Authors: Faith White, Ah Lim Yoo, Erin Pace Background: Insulin glargine-yfgn (Semglee) is a recently approved interchangeable biosimilar to insulin glargine. Comparable cost and clinical efficacy between insulin glargine-yfgn and NPH insulin (Humulin N) prompted institution-wide conversion from its preferred basal insulin NPH to insulin glargine-yfgn. However, there is currently limited guidance regarding the conversion between insulin glargine-yfgn and other insulins due to recent approval. As a result, prescribing information for insulin glargine was utilized to guide the conversion initiative. This prompted either a 1:1 conversion for patients taking up to 50 units of NPH daily or a reduction in NPH total daily dose (TDD) by 20% for patients taking greater than 50 units daily or NPH twice daily. Therefore, this project aims to address the knowledge gap in conversion methods between NPH and insulin glargine-yfgn by evaluating real-world data in an outpatient setting, specifically TDD and changes in glycated hemoglobin (A1c) before and after conversion. Methods: This retrospective cohort study was designed to assess conversion methods from NPH to insulin glargine-yfgn within outpatient clinics throughout the study institution. The conversion date was defined as the initial fill date of the first insulin glargine-yfgn order following previous NPH orders. Demographic variables, A1c, and TDD values were collected from an electronic health record. A1c values were collected at baseline (within 6 months prior to conversion) and approximately 6 months after conversion. TDD of NPH was collected at baseline, TDD of insulin glargine-yfgn on the date of conversion, and TDD of insulin glargine-yfgn approximately 6 months after conversion. Inclusion criteria were age greater than or equal to 18 years, type 1 or 2 diabetes, and conversion from NPH to insulin glargine-yfgn between April 1, 2024 and April 1, 2025. Exclusion criteria were concurrent therapy with other insulins (e.g. short acting, rapid acting, premixed formulations), pregnancy, prediabetes diagnosis, titrate-to-target dosing, and discontinuation of insulin glargine-yfgn within 6 months from conversion. The primary outcome was the mean change in TDD of NPH from baseline to the TDD of insulin glargine-yfgn 6 months after conversion. The secondary outcome was the mean change in A1c from baseline to 6 months after conversion. A Wilcoxon Signed Rank test was completed to analyze the TDD and A1c variables among the included participants. Results: Of the 1,245 eligible individuals that were screened, a total of 892 patients were included in this study. The majority of the study population were African American (54%), female (53%), and mean age of 65 years. Type 2 diabetes (99.7%) was the more commonly observed diagnosis. The mean TDD of insulin prior to conversion was 43.5 units compared to 38.6 units approximately 6 months after conversion. This indicates a statistically significant reduction in mean TDD by 4.88 units (p < 0.0001). Additionally, there was a statistically significant reduction in A1c by 0.08% (p = 0.0204) from 8.13% prior to conversion to 8.05% after conversion. Conclusion: The transition from NPH to insulin glargine-yfgn yielded a slight decrease in TDD and A1c. While the approximate 10% decrease in TDD may be interpreted as clinically significant in some scenarios, the overall A1c reduction was minimal. Current conversion guidance may not provide substantial benefit in A1c control partially due to the recommendations for preemptive insulin dose reduction for safety purposes. However, it may be reasonable to consider an initial 1:1 conversion in appropriate circumstances to provide additional A1c lowering. Such instances may be patients with elevated A1C and those who have not experienced hypoglycemia with the original TDD prior to the conversion.
