Abstract

Background/Objectives: We described adverse event reporting patterns for insulin glargine marketed as 100 units/mL (Lantus), 300 units/mL (Toujeo), and 100 units/mL biosimilars (Basaglar/Semglee). Methods: We analyzed Food and Drug Administration Adverse Event Reporting System (FAERS) reports received from 2015 through 2025 that listed insulin glargine as a primary or secondary suspect. Reports were grouped by trade name into standard-strength originator (Lantus), high-strength (Toujeo), and biosimilar products. We defined a composite serious outcome (death, life-threatening event, hospitalization, or disability). Logistic regression adjusted for age, sex, reporter type, and year received; Firth’s penalized regression was used for sparse death and hospitalization outcomes. Sensitivity analyses restricted to reports without concomitant suspect products, overlapping calendar windows, and healthcare professional reports. Geographic reporting patterns were analyzed by country. Results: We included 43,905 eligible reports (Lantus: 35,927; Toujeo: 3699; biosimilars: 4279). Unadjusted death was highest for Lantus (8.2%) followed by biosimilars (6.0%) and Toujeo (3.2%). In the primary adjusted model (n = 28,519), reports listing Toujeo had lower adjusted reporting odds of the composite serious outcome compared with Lantus (aOR 0.88, 95% CI 0.81–0.96), while biosimilars showed higher odds (aOR 1.24, 95% CI 1.11–1.38). The biosimilar association was not robust: it attenuated without concomitant drugs (aOR 1.07, 95% CI 0.92–1.23) and reversed in healthcare professional reports (aOR 0.65, 95% CI 0.49–0.87). Device-related events were lower for biosimilars (aOR 0.58) and Toujeo (aOR 0.85). Geographic heterogeneity was extreme (Egypt 76.9% death vs. Italy 0.8%), and the US protective association reversed in recent years. Conclusions: After adjustment for report-level characteristics, Toujeo was associated with lower reporting odds of serious outcomes, while biosimilar findings were inconsistent across sensitivity analyses and driven by consumer reporting. Geographic heterogeneity and the Egypt outlier underscore the fragility of cross-country comparisons in spontaneous reporting data. These findings reflect reporting-behavior heterogeneity rather than differential product safety.

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