Initiation of the Interchangeable Biosimilar Insulin Glargine-yfgn Among Older Adults

ABSTRACT

Objective: The approval of the biosimilar insulin glargine-yfgn presents a cost-effective alternative for diabetes management. This study assessed insulin glargine-yfgn initiation among older adults using insulin glargine in Pennsylvania.

Study Design: This retrospective cohort study included insulin glargine users 65 years and older who were enrolled in Pennsylvania’s Pharmaceutical Assistance Contract for the Elderly program from July 1, 2021, to June 30, 2023.

Methods: The primary exposure variable, prior insulin glargine use between July 1 and December 31, 2021, was classified into 5 categories: no use, Lantus alone, Basaglar alone, Toujeo alone, and multiple insulin glargine types. The main outcome, insulin glargine-yfgn initiation, was classified based on having at least 1 insulin glargine-yfgn (branded Semglee or unbranded version) prescription between January 1, 2022, and June 30, 2023. Chi-square tests and multivariate logistic regression were used to examine factors associated with insulin glargine-yfgn initiation.

Results: Among 6866 patients, 3.7% initiated insulin glargine-yfgn. Insulin glargine-yfgn initiators were less likely than noninitiators to have previously used Lantus, Basaglar, or Toujeo. They were more likely to reside in rural counties (adjusted OR [AOR], 1.39; P = .0135), be in long-term care facilities (AOR, 2.10; P = .0069), and have multiple prescribers (≥ 3 prescribers: AOR, 3.23; P < .0001) compared with noninitiators. Only 1.6% of insulin glargine prescriptions were for insulin glargine-yfgn, with relatively more prescriptions filled at nursing home pharmacies and written by physicians.

Conclusions: Insulin glargine-yfgn use among older adults is low despite its cost-effectiveness. Overcoming barriers related to prescribing patterns, formulary placement and reimbursement challenges, and pharmacy channels could improve insulin glargine-yfgn adoption, reducing diabetes care costs.

Am J Manag Care. 2026;32(4):e126-e132. https://doi.org/10.37765/ajmc.2026.89925

Takeaway Points

Initiation of biosimilar insulin glargine-yfgn among older adults in Pennsylvania was low (3.7%) despite its cost-effectiveness. Insulin glargine-yfgn initiators were more likely to reside in rural areas, live in long-term care facilities, or have multiple prescribers, and they were less likely to have used an originator insulin glargine (Lantus, Basaglar, or Toujeo) previously. To improve biosimilar adoption, strategies should include the following:

• expand formulary access to lower costs;
• streamline reimbursement policies;
• increase availability in nursing homes and rural pharmacies; and
• provide targeted education to prescribers, pharmacists, and patients.

These efforts can promote broader biosimilar uptake and help reduce overall diabetes care costs.

Diabetes is a prevalent chronic condition and a growing public health challenge in the 21st century. In 2021, nearly 30% of individuals 65 years and older were diagnosed with diabetes,¹ underscoring the high burden of this disease. Spending on diabetes care among older adults has surged, with approximately 67% of diabetes-related health care expenditures in 2022 directed toward this group,² up from 61% in 2017.³

Insulin remains a cornerstone of diabetes treatment and is widely prescribed for type 1 and advanced or uncontrolled type 2 diabetes; however, it carries a significant cost burden. In 2022, the US national insulin expenditure reached $22.3 billion, with prices increasing by up to 179% between 2012 and 2022.^2,4 The high cost of insulin affects patients of all ages, especially older adults, many of whom may face limited financial resources.^1,2 As a result, some delay or forgo insulin prescriptions,⁵ increasing the risk of kidney disease, vision loss, ketoacidosis, and other serious complications.⁶

Among insulin products, insulin glargine, a long-acting insulin analog, ranked as the third-highest drug by expenditure in 2020 at $9.7 billion.⁷ To address affordability, biosimilar insulins have emerged as a promising avenue. In July 2021, the FDA approved insulin glargine-yfgn (Semglee) as the first interchangeable biosimilar to insulin glargine (Lantus); it launched in 2 versions later that year: branded Semglee, priced slightly below Lantus, and an unbranded insulin glargine-yfgn, priced 65% lower.⁸ Following the interchangeable designation, utilization of both versions rose substantially, with unbranded insulin glargine-yfgn showing higher initial uptake and greater peak utilization.⁹ The increase occurred across all dispensing channels—retail, mail order, and long-term care (LTC)—with retail and LTC settings showing particularly strong uptake.⁹ Consistent with the LTC findings, Hayes et al reported increased insulin glargine biosimilar adoption among US nursing home residents from June to November 2021.¹⁰ Although the biosimilar’s uptake may have been influenced by favorable formulary placement, insulin glargine-yfgn grew rapidly in Medicare Part D, Medicaid, and cash markets, suggesting the interchangeable designation alone contributed to its growth.⁹

To further address insulin affordability, federal policy introduced key reforms. The Part D Senior Savings Model (SSM), launched in 2021, tested a $35 monthly cap on costs of select insulins for Medicare beneficiaries, with no deductible applied.¹¹ Building on this model, the Inflation Reduction Act (IRA) made this cap permanent—limiting out-of-pocket insulin costs to $35 per month under Medicare Part D starting January 2023 and under Part B beginning July 2023.¹² Additionally, Sanofi announced a 78% price reduction for Lantus, effective January 2024.¹³ Together, biosimilar adoption and policy reforms contributed to insulin glargine’s drop in national drug spending—falling to 13th place in 2023, with expenditures reduced to $8.89 billion.¹⁴

Despite this progress, barriers to biosimilar adoption persist. Between January 2021 and March 2023, Lantus maintained a 78% market share across all payer channels.¹⁵ Although unbranded insulin glargine-yfgn gained a 31% market share in Medicare by March 2022, Semglee accounted for only 6%.¹⁵ Uptake remained slowest in Medicare Part D, where limited coverage continued to hinder access. Although demand (new patient written share) for unbranded insulin glargine-yfgn rose from 25% to 49% between quarter 1 (Q1) of 2022 and Q1 2023, only 34% of Medicare patients prescribed Semglee and 19% prescribed unbranded insulin glargine-yfgn filled their prescriptions in Q1 2023.¹⁵

Understanding the need for cost-effective diabetes treatment, we examined initiation of insulin glargine-yfgn (branded Semglee and unbranded insulin glargine-yfgn) among older adults in Pennsylvania using insulin glargine. We also identified patient and provider characteristics to inform efforts that support this biosimilar’s appropriate use and integration into diabetes care.

METHODS

This study used a retrospective cohort design using a sample of adults 65 years and older enrolled in Pennsylvania’s Pharmaceutical Assistance Contract for the Elderly (PA-PACE) program. Eligible participants were continuously enrolled from July 1, 2021, to June 30, 2023, and had at least 1 prescription claim for insulin glargine (Lantus, Basaglar, Toujeo, Semglee, or unbranded insulin glargine-yfgn) between January 1, 2022, and June 30, 2023. PA-PACE is a state-funded program administered by the Pennsylvania Department of Aging that helps income-eligible residents 65 years and older cover prescription medication costs.¹⁶ Further details are available elsewhere.¹⁶

All insulin glargine claims—including all available strengths and formulations—submitted to PA-PACE between July 1, 2021, and June 30, 2023, were included in the analysis (Table 1). Individuals with any branded Semglee or unbranded insulin glargine-yfgn claims during the baseline period (7/1/2021-12/31/2021) were excluded (n = 12) to clearly assess biosimilar initiation during the follow-up period (1/1/2022-6/30/2023). The final analytic sample consisted of 6866 patients. The study protocol received approval from the WCG Institutional Review Board.

Multiple data sets were integrated for this study, including pharmacy dispensing claims data, prescription drug attributes, and PA-PACE eligibility and demographic data.

Exposure Variable

The baseline period (7/1/2021-12/31/2021) was used to assess the primary exposure variable, prior insulin glargine use, categorized as (1) no use, (2) Lantus alone, (3) Basaglar alone, (4) Toujeo alone, and (5) multiple glargine products. This fixed 6-month baseline was selected to allow consistent covariate measurement across the cohort.

Outcome Variable

The primary outcome, insulin glargine-yfgn initiation, was defined as having at least 1 claim for branded Semglee or unbranded insulin glargine-yfgn during the follow-up period (1/1/2022-6/30/2023). Patients with no such claims were considered noninitiators.

Covariates

Covariates were measured as of January 1, 2022, and included age (categorized as 65-69, 70-74, 75-79, 80-84, or ≥ 85 years), sex (female or male), race (Black, White, or other), residence status (LTC or non-LTC), rurality (rural or urban, based on the Center for Rural Pennsylvania definitions¹⁷), marital status (single/widowed, married, or married but living separately/divorced), PA-PACE subgroup (PA-PACE or PACE Needs Enhancement Tier [PACENET]), and number of insulin glargine prescribers during follow-up (1, 2, or ≥ 3). LTC residence was defined by having at least 50% of claims from an LTC facility or documented nursing home/personal care residence during the baseline period. PA-PACE and PACENET differ by benefit structure and eligibility income thresholds. During the baseline period, the income limits for PA-PACE enrollment were $14,500 for single persons and $17,700 for married couples, whereas those for PACENET enrollment were $27,500 for single persons and $35,500 for married couples.¹⁶

Further, we categorized insulin glargine providers and prescribers based on dispensing or prescribing records (including new prescriptions and refills) during the follow-up period. Pharmacies were classified into independent, chain, nursing home, or other (institutional/mail order). Prescribers were grouped based on their professional licenses into physicians, physician assistants, nurse practitioners, or resident/unknown.

Statistical Analyses

Descriptive statistics of insulin glargine-yfgn initiators between January 1, 2022, and June 30, 2023, were reported using χ² tests and Fisher exact tests, with statistical significance set at a P value less than .05. We performed a multivariate logistic regression analysis to identify factors associated with insulin glargine-yfgn initiation. Adjusted ORs (AORs) with 95% CIs were reported. Additionally, provider and prescriber characteristics associated with insulin glargine-yfgn pharmacy claims were analyzed using χ² tests, with a significance level of less than .05. All statistical analyses were performed using SAS Enterprise Guide 8.4 (SAS Institute Inc).

RESULTS

Table 2 presents descriptive statistics of variables by insulin glargine-yfgn initiation. Among 6866 patients, only 3.7% (n = 254) initiated insulin glargine-yfgn during the follow-up period, with the first observed utilization on December 3, 2021. When further stratified by product, 71 individuals initiated branded Semglee, 195 initiated unbranded insulin glargine-yfgn, and 12 used both. Of the insulin glargine-yfgn (branded Semglee and unbranded version) initiators, 0.8% initiated in the first half of 2022, and 11.0% and 88.2% initiated in the second half of 2022 and the first half of 2023, respectively. Fisher exact test results indicated that prior insulin glargine use during baseline was significantly associated with insulin glargine-yfgn initiation (P < .0001).

Chi-square tests further demonstrated significant associations between insulin glargine-yfgn initiation and variables such as residence (P = .0010), rurality (P = .0077), and number of prescribers (P < .0001). Insulin glargine-yfgn initiators were more likely to reside in LTC facilities (6.7% vs 3.0%), live in rural areas (52.8% vs 44.3%), and have 2 or more prescribers (46.5% vs 31.8%) compared with noninitiators (Table 2).

Multivariate logistic regression analysis showed that compared with noninitiators, insulin glargine-yfgn initiators were less likely to have used Lantus (AOR, 0.59; 95% CI, 0.45-0.78; P = .0002), Basaglar (AOR, 0.22; 95% CI, 0.14-0.36; P < .0001), or Toujeo (AOR, 0.05; 95% CI, 0.01-0.19; P < .0001) alone. Furthermore, insulin glargine-yfgn initiators were more likely to reside in LTC facilities (AOR, 2.10; 95% CI, 1.23-3.59; P = .0069), live in rural counties (AOR, 1.39; 95% CI, 1.07-1.81; P = .0135), and have multiple prescribers (2 prescribers: AOR, 1.80; 95% CI, 1.34-2.40; P < .0001; ≥ 3 prescribers: AOR, 3.23; 95% CI, 2.21-4.72; P < .0001) compared with noninitiators (Table 3). The logistic regression model showed an acceptable fit with pseudo R² of 0.0210, Akaike information criterion of 2065.8, and –2 log likelihood of 2027.98. The Hosmer-Lemeshow test was nonsignificant (P = .4037), indicating good model calibration.

Overall, there were 59,028 claims for insulin glargine during the follow-up period, of which only 1.6% (n = 959) were filled for insulin glargine-yfgn. Insulin glargine-yfgn prescriptions were less likely to be dispensed by chain pharmacies (44.5% vs 63.4%; P < .0001) and prescribed by nurse practitioners (11.3% vs 15.3%; P = .0032) but were more likely to be dispensed by nursing home pharmacies (28.2% vs 8.0%; P < .0001) and prescribed by physicians (79.3% vs 74.4%; P = .0032) compared with non–insulin glargine-yfgn (Lantus, Basaglar, or Toujeo) prescriptions (Table 4).

DISCUSSION

This study is the first to examine patient and provider characteristics associated with initiation of insulin glargine-yfgn among older adults in Pennsylvania. Following the FDA approval of insulin glargine-yfgn as an interchangeable biosimilar, previous national analyses reported a sharp rise in utilization of both versions, with unbranded insulin glargine-yfgn showing higher initial and peak uptake across dispensing channels—particularly in retail and LTC settings.⁹ Semglee’s Medicare market share rose from 3% to 6% and unbranded insulin glargine-yfgn’s from 6% to 31% between Q1 2022 and Q1 2023.¹⁵ In our cohort, uptake was limited: Only 3.7% of patients initiated insulin glargine-yfgn between January 2022 and June 2023, with more patients initiating the unbranded version.

Our analysis identified several factors associated with insulin glargine-yfgn initiation: rural residence, LTC stay, multiple prescribers, and prior insulin glargine utilization. Insulin glargine-yfgn initiators were twice as likely to be in LTC compared with noninitiators, with a substantial number of prescriptions dispensed through nursing home pharmacies among PA-PACE participants. Consistent with our findings, Hayes et al reported rising biosimilar insulin glargine use in US nursing homes from June to November 2021.¹⁰ Another study found that uptake increased across all dispensing channels, with particularly strong growth in retail and LTC settings.⁹ Biosimilar use may be encouraged in postacute skilled nursing settings, where Medicare Part A’s bundled payments cover medications and incentivize lower-cost alternatives.¹⁰

We also conducted a subanalysis among branded Semglee and unbranded insulin glargine-yfgn initiators using separate multivariate models. Branded Semglee users were less likely to have used Basaglar alone, whereas unbranded insulin glargine-yfgn users were more likely to reside in LTC, live inrural areas, and have multiple prescribers and were less likely to have previously used Lantus, Basaglar, or Toujeo. However, these findings should be interpreted with caution due to the small sample sizes. Notably, our findings from the combined model were largely driven by the larger number of unbranded insulin glargine initiators.

Our finding that insulin glargine-yfgn initiation was more common in rural than urban areas contrasts with results of a prior study on biosimilar filgrastim adoption, where rural and 340B Drug Pricing Program–participating hospitals were less likely to adopt biosimilars, potentially due to formulary and reimbursement challenges.¹⁸ This discrepancy may reflect differences in prescribing practices, drug distribution channels, and reimbursement structures specific to long-acting insulin in outpatient settings. Further research is needed to understand the factors driving higher biosimilar uptake in rural areas and whether similar patterns exist for other biosimilar products.

Prior use of branded insulin glargine products was significantly associated with lower odds of insulin glargine-yfgn initiation. Compared with patients without prior insulin glargine use, those using Lantus only, Basaglar only, and Toujeo only had 41%, 78%, and 95% lower odds, respectively, of initiating insulin glargine-yfgn. This aligns with literature showing a preference for prescribing biosimilars to treatment-naive patients rather than switching stable patients from the originator biologic.¹⁹ Our findings that insulin glargine-yfgn initiators were less likely to have previously used Lantus, Basaglar, or Toujeo were consistent with existing evidence. Firstly, prescribers and patients may prefer to continue well-established options such as Lantus and Basaglar rather than switch to a newer biosimilar, particularly if diabetes is well controlled.^20,21 Toujeo, a higher-concentration formulation from the same manufacturer as Lantus, is often used by patients requiring enhanced glycemic control with fewer injections^22,23—a feature that insulin glargine-yfgn does not offer. It may also benefit from formulary placement advantages compared with insulin glargine-yfgn. Secondly, patients on reference products may exhibit stronger brand loyalty, perceiving them as more trustworthy, familiar, and effective than newer biosimilars.²⁴ This reluctance to switch could stem from both patient preference and provider prescribing behaviors; however, findings of a study on biosimilar filgrastim adoption suggested providers play a key role by predominantly prescribing either the biosimilar or reference product for all patients, leaving little room for patient choice.²⁵ Thirdly, formulary placement and rebate incentives present additional barriers to biosimilar adoption. Although Semglee and unbranded insulin glargine-yfgn are priced lower than Lantus, only 34% of Semglee and 19% of unbranded insulin glargine-yfgn prescriptions were filled in Q1 2023.¹⁵ These low fill rates highlight continued access challenges, particularly in Medicare Part D. The current rebate-driven formulary system allows manufacturers to offer substantial rebates to payers and pharmacy benefit managers (PBMs) in exchange for preferred placement. These confidential rebates may reduce net costs for originators like Lantus below those of biosimilars, discouraging biosimilar coverage—even when list prices are lower. This dynamic creates financial disincentive for switching and undermines efforts to reduce insulin spending. To improve insulin affordability, policy changes—the SSM and the IRA’s $35 monthly insulin cap for Medicare Part D beneficiaries—have been implemented to lower out-of-pocket costs.^11,12 Although these policy reforms may have contributed to the decline in national insulin glargine spending in 2023,¹⁴ further research is needed to assess their impact on biosimilar utilization among the Medicare population.

We also observed that insulin glargine-yfgn prescriptions were more likely to be written by physicians and less likely to be written by nurse practitioners. Physicians, particularly primary care doctors and endocrinologists, may have greater prescribing authority and awareness of biosimilars. Insulin glargine-yfgn initiators also had multiple prescribers, possibly reflecting more complex medical needs and greater specialist involvement. Further, chain pharmacies were less likely to dispense insulin glargine-yfgn, possibly due to agreements with PBMs or concerns about stocking lower-demand biosimilars.²⁶ Additionally, although pharmacists in all states are allowed to substitute reference products with interchangeable biosimilars without physician approval, most states have varying laws requiring notification to both prescriber and patient,^27,28 which can discourage active promotion of biosimilar substitutions. In Pennsylvania, pharmacists may substitute an interchangeable biologic unless the prescriber explicitly prohibits it verbally or in writing. They must notify the patient at dispensing, including the price difference, and inform the prescriber within 72 hours of the exact product and manufacturer dispensed.^29,30 Evidence suggests that state substitution laws influence the adoption of interchangeable biosimilars and that reducing such restrictions may help expand their use.³¹

Limitations and Strengths

This study has several limitations. First, insulin glargine use was determined using pharmacy dispensing claims data, which does not guarantee that patients took the medications as prescribed. Second, we were unable to determine whether the insulin glargine was prescribed for type 1 or type 2 diabetes, as the specific diagnosis was not available. The lack of information may impact the generalizability of our findings. Third, the results may not be broadly applicable to other populations because PA-PACE enrollees, on average, are older, have lower incomes, and include a higher proportion of women compared with the general US older adult population. Additionally, regional prescribing patterns, state-level formulary constraints, and socioeconomic factors unique to Pennsylvania may influence biosimilar adoption and introduce selection bias, further limiting external validity. Fourth, prescription data were limited to claims submitted to PA-PACE, where most enrollees also had Medicare Part D coverage during the study period. Because prescriptions billed primarily to Medicare Part D may not have been submitted as secondary claims to PA-PACE, some data might have been excluded. Moreover, the period for prior insulin glargine use was restricted from July through December 2021, so the potential influence of the exposure variable beyond this time frame on insulin glargine-yfgn initiation was not examined. Furthermore, the analysis did not account for the possibility that some individuals may have switched from one form of insulin glargine to another either before or after the defined baseline period. Finally, the use of a fixed baseline period may lead to exposure misclassification or fail to account for time-varying changes across the follow-up period. Although the model identified several significant predictors of insulin glargine-yfgn initiation, the pseudo R² value indicates limited explanatory power. This is expected in observational studies using claims data, where many influencing factors are not captured.

Despite these limitations, the study has several notable strengths. Using a retrospective cohort design allowed for evaluating the temporal relationship between influencing factors and insulin glargine-yfgn initiation, enhancing the validity of the findings. The study analyses included a large and diverse sample of older adults in Pennsylvania using insulin glargine and incorporated a broad range of variables. Additionally, the study leveraged point-of-sale pharmacy claims data to capture multiple insulin glargine products available on the market. As a state pharmacy assistance program, PA-PACE provides wraparound benefits to Medicare Part D and provides benefits for older adults not enrolled in Part D. This comprehensive approach provides valuable insights into factors associated with insulin glargine-yfgn adoption.

CONCLUSIONS

Our study provides critical insights into early insulin glargine-yfgn adoption among older adults, identifying key factors influencing initiation. Although insulin glargine-yfgn use remained modest, its increasing market share suggests growing acceptance in the Medicare population, particularly in LTC settings. Insulin glargine-yfgn initiators were more likely to reside in rural areas and LTC facilities and to have multiple prescribers, but less likely to have previously used Lantus, Basaglar, or Toujeo, reflecting potential patient and provider hesitancy to switch from established options. Additionally, factors such as formulary placement and reimbursement challenges may further restrict access to the biosimilar adoption. Addressing these challenges requires policy reforms, formulary updates, and stakeholder education to build trust in biosimilars. As biosimilars continue to evolve, ensuring access and promoting competition remain critical for optimizing cost savings and diabetes care.

Acknowledgments

The authors thank the Pennsylvania Department of Aging for its support in providing the data used in this study.

Author Affiliations: Prime Therapeutics LLC (SRK, DAH, LLL, ML), Harrisburg, PA; Bureau of Pharmaceutical Assistance, Pennsylvania Department of Aging (TVB), Harrisburg, PA.

Source of Funding: None.

Author Disclosures: The authors report no relationship or financial interest with any entity that would pose a conflict of interest with the subject matter of this article.

Authorship Information: Concept and design (SRK, DAH); acquisition of data (SRK, DAH, ML, TVB); analysis and interpretation of data (SRK, ML, LLL); drafting of the manuscript (SRK); critical revision of the manuscript for important intellectual content (SRK, DAH, LLL, ML); statistical analysis (SRK, DAH); administrative, technical, or logistic support (DAH, ML, TVB); content review on behalf of agency (TVB); supervision (DAH); and editorial support: manuscript editing and refinement (LLL).

Address Correspondence to: Shivani R. Khan, PhD, Prime Therapeutics LLC, 4000 Crums Mill Rd, Ste 303, Harrisburg, PA 17112. Email: shivani.khan@primetherapeutics.com.

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