Analysis of Suffix Use for Biosimilar Product Identification in Postmarketing Adverse Event Reporting.

Accurate identification of medicines used in adverse event reports is crucial for effective postmarketing safety surveillance. The US Food and Drug Administration's (FDA) four-letter suffix naming convention was designed to facilitate accurate biological product identification, but the extent to which these suffixes have been incorporated into biosimilar reporting remains unclear. We conducted a cross-sectional analysis of US adverse event reports for all 72 FDA-approved biosimilar products in the FDA Adverse Event Monitoring System (AEMS) received through August 31, 2025, evaluating the proportion of reports containing a four-letter suffix, proprietary name, or other manufacturer identifiers. Of 24,711 reports analyzed, 12.7% (n = 3126) contained a biosimilar suffix, whereas 98.2% (n = 24,264) contained a proprietary name and 82% reported the manufacturer name. Suffixes served as the sole product identifier in only 1.7% (n = 413). These suffix-only reports were distinct: more frequently submitted directly to FDA (86.2% vs. 15.0%), by healthcare professionals (73.3% vs. 59.0%), commonly originated from Veterans Affairs Medical Centers and specialty pharmacies and involved more serious outcomes (47.7% vs. 27.9%), suggesting certain organizational preferences favoring nonproprietary name reporting. The product distribution also differed, with adalimumab-aacf most common in suffix-only reports (18.9%) vs. infliximab-dyyb overall (21.1%). Manufacturer information was present in 42.6% of suffix-only reports. These results suggest FDA's nonproprietary naming convention has achieved limited implementation for biosimilars in AEMS reporting practices, and other information present in AEMS reports may be sufficient for accurately identifying biosimilar products.