Lantus biosimilars and insulin glargine interchangeability guide: Semglee, Rezvoglar, Langlara pharmacy substitution, formulary exclusion risk, Part D coverage, and manufacturer support

Lantus (insulin glargine, Sanofi) was the first long-acting insulin analog approved in the US and remains one of the most widely prescribed diabetes medications. In 2021, Semglee (insulin glargine-yfgn) became the first biosimilar insulin to receive FDA interchangeability designation, allowing pharmacists in most states to substitute it for Lantus without prescriber approval.

Since then, Rezvoglar (insulin glargine-aglr, Eli Lilly) and Langlara (insulin glargine-aldy, Lannett/Sunshine Lake Pharma) have also received interchangeable status. Basaglar (insulin glargine, Eli Lilly) — a follow-on biologic approved under the 505(b)(2) pathway — has been on the market since 2016 but never received interchangeability designation.

Despite three interchangeable biosimilars, adoption has been slow. As of October 2025, interchangeable insulin glargine biosimilars accounted for only 13.7% of insulin glargine prescriptions, with Rezvoglar at just 0.8% of claims. Formulary positioning varies dramatically across PBMs, and exclusion risk is real: Basaglar was excluded from Express Scripts' 2025 formulary in favor of interchangeable biosimilars and branded alternatives.

This guide covers every FDA-approved insulin glargine product, interchangeability mechanics, state substitution laws, PBM formulary positioning, Part D implications, and manufacturer support programs for 2026.

Short answer

All FDA-approved insulin glargine products

Interchangeable biosimilars

Viatris/Biocon's dual-product strategy offers both a branded interchangeable (Semglee) and an unbranded interchangeable at a 65% discount to Lantus list price.

Follow-on biologic (505(b)(2))

Basaglar was approved under the 505(b)(2) pathway as a follow-on to Lantus, not as a 351(k) biosimilar. It cannot be substituted at the pharmacy without a new prescription.

Insulin glargine U-300 (not substitutable)

Toujeo (insulin glargine U-300, Sanofi) is a concentrated formulation that is a distinct product from Lantus (U-100). It is not substitutable with any U-100 insulin glargine product.

Interchangeability: what it means and how it works

FDA interchangeability designation

The FDA grants interchangeability status when a biosimilar manufacturer demonstrates that the product can be expected to produce the same clinical result as the reference product in any given patient, and that the risk of alternating or switching between the biosimilar and reference is not greater than the risk of using the reference alone.

Beginning in 2025, the FDA moved toward allowing biosimilar manufacturers to submit pharmacokinetic and pharmacodynamic data to demonstrate interchangeability rather than requiring switching studies in human subjects, reducing the evidentiary burden.

State pharmacy substitution laws

Interchangeability enables — but does not guarantee — automatic pharmacy substitution. State laws vary:

• Permissive substitution states (majority): Pharmacists may substitute an interchangeable biosimilar for the reference product without contacting the prescriber. Some states require pharmacists to notify the prescriber within a specified timeframe (e.g., 5 business days) and to record the product dispensed.
• Mandatory substitution states: Some states require pharmacists to dispense the interchangeable biosimilar if it is available and the prescription was written for the reference product, unless the prescriber has explicitly indicated "dispense as written" or "brand medically necessary."
• Patient notification: Many states require that the pharmacist inform the patient when a substitution is made.

The National Conference of State Legislatures tracks state biosimilar substitution laws, and access teams should verify the specific requirements in each state where they operate.

Why interchangeability matters for insulin specifically

Insulin glargine is dispensed almost exclusively through the pharmacy benefit, not the medical benefit. This makes pharmacy-level substitution the primary mechanism for biosimilar adoption, unlike physician-administered biologics where the prescriber controls product selection through buy-and-bill.

For insulin glargine, interchangeability means:

1. A pharmacist can switch a patient from Lantus to Semglee at the point of dispensing without calling the prescriber
2. Payers can design formularies that prefer interchangeable products and exclude the reference product
3. The patient may receive a different injection device (pen design), which can affect adherence

PBM formulary positioning: 2025–2026

Express Scripts (Cigna)

Express Scripts was an early adopter of interchangeable insulin glargine. In January 2022, Semglee was added to the Express Scripts National Preferred Formulary as a preferred biosimilar to Lantus. The formulary also includes Semglee in the Patient Assurance Program, which limits patient out-of-pocket costs.

For 2025, Express Scripts excluded Basaglar from the formulary, positioning interchangeable biosimilars and other long-acting insulins (Tresiba, Toujeo) as preferred alternatives. The 2026 Express Scripts formulary continues this trend:

• Lantus, Semglee (insulin glargine-yfgn), and insulin glargine unbranded are excluded from the National Preferred Formulary
• Preferred options include insulin glargine-yfgn by Civica and insulin glargine-yfgn by Biocon

Optum Rx (UnitedHealth Group)

Optum Rx has historically favored Lantus and Toujeo as preferred long-acting insulins. In 2021, OptumRx excluded Semglee from its Premium Formulary while placing it on Tier 3 with step therapy on the Select Formulary. This was a notable reversal of expectations — the interchangeable biosimilar was excluded while the reference product was preferred.

By 2026, OptumRx's formulary evolution reflects the broader market shift toward insulin affordability, but specific tier placement for interchangeable insulin glargine products should be verified on the current formulary documents.

CVS Caremark

Caremark's approach has evolved with the broader insulin market. Following the major manufacturers' 2024 list-price cuts for insulin products, the formulary dynamics shifted. Access teams should check current Caremark formulary documents for tier placement and any step-therapy requirements for interchangeable insulin glargine products.

Key takeaway for access teams

PBM formulary positioning for insulin glargine is inconsistent. An interchangeable biosimilar may be preferred on one PBM's formulary and excluded on another. This fragmentation means that manufacturer access teams cannot rely on interchangeability alone to drive adoption — formulary contracting remains essential.

Part D and Medicare implications

Part D coverage

All insulin glargine products are covered under Medicare Part D. The Inflation Reduction Act's $35 monthly cap on insulin cost-sharing (effective 2023) applies to all insulin products regardless of whether they are reference products or biosimilars.

2026 IRA negotiated drugs and insulin glargine

Insulin glargine products are not among the 10 drugs selected for CMS Medicare Drug Price Negotiation Program maximum fair prices (MFPs) in 2026. However, the broader insulin affordability provisions of the IRA (cost-sharing caps) continue to apply.

Formulary exclusion risk

The primary risk for branded insulin glargine products (Lantus, Basaglar) is formulary exclusion in favor of interchangeable biosimilars. Express Scripts' 2025 exclusion of Basaglar demonstrates that even products from major manufacturers are vulnerable when cheaper interchangeable alternatives exist.

For Semglee and Rezvoglar, the risk is inverted: their interchangeable status is an advantage on some formularies but a disadvantage on others where the reference product Lantus remains preferred due to rebate economics.

Adoption barriers

Despite three interchangeable biosimilars and clear cost advantages, adoption of interchangeable insulin glargine remains low. A 2026 study published in the American Journal of Managed Care found that insulin glargine-yfgn use among older adults remains low despite cost-effectiveness, and identified several barriers:

1. Prescribing inertia: Clinicians tend to continue prescribing the reference product they know, particularly for chronic conditions like diabetes where switching carries perceived risk
2. Formulary and reimbursement challenges: Even where interchangeable products are preferred on formulary, reimbursement and coverage issues create administrative friction
3. Pharmacy channel limitations: Not all pharmacies stock interchangeable biosimilars, and some may lack awareness of substitution authority
4. Device differences: Patients may be unfamiliar with the injection device used by the biosimilar (e.g., Semglee pen vs. Lantus SoloStar), creating adherence concerns
5. Patient awareness: Many patients are unaware that an interchangeable biosimilar exists and that their pharmacist can substitute it

Manufacturer support programs

Lantus (Sanofi)

• Sanofi Patient Connection: copay assistance, patient assistance program, and bridge supply
• Lantus Savings Card: reduces out-of-pocket costs for eligible commercially insured patients
• Insulins Valyou Savings Program: flat monthly cost option for uninsured patients

Semglee / Insulin Glargine-yfgn (Biocon/Viatris)

• Viatris Patient Assistance Program: benefits verification, copay assistance for commercially insured patients
• Unbranded insulin glargine-yfgn offered at 65% discount to Lantus list price

Rezvoglar (Eli Lilly)

• Lilly Insulin Value Program: cap on out-of-pocket costs
• Lilly Cares: patient assistance for eligible patients
• Rezvoglar copay savings card for commercially insured patients

Langlara (Lannett/Sunshine Lake Pharma)

• Patient support program details are being established following 2026 FDA approval
• Contact Lannett for current access and affordability resources

Basaglar (Eli Lilly)

• Included in Eli Lilly's broader insulin affordability programs
• Basaglar copay savings card available for commercially insured patients

What to monitor

• Langlara market entry: Langlara received FDA approval in 2026 as the third interchangeable insulin glargine biosimilar. Watch for formulary decisions and pricing from the Big Three PBMs in 2026 and 2027.
• Rezvoglar adoption: Despite interchangeable status since 2022, Rezvoglar has captured minimal market share (0.8% of insulin glargine claims as of October 2025). Monitor whether Lilly's distribution strategy and formulary contracting shift this trajectory.
• State substitution law updates: Several states continue to update their biosimilar substitution statutes. Changes in notification requirements or mandatory substitution provisions could accelerate or constrain interchangeable insulin adoption.
• PBM private-label dynamics: The Big Three PBMs have increasingly launched private-label biosimilars. Monitor whether any PBM introduces a private-label interchangeable insulin glargine product, which could reshape formulary dynamics.
• IRA insulin provisions: The $35 monthly insulin cost-sharing cap eliminated a major price differential argument for biosimilars in Medicare. Monitor whether this reduces payer incentive to drive biosimilar adoption.
• Insulin glargine market consolidation: With the CDC reporting 40.1 million Americans living with diabetes and approximately 3.8 million starting insulin within a year of diagnosis, the long-acting insulin market remains large enough to sustain multiple products, but margin pressure from interchangeable biosimilars will continue to intensify.

Sources

• FDA. "FDA Approves First Interchangeable Biosimilar Insulin Product for Treatment of Diabetes." July 28, 2021. Available at: https://www.fda.gov/news-events/press-announcements/fda-approves-first-interchangeable-biosimilar-insulin-product-treatment-diabetes.
• Managed Healthcare Executive. "Langlara, third interchangeable biosimilar to Lantus, approved by FDA." 2026. Available at: https://www.managedhealthcareexecutive.com/view/langlara-third-interchangeable-biosimilar-to-lantus-approved-by-fda.
• American Journal of Managed Care. "Initiation of the Interchangeable Biosimilar Insulin Glargine-yfgn Among Older Adults." April 2026; 32(4): e126-e132.
• Pharmacy Times. "FDA Expands Pharmacist Authority with New Insulin Biosimilar Approval."
• Express Scripts. "2026 National Preferred Formulary Exclusions." Available at: https://www.express-scripts.com/pdf/formulary/NPF_Preferred_Formulary_Exclusions2026.pdf.
• Managed Healthcare Executive. "OptumRx Excludes the Diabetes Biosimilar Semglee from Formulary." 2021.
• GaBI Online. "Interchangeable insulin glargine biosimilar preferred on Express Scripts." July 2025.
• CRS Report R47409. "Insulin Coverage Under Private Health Insurance and Medicare Part D: In Brief." Available at: https://www.congress.gov/crs-product/R47409.
• TechTarget Pharma Life Sciences. "Exploring FDA-approved biosimilar insulin products." 2025.
• Health Affairs. "Improved Insurance Coverage Increased Biosimilar Semglee's Market Share." 2025.
• Drug Channels. "The Big Three PBMs' 2026 Formulary Exclusions." January 22, 2026. Available at: https://www.drugchannels.net/2026/01/the-big-three-pbms-2026-formulary.html.
• CDC. "National Diabetes Statistics Report." March 2026.