The short answer is “YES.” If a sponsor is submitting a brand name to the U.S. Food and Drug Administration (FDA) for an originator biological product, related biological product, or biosimilar product, then a four-letter distinguishing suffix (i.e., -xxxx) should be added to the core name or the nonproprietary name.
For over a decade, Brandsymbol, a leading creative agency, has developed a methodology called the SafeMark Model 4-letter suffixes to help sponsors develop, evaluate, and select up to 10 distinguishing suffixes for the FDA to review as part of the biologic brand name review process. In 2025, we are gradually transitioning our phrasing from “four-letter suffix” to “distinguishing suffix” to anticipate that, in the future, four-character positions may be too limited due to the growing number of newly approved medicines in this category.
In the simplest terms, the purpose of a four-letter suffix is to distinguish products that contain the same nonproprietary name but are not interchangeable.
Below are eight examples of proper names that include “trastuzumab” as the nonproprietary name, along with a distinguishing suffix identifier as designated by the FDA (Source: FDA CBER Purple Book). These examples highlight the importance of a well-structured biosimilar suffix naming process to ensure FDA compliance.
- Herceptin Hylecta (trastuzumab and hyaluronidase-oysk)
- Hercessi (trastuzumab-strf)
- Herzuma (trastuzumab-pkrb)
- Kanjinti (trastuzumab-anns)
- Ogivri (trastuzumab-dkst)
- Ontruzant (trastuzumab-dttb)
- Phesgo (pertuzumab, trastuzumab, and hyaluronidase-zzxf)
- Trazimera (trastuzumab-qyyp)
Both originator products and biosimilars currently require this naming convention, which, according to the FDA, is designed “to facilitate pharmacovigilance for originator biological products, related biological products, and biosimilar products containing related drug substances when other means to track a specific dispensed product are not readily accessible or available.”
In addition to the brand name, the distinguishing suffix can help minimize “inadvertent substitution of any such products that have not been determined to be interchangeable.” However, a suffix is not required for “certain categories of biological products for which there are well-established, robust identification and tracking systems to ensure safe dispensing practices and optimal pharmacovigilance,” such as autologous products and childhood vaccines.
When evaluating a distinguishing suffix, consider how it will be used in practice among healthcare professionals in common medical processes such as ordering, prescribing, dispensing, and recording medications.
Per the FDA’s guidance, applicants may include a prioritized list of 10 proposed distinguishing suffixes, in order of preference, during the Investigational New Drug (IND) application phase or at the time of Biologics License Application (BLA) submission.
| A proposed Distinguishing Suffix should be… |
A proposed Distinguishing Suffix should not be… |
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The FDA will assign a distinguishing suffix as part of the proper name (core or nonproprietary name + distinguishing suffix) if none are submitted or deemed acceptable.
If you need expert guidance on FDA biosimilar naming requirements or biologic drug name approval, our team is here to help.