therapies, and RNA-based medicines, present unique naming challenges.
  3. Information Density vs. Usability: Drug names must strike a balance between conveying sufficient scientific information and remaining practical for clinical settings.

Impact on Drug Safety

  1. Global Pharmacovigilance
  2. Professional Communication
  3. Medication Error Prevention
  4. Patient Education
  • Standardized drug nomenclature serves as a critical foundation for medication safety worldwide.
  • Consistent nomenclature enables more effective global pharmacovigilance, allowing regulatory authorities to detect safety signals across international boundaries.

Trademark Considerations

  • Separation from Generic Names
  • Regulatory Scrutiny
  • Commercial vs. Safety Interests
  • WHO discourages trademarks derived from INNs or their stems.

Future Trends in Drug Nomenclature

  1. AI-Assisted Naming
  2. Personalized Medicine Adaptations
  3. Unified Global System

Resources for Drug Nomenclature

  • The WHO INN database: Comprehensive access to all International Nonproprietary Names.
  • The USP Dictionary of USAN and International Drug Names: Authoritative compilation of United States Adopted Names.
  • IUPAC's "Nomenclature of Organic Chemistry" (the Blue Book): Definitive guidelines for systematic naming.

Foundation for Communication

  • Standardized drug nomenclature provides a language that enables clear communication about pharmaceuticals.
  • Nomenclature approaches continue to adapt to pharmaceutical innovation.
  • Drug naming systems contribute significantly to medication safety, pharmacovigilance, and equitable access to medicines worldwide.