Basaglar and Lantus both contain insulin glargine at the same concentration (100 units/mL), and they have the exact same amino acid sequence. They are not, however, identical products. Basaglar is manufactured by Eli Lilly using a different production process than Sanofi’s Lantus, and the FDA classifies it as a “follow-on biologic” rather than a generic or a true biosimilar. In practice, the two work the same way in your body, but they aren’t automatically interchangeable at the pharmacy.
Same Molecule, Different Classification
Insulin glargine is a long-acting insulin analog that keeps blood sugar steady over roughly 24 hours. Both Basaglar and Lantus deliver it at U-100 concentration, with the same onset (3 to 4 hours), no pronounced peak, and duration of up to 24 hours. The amino acid sequence is identical.
The distinction is regulatory. Lantus was originally approved through the FDA’s drug pathway, not the newer biologics pathway. That means no company could submit a true “biosimilar” application referencing it. Instead, Eli Lilly and Boehringer Ingelheim brought Basaglar to market in December 2015 as a follow-on biologic, essentially a new drug application that demonstrated comparable safety and efficacy against Lantus. This matters because a follow-on biologic cannot be substituted at the pharmacy counter the way a generic pill can. Your prescriber has to write a prescription specifically for Basaglar if that’s what you or your insurer prefer.
A separate product, Semglee (insulin glargine-yfgn), later earned the FDA’s “interchangeable” designation with Lantus, meaning pharmacists can substitute it without a new prescription. Basaglar does not have that designation.
How Clinical Trials Compared Them
The FDA reviewed two large head-to-head trials before approving Basaglar. In people with type 1 diabetes, Basaglar lowered HbA1c by 0.35 percentage points over 24 weeks, while Lantus lowered it by 0.46 points. The difference of 0.11 points was not statistically significant. In people with type 2 diabetes, both products reduced HbA1c by roughly 1.3 percentage points from identical baselines, with a negligible 0.05-point gap between them.
Safety profiles were also comparable. Rates of severe hypoglycemia showed no difference in either trial. Serious adverse events occurred in 5.4% of people on Basaglar versus 6.5% on Lantus. Allergic reactions were nearly equal (41 cases with Basaglar, 38 with Lantus). The only slight divergence was injection-site reactions: 1.7% with Basaglar compared to 0.9% with Lantus. Antibody development, a concern with any biologic insulin, showed no meaningful difference between the two.
The Pen and Vial Differences
If you’re switching between these two products, the delivery device is the most noticeable change. Lantus comes as both a prefilled SoloStar pen and a multi-dose vial you draw from with a syringe. Basaglar is only available as a prefilled pen, either the KwikPen or the Tempo Pen. There is no Basaglar vial. For anyone who relies on syringes and vials, perhaps for flexibility in dosing or because of an insulin pump setup, this is a real limitation.
Both pens hold 3 mL of insulin (300 units total) and should be stored at room temperature once in use, then discarded after 28 days regardless of how much insulin remains. Unopened pens and vials stay refrigerated until their expiration date.
Cost and Insurance Coverage
Basaglar launched in December 2016 at a list price roughly 15% lower than Lantus. In theory, that should translate to savings. In practice, what you actually pay depends almost entirely on your insurance formulary. Many commercial plans and Medicare Part D plans now favor one product over the other based on rebate agreements negotiated behind the scenes. Some plans cover Basaglar at a lower copay tier, while others prefer Lantus or Semglee.
Research from the Center for Biosimilars found that Basaglar’s lower list price did not consistently translate into lower out-of-pocket costs for patients. The takeaway: check your plan’s formulary or ask your pharmacist which insulin glargine product sits on the preferred tier before assuming one will cost less than the other.
Switching Between the Two
Because Basaglar and Lantus contain the same molecule at the same concentration, switching is typically done at a one-to-one unit dose. You don’t need a conversion calculation the way you would when moving between different types of long-acting insulin. Still, any insulin switch warrants closer blood sugar monitoring for the first few days, since small differences in manufacturing can occasionally affect how your body absorbs a dose.
If your doctor currently prescribes Lantus and your insurer prefers Basaglar (or vice versa), the switch requires a new prescription. Your pharmacist cannot make the swap on their own, unlike with interchangeable biologics such as Semglee. This is one of the practical consequences of Basaglar’s follow-on biologic status. It adds a step, but the clinical transition itself is straightforward for most people.