In October 2021, the WHO’s INN Expert Group voted to retire the single most recognizable suffix in pharmaceutical nomenclature. Every monoclonal antibody approved since 1990 had ended in “-mab.” As of the 73rd INN Consultation, new antibody INNs no longer receive that suffix at all. They receive one of four replacements: “-tug,” “-bart,” “-mig,” or “-ment,” depending on whether the molecule is an unmodified immunoglobulin, an engineered one, a multispecific construct, or a fragment [1]. By 2022, 879 approved and investigational antibodies already carried the old “-mab” suffix, which is why the WHO judged the naming space too crowded to sustain [2].
This is not a cosmetic change. It rewrites how competitive intelligence analysts, patent searchers, and pharmacovigilance teams read a drug name at a glance, and most industry commentary on generic pharmaceutical naming has not caught up with it. This guide covers that reform in full, alongside the rest of the INN and USAN architecture: how stems are built, how names function as a legal disclosure event in patent prosecution, how the FDA’s biosimilar suffix policy has changed twice since 2017, and how naming data doubles as an early-warning system for competitive pipeline tracking.
Quick Answer: How to Read a Generic Drug Name
A generic drug name is built from an invented prefix plus a standardized WHO or USAN stem, usually placed at the end of the word. The stem carries the pharmacological or structural classification; the prefix only distinguishes the compound from others in its class. Reading right to left — stem first, then any infix, then prefix — is the fastest way to classify an unfamiliar compound.
Name part
Position
What it tells you
Example
Stem
Usually suffix
Pharmacological class or antibody format
“-tinib” = kinase inhibitor
Substem/infix
Middle
Target or subclass
“-ci-” = cardiovascular target
Prefix
Beginning
Invented, distinguishes compound within class
“ada-” in adalimumab
Modified INN suffix
Separate word
Salt, ester, or biosimilar distinguishing suffix
“maleate” in enalapril maleate; “-adaz” in adalimumab-adaz
The 2021–2022 Monoclonal Antibody Reform: What Actually Changed
Why the WHO Scrapped “-Mab” Instead of Just Trimming It
Earlier accounts of the 2021 reform, including much of the trade coverage at the time, described it as the WHO dropping only the source substem — the “-u-,” “-zu-,” and “-xi-” fragments that indicated human, humanized, or chimeric origin — while keeping “-mab” itself. That is not what happened. The WHO Expert Group’s actual decision, adopted at the 73rd INN Consultation in October 2021 and published as working document INN 22-542 in 2022, discontinued “-mab” entirely for new assignments and replaced it with four structurally defined stems [1][3].
New stem
Definition
Replaces
-tug
Monospecific, full-length immunoglobulin with unmodified constant regions
Standard “-umab”/”-zumab”/”-ximab” antibodies
-bart
Monospecific, full-length immunoglobulin with engineered (mutated) constant regions
Fc-engineered antibodies previously named like any other “-mab”
-mig
Bispecific or multispecific immunoglobulin, any length or format
Bispecifics such as blinatumomab-type constructs
-ment
Immunoglobulin fragment lacking a full Fc region (Fab, F(ab’)2, scFv-Fc)
Fragment-based biologics previously folded into “-mab”
Source: WHO INN Working Document 22-542, “New INN monoclonal antibody (mAb) nomenclature scheme” [3].
The reform also retired the catch-all “-li-” immunomodulatory substem, splitting it into four more specific target infixes: “-ki-” for cytokine and cytokine-receptor targets, “-ler-” for allergen targets, “-sto-” for immunostimulatory mechanisms, and “-pru-” for immunosuppressive mechanisms [4].
The First Drugs Named Under the New System
Retrospective naming was not part of the reform — every antibody named before the effective date keeps its original “-mab” designation permanently. The new stems apply only to INN applications filed after the scheme took effect. Tegoprubart, the USAN/INN assigned to Eledon Pharmaceuticals’ anti-CD40L antibody AT-1501, is one of the earliest widely reported examples: the “-bart” stem marks it as an engineered (Fc-modified) monospecific immunoglobulin, with “-pru-” signaling an immunosuppressive target [5]. Analysts illustrating the new logic against familiar drugs have noted that, applying the four-stem rules hypothetically, Merck and Pfizer’s avelumab would read as “aveprutug” (unmodified immunoglobulin, immunosuppressive target), Johnson & Johnson’s bispecific amivantamab would read as “amivantamig,” and Sanofi’s antibody fragment caplacizumab would read as “caplacment” — these are illustrative only and not official renamings, but they show how the four-stem logic reclassifies familiar drugs [6].
What This Means for Competitive Intelligence Going Forward
For pipeline monitoring, the practical consequence is that “-mab” can no longer be used as a search filter to catch new antibody candidates in WHO Drug Information listings — new entries will carry one of the four replacement stems instead, and a stem-based monitoring workflow built before 2022 will silently miss them unless it is updated. The reform also means that a drug’s stem now discloses more about its molecular engineering (unmodified versus artificially modified constant regions) than it does about species origin, which is a materially different piece of competitive information than the pre-2021 system provided.
Case Study: A Naming Break in the GLP-1 Class
The “-glutide” stem reliably marks peptide-based GLP-1 receptor agonists — semaglutide, liraglutide, dulaglutide. Eli Lilly’s orforglipron breaks that pattern deliberately. It is a non-peptide, orally bioavailable small molecule that activates the GLP-1 receptor through an entirely different chemical scaffold than the injectable peptide agonists [7], and its INN carries the “-glipron” ending rather than “-glutide,” visibly signaling to anyone reading the stem that this is not a peptide despite sharing the drug class and target. Phase 3 data (ATTAIN-1) reported 11.2% mean weight loss at 72 weeks against 2.1% for placebo across 3,127 adults with obesity, and as of the most recent public reporting the compound remained investigational, with an NDA submission expected and a decision pending [8]. For analysts running stem-based searches, orforglipron is a reminder that a new mechanism or delivery route inside an existing pharmacological class can force a naming split — the stem tracks structural chemistry as much as it tracks receptor target, and the two don’t always move together.
Biosimilar Naming: The FDA Suffix Policy Has Changed Twice Since 2017
The 2017 Rule, Briefly Restated
The FDA finalized its four-letter distinguishing suffix policy for biosimilars and their reference products in 2017. Adalimumab biosimilars carry suffixes such as “-adaz” (Hyrimoz), “-adbm” (Cyltezo), and “-atto” (Amjevita, the reference product’s own retroactively assigned suffix).
The 2024–2025 Reversal on Retroactive Suffixes
What the original 2017 policy did not anticipate, and what most naming explainers written before 2024 do not reflect, is that the FDA has since walked back part of it. In an updated draft guidance, the agency stated it no longer intends to retroactively apply four-letter suffixes to already-licensed biologics that were approved before the suffix policy existed [9]. The agency will still assign suffixes to newly approved innovator biologics, biosimilars, and interchangeable biosimilars going forward, and transition products such as insulins remain exempt from suffixing entirely [9]. Once a biosimilar is later determined interchangeable with its reference product, it keeps its original nonproprietary name and suffix rather than receiving a new one [9].
“The US is the only country to adopt a suffix for biologics and biosimilars.” [10]
Why Industry Keeps Pushing Back
The comment period on the FDA’s updated draft guidance closed with continued opposition from multiple directions. The United States Pharmacopeia supported the decision not to retroactively suffix already-approved products but said it remained concerned about unintended consequences of continuing to suffix new approvals [11]. Novartis and Sandoz argued that if the FDA proceeds with prospective suffixing, retroactive suffixes should be applied selectively to reference products of already-approved biosimilars and interchangeables to preserve internal consistency, while maintaining that suffixes generally are “not warranted nor desirable” [11]. The Biologics Prescribers Collaborative, a group that generally supports the FDA’s broader Biosimilar Action Plan, specifically asked the agency to make suffixes memorable rather than randomly generated and devoid of meaning [12]. The FDA’s own restated position across this guidance cycle has been to keep the suffix requirement for all future approvals while setting a high evidentiary bar for interchangeability designations [10].
Practical Implication for Purple Book and BPCIA Tracking
For patent and regulatory analysts, the retreat from retroactive suffixing means that a meaningful share of pre-2017 biologics in the Purple Book will permanently carry no distinguishing suffix at all, while every biosimilar and interchangeable approved from 2017 forward will. That asymmetry has to be built into any automated Purple Book query logic — assuming every biologic in the database follows a base-INN-plus-suffix pattern will silently drop the oldest reference products from a suffix-based search.
The Architecture of the INN and USAN System
Chemical Names, Brand Names, and the Case for a Third Name
Every drug in clinical use carries at least three names. The IUPAC chemical name for atorvastatin describes the molecule with complete precision and is unusable in a clinical setting. The brand name is a marketing construct, legally trademarked and deliberately disconnected from pharmacology in most cases. The generic, or nonproprietary, name sits between the two: pronounceable, class-specific, and owned by no single company.
Who Assigns the Name: WHO, USAN, and National Bodies
The WHO’s INN Programme, established in 1950, has assigned nonproprietary names to a body of pharmaceutical substances that by 2016 already numbered over 8,000 [13], and has grown considerably since. In the United States, the USAN Council — a joint body of the American Medical Association, the U.S. Pharmacopeial Convention, and the American Pharmacists Association, with the FDA as a cooperating agency — assigns the operative U.S. name. INN and USAN are coordinated closely enough that the two are usually identical, but legacy divergences persist: paracetamol (INN/BAN) versus acetaminophen (USAN), adrenaline versus epinephrine, frusemide versus furosemide, lignocaine versus lidocaine.
The INN Application Timeline
A company typically files its INN application roughly 18 months ahead of the anticipated regulatory filing. The WHO Secretariat proposes a Recommended INN (rINN), publishes it in WHO Drug Information for a four-month public comment window, and finalizes the name after resolving any objections — most commonly phonetic collisions with existing names, trademark conflicts, or structural errors in the proposed stem.
Stem Reference by Therapeutic Category
The WHO’s consolidated stem list runs past 400 entries. The table below groups the stems that appear most often in active patent and competitive-intelligence work.
Category
Stem
Class
Representative drugs
Cardiovascular
-olol
Beta-adrenoreceptor antagonists
propranolol, atenolol, metoprolol
Cardiovascular
-pril
ACE inhibitors
captopril, enalapril, lisinopril
Cardiovascular
-sartan
Angiotensin II receptor blockers
losartan, valsartan, irbesartan
Cardiovascular
-vastatin
HMG-CoA reductase inhibitors
atorvastatin, rosuvastatin, simvastatin
Metabolic
-gliflozin
SGLT2 inhibitors
empagliflozin, dapagliflozin, canagliflozin
Metabolic
-glutide
Peptide GLP-1 receptor agonists
semaglutide, liraglutide, dulaglutide
Metabolic (new)
-glipron
Non-peptide, orally active GLP-1 receptor agonists
orforglipron
Oncology
-tinib
Kinase inhibitors (broad)
imatinib, osimertinib, sunitinib
Oncology
-ciclib
CDK4/6 inhibitors
palbociclib, ribociclib, abemaciclib
Oncology
-parib
PARP inhibitors
olaparib, niraparib, rucaparib
CNS
-gepant
CGRP receptor antagonists
rimegepant, ubrogepant, atogepant
Biologics (legacy, pre-2022)
-mab
Monoclonal antibodies (all formats)
adalimumab, pembrolizumab, trastuzumab
Biologics (current)
-tug
Unmodified full-length immunoglobulins
compounds named 2022 onward
Biologics (current)
-bart
Fc-engineered immunoglobulins
tegoprubart
Biologics (current)
-mig
Bispecific/multispecific immunoglobulins
compounds named 2022 onward
Biologics (current)
-ment
Antibody fragments without full Fc
compounds named 2022 onward
Cell therapy
-cel
CAR-T cell therapies
axicabtagene ciloleucel, tisagenlecleucel
Generic Naming and Patent Prior Art: Timing Matters
Why the INN Publication Date Is a Legal Event
An INN designation is a public disclosure. Once a compound’s pharmacological class is disclosed through its stem — even without a full structural description — it can function as prior art against a later-filed patent application claiming a genus that includes it, under 35 U.S.C. § 102. The sequencing question is strategic: filing a patent application before submitting the INN application preserves priority date protection against a subsequent INN-based disclosure argument. Filing the INN application first can create prosecution complications that need to be addressed head-on rather than discovered during examination.
Salt and Ester Forms: Modified INNs
A Modified INN (INNM) attaches a salt, ester, or prodrug descriptor to the base INN — enalapril becomes enalapril maleate; amlodipine becomes amlodipine besylate. This distinction has litigated consequences: a compound patent covering a free base does not automatically cover every salt form, and Paragraph IV disputes have turned on whether a specific salt form falls inside claim scope drafted around a different salt or the free base. Abbott Laboratories v. Andrx Pharmaceuticals, 452 F.3d 1331 (Fed. Cir. 2006), is a reference point for how salt-form claim construction has played out in practice.
Naming and Medication Safety
The ISMP Confused Name List and FDA’s POCA Review
The Institute for Safe Medication Practices maintains a running list of drug name pairs implicated in dispensing or administration errors, and the FDA’s Division of Medication Error Prevention and Analysis screens every proposed brand and generic name through its Phonetic and Orthographic Computer Analysis (POCA) system before approval, generating a list of existing names that are visually or phonetically close enough to create clinical confusion risk.
Tall Man Lettering as a Non-Naming Safety Layer
Tall man lettering — capitalizing the distinguishing portion of two similar names, as in vinBLAStine/vinCRIStine or hydrALAzine/hydrOXYzine — does not change the underlying INN or USAN. It is a labeling and electronic-prescribing convention layered on top of the name, and the FDA’s published list of recommended pairs functions as a de facto packaging standard that manufacturers building label and e-prescribing configurations need to track independently of the naming process itself.
Using Naming Data as a Competitive Intelligence Signal
Reading Proposed INN Lists Before Phase II Data Exists
WHO Drug Information publishes proposed INNs quarterly, typically during late preclinical or early clinical development — well before a brand name exists and often before Phase II results are public. A quarter that shows three new compounds carrying the same novel stem is a signal that at least three companies are running programs against the same mechanistic target, months or years ahead of a public pipeline announcement.
New Stem Registrations as an R&D Consensus Signal
The registration of a genuinely new stem — “-gepant” for CGRP antagonists in the mid-2010s, “-cel” for CAR-T therapies, “-degib” for hedgehog pathway inhibitors — indicates the WHO judged an emerging mechanism significant enough to require its own classification, which in practice means multiple sponsors already had compounds far enough along to need naming. The four-stem antibody reform belongs in the same category at a system-wide scale: it is the WHO’s acknowledgment that antibody engineering diversity (unmodified, Fc-engineered, multispecific, fragment) had become commercially important enough to require permanent, structural — not just species-based — classification.
FAQ
Does every monoclonal antibody named before 2022 need to be renamed under the new system? No. The four-stem reform applies prospectively only. Adalimumab, pembrolizumab, and every other antibody named before the scheme’s effective date keep their original “-mab” designation permanently; there is no renaming of legacy products [4].
What does the “-glipron” ending in orforglipron signal that “-glutide” does not? It marks the compound as a non-peptide, small-molecule GLP-1 receptor agonist rather than a peptide, which is the structural distinction that makes oral dosing without injection possible in the first place [8].
Will already-approved biologics like Humira eventually lose their retroactively assigned suffix? Humira’s reference-product suffix (adalimumab-atto) was already assigned under the original 2017 policy and remains in place. The FDA’s newer position is that it will not retroactively suffix biologics that were approved before the suffix policy existed and never received one, not that it will remove suffixes already assigned [9].
Is the four-letter biosimilar suffix used anywhere outside the United States? No major jurisdiction outside the U.S. uses this approach; other regulators, including Australia’s TGA, converged on giving biosimilars the same name as their reference product rather than a distinguishing suffix [10].
How many INN stem categories exist for monoclonal antibodies now? Four primary structural stems (-tug, -bart, -mig, -ment) replace the single “-mab” suffix, layered with a separate set of target/disease substems (including the newer -ki-, -ler-, -sto-, -pru- split of the old “-li-” category) that indicate the therapeutic target [3][4].
Can an INN alone serve as prior art in an IPR proceeding? It can support an obviousness or motivation-to-combine argument by establishing that a compound or its pharmacological class was publicly known before a patent’s filing date, but an INN listing rarely discloses enough structural detail to serve as a standalone anticipation reference under 35 U.S.C. § 102; it typically needs to be combined with other prior art providing structural and activity data.
Why did the WHO eliminate the human/humanized/chimeric distinction from antibody names? By the early 2020s antibody engineering had advanced to the point where the clinical significance of that distinction had diminished, and the naming space within each source-substem combination had become too crowded to keep generating distinguishable names — eliminating it freed capacity while the new stems captured a more clinically relevant distinction (unmodified versus engineered, monospecific versus multispecific).
Does a biosimilar’s four-letter suffix change if it is later approved as interchangeable? No. A product that is first approved as a biosimilar and later determined interchangeable with its reference product keeps its original nonproprietary name, suffix included [9].
Are transition products like insulins subject to the suffix requirement? No. The FDA’s updated guidance explicitly excludes transition products such as insulins from suffix assignment [9].
Where can I track new proposed INNs before they reach clinical trial registries? WHO Drug Information publishes proposed INN lists quarterly and is the earliest public naming-stage disclosure point, ahead of most ClinicalTrials.gov registrations for the same compound.
Key Takeaways
The WHO did not merely trim the pre-2021 antibody naming system — it eliminated “-mab” for new INNs entirely, replacing it with four structurally defined stems: -tug, -bart, -mig, and -ment [1][3].
879 antibodies already carried the “-mab” suffix by 2022, which is the capacity pressure that drove the reform [2].
Tegoprubart is an early real-world example of a compound named under the new four-stem system, combining “-bart” (Fc-engineered) with the “-pru-” immunosuppressive infix [5].
Orforglipron’s “-glipron” stem breaks from “-glutide” specifically to flag that it is a non-peptide, orally active GLP-1 receptor agonist rather than an injectable peptide [7][8].
The FDA’s biosimilar suffix policy changed materially in 2024–2025: retroactive suffixing of pre-2017 biologics is off the table, but prospective suffixing of all new biologic, biosimilar, and interchangeable approvals continues [9].
Industry stakeholders including USP, Novartis, and Sandoz continued pushing back on the suffix policy through the most recent comment period, with proposals ranging from memorable suffixes to selective retroactive application [11].
Legacy biologics that predate 2017 and were never retroactively suffixed will permanently lack a distinguishing suffix, creating an asymmetry that automated Purple Book queries need to account for.
INN publication is a legally material disclosure event for patent prior art purposes; the relative timing of INN application and patent filing is a strategic decision, not an administrative afterthought.
Sources
[1] Guimaraes Koch, S. S., Thorpe, R., Kawasaki, N., Lefranc, M-P., et al. (2022). International nonproprietary names for monoclonal antibodies: an evolving nomenclature system. mAbs, 14(1), 2075078. https://doi.org/10.1080/19420862.2022.2075078
[2] Guimaraes Koch, S. S., et al. (2022). Ibid. (879-antibody figure).
[3] World Health Organization. (2022). New INN monoclonal antibody (mAb) nomenclature scheme. WHO Working Document INN 22-542. https://www.who.int/publications/m/item/inn-22-542
[4] Blopig. (2022). New Antibody Therapeutic INNs will no longer end in “-mab”! https://www.blopig.com/blog/?p=7705
[6] Culturaldaily.com summary of the WHO four-stem antibody naming reform with illustrative examples. https://www.culturaldaily.com/author/echosmith888
[7] Eli Lilly and Company / Cayman Chemical. Orforglipron product description (nonpeptide GLP-1 receptor agonist). https://cdn.caymanchem.com/cdn/insert/39741.pdf
[8] Superpower Health. Orforglipron: A Non-Peptide Oral GLP-1 Receptor Agonist in Clinical Development. https://superpower.com/guides/orforglipron
[9] Center for Biosimilars. FDA releases guidance on biologic, biosimilar, and interchangeable biosimilar naming conventions. https://www.centerforbiosimilars.com/news/fda-releases-guidance-on-biologic-biosimilar-and-interchangeable-biosimilar-naming-conventions
[10] Biotech Dispatch. FDA sticks with ‘suffix’ and sets a high bar for interchangeability. https://biotechdispatch.com.au/news/fda-sticks-with-suffix-and-sets-a-high-bar-for-interchangeabilit
[11] Center for Biosimilars. In comment letters, stakeholders call on FDA to change course on biosimilar naming. https://centerforbiosimilars.com/view/in-comment-letters-stakeholders-call-on-fda-to-change-course-on-biosimilar-naming
[12] Center for Biosimilars. Biologics Prescribers Collaborative calls on FDA to address interchangeability suffixes. https://www.centerforbiosimilars.com/news/biologics-prescribers-collaborative-calls-on-fda-to-address-interchangeability-suffixes
[13] Institute for Safe Medication Practices research cited in: Patient Safety in Medication Nomenclature: Orthographic and Semantic Properties of International Nonproprietary Names. PMC. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4689353/
