Semglee (insulin glargine-yfgn) is a long-acting basal insulin and the first FDA-approved interchangeable biosimilar to Lantus, designated in July 2021. It is used once daily as basal insulin coverage in adults and pediatric patients with type 1 diabetes (T1D) and adults with type 2 diabetes (T2D). Interchangeability is a meaningful regulatory distinction — it allows pharmacist-level substitution for Lantus without prescriber contact.
What Semglee Is
Semglee (insulin glargine-yfgn injection 100 units/mL) is a long-acting human insulin analog developed by Biocon Biologics and Viatris (formerly Mylan). It is structurally identical to insulin glargine, the active ingredient in Lantus, with the same amino acid sequence and the same modified solubility profile that allows once-daily subcutaneous dosing. Semglee was first approved by the FDA in 2020 as a biosimilar to Lantus and then received the additional interchangeable designation in July 2021, becoming the first interchangeable biosimilar insulin in the US.
Why Interchangeability Matters
Under the Biologics Price Competition and Innovation Act (BPCIA), a biosimilar can earn an additional designation of “interchangeability” by meeting higher evidentiary standards, including switching studies that demonstrate no increased safety or efficacy risk when patients alternate between the reference product and the biosimilar. With this designation, the biosimilar can be substituted for the reference product by a pharmacist without consulting the prescriber, similar to how generic small-molecule drugs are substituted. State pharmacy laws still govern the specific substitution rules. Per the FDA’s announcement, this was a milestone for biosimilar insulin access. Other glargine products like Basaglar are biosimilars but not interchangeable, so a Basaglar prescription must specifically name the product.
Indications
Semglee is FDA-approved to improve glycemic control in:
- Adults with type 2 diabetes
- Adult and pediatric patients (age 6 and older) with type 1 diabetes
It is delivered subcutaneously by 10 mL vial or 3 mL prefilled pen. Common candidates include people with T2D progressing past oral therapy and GLP-1 agonists who need basal coverage, people with T1D needing 24-hour basal coverage between bolus mealtime doses, and patients switching from Lantus or other basal insulins for cost or coverage reasons.
How Semglee Works
Insulin glargine forms a microprecipitate at the subcutaneous injection site at physiologic pH, releasing slowly into the bloodstream over approximately 24 hours. Per the Semglee prescribing information, onset of action is approximately 1 to 4 hours, with no pronounced peak, and a duration of action of approximately 24 hours. This relatively flat profile supports once-daily dosing in most patients, though some T1D patients may need split twice-daily dosing for adequate 24-hour coverage.
| Property | Semglee | Lantus | Basaglar |
|---|---|---|---|
| Active ingredient | Insulin glargine-yfgn | Insulin glargine | Insulin glargine |
| Onset | 1-4 hours | 1-4 hours | 1-4 hours |
| Duration | ~24 hours | ~24 hours | ~24 hours |
| FDA designation | Interchangeable biosimilar | Reference (originator) | Follow-on biologic |
| Pharmacist substitution allowed | Yes (subject to state law) | — | No — must be specifically prescribed |
Dosing
Insulin-naive adults with T2D typically start at 10 units once daily or 0.1 to 0.2 units per kilogram of body weight, titrated by 1 to 2 units every few days based on fasting glucose. Target fasting glucose is generally 80 to 130 mg/dL but should be individualized. For T1D, basal insulin makes up roughly 40 to 50 percent of total daily insulin, with bolus mealtime insulin (Humalog, Novolog, or Fiasp) providing the rest. Switching from Lantus to Semglee is unit-for-unit. Switching from twice-daily NPH to once-daily Semglee usually requires a 20 percent total dose reduction to avoid hypoglycemia.
Side Effects
The most common adverse reactions are hypoglycemia, weight gain, peripheral edema, lipodystrophy with repeated injection in the same area, injection site reactions (redness, itching, swelling), and rare allergic reactions. Hypoglycemia is the dose-limiting toxicity of any insulin. Hypokalemia can occur with insulin therapy. Severe hypersensitivity reactions and worsening of pre-existing heart failure (with concomitant thiazolidinediones) are listed warnings. For people with prediabetes who may eventually need basal insulin, our treatment hub covers earlier-line options and the A1C levels guide covers monitoring goals.
Branded vs Unbranded Semglee
Viatris markets two versions of the same product: branded “Semglee” with full marketing support, and “insulin glargine-yfgn” sold without the brand name at a substantially lower list price. Both contain the identical product. The unbranded launch in late 2021 introduced one of the lowest list prices for any basal insulin in the US, helping pressure overall insulin prices downward. Pharmacists can dispense either version under an interchangeability substitution.
Cost and Coverage
Semglee was developed in part as a cost-reduction strategy in response to long-standing concerns about insulin affordability in the US. Manufacturer savings programs are available for commercially insured patients. Medicare Part D enrollees benefit from the federal $35 monthly insulin cap. Cash price for the unbranded version has been reported at roughly 65 to 70 percent below the original Lantus list price, although actual costs vary by pharmacy and insurance plan.
How Semglee Fits in a Treatment Plan
Per ADA Standards of Care, basal insulin is typically added when A1C remains above target despite oral agents and GLP-1 agonists. Semglee, Lantus, Basaglar, Toujeo (glargine U-300), and Tresiba (degludec) are common starting choices. Semglee’s interchangeability designation makes it especially easy for pharmacies to substitute when a Lantus prescription comes through, often delivering cost savings to the patient automatically.
The Bottom Line
Semglee is the first FDA-designated interchangeable biosimilar insulin in the US, allowing pharmacist substitution for Lantus without prescriber contact. It contains the same insulin glargine molecule, has the same dosing and indications, and shows comparable safety and efficacy. The interchangeability designation matters for access and price — it is the most consequential change in basal insulin pricing in years, and it makes biosimilar uptake far easier than with Basaglar.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting, stopping, or changing any medication or treatment plan.
