By: Rebecca Sabzanov, PharmD Candidate c/o 2026

On July 15^th, 2025, the FDA approved Kirsty, or insulin aspart-xjhz, as the first interchangeable biosimilar to insulin aspart. ^{1, 2} A biosimilar is a biologic that is very similar to the approved reference product and has no meaningful differences in safety, purity and potency. All insulin products were reclassified from drugs to biologics in 2020 because of the complexity of the products, specifically because insulin is a large-molecule, protein-based medication, and unlike most small-molecule drugs, biologics are more complex and cannot be replicated exactly, therefore it cannot have generic products, only biosimilars.

An interchangeable biosimilar must demonstrate that switching between it and the reference biologic does not lead to decreased efficacy or any increased safety concerns. An interchangeable biosimilar allows pharmacists to substitute the product without contacting the prescriber, where permitted by state law.

The approval was based on results from a 24-week open-label phase 3 trial, which included 478 participants that received insulin glargine once daily along with either insulin aspart-xjhz or the reference product, insulin aspart, at mealtimes. The primary endpoint was the treatment-emergent antibody response (TEAR) rate, which was defined as patients who were anti-insulin antibody negative at baseline and became positive post-baseline, or patients who were AIA positive at baseline and demonstrated a 4-fold increase in titer values post-baseline. Secondary endpoints compared efficacy and included changes from baseline to week 24 in HbA1c values, fasting plasma glucose, prandial, basal and total daily insulin per unit body weight and 7-point self-monitored blood glucose (SMBG) profiles. Additionally, immunogenicity and adverse effects were compared. The results showed that the mean changes from baseline of HbA1c, fasting plasma glucose and insulin dosages were similar in both treatment groups at week 24. Safety profiles, like hypoglycemia, immune-related events and other adverse effects were similar between treatment groups at 24 weeks as well.³ Because of the demonstrated similar immunogenicity, efficacy and safety profiles, the FDA approved insulin aspart-xjhz as an interchangeable biosimilar to insulin aspart.

            Biosimilars to insulin are crucial because they expand access to life-sustaining therapy by having reduced costs. Insulin prices can be a significant barrier for many patients, which can lead patients to skip doses or “ration” their insulin, which can cause many serious complications.^{4, 5} By approving the first biosimilar to insulin aspart, the FDA has helped ensure more patients can access medications they need. Kirsty is available as a 3 mL single-patient-use prefilled pen or a 10 mL multiple-dose vial. It is administered subcutaneously before meals like insulin aspart. Dosing must be individualized based on the patient’s blood glucose levels and other needs and may need to be modified for altered renal or hepatic function.  

REFERENCES

1. FDA Approves First Interchangeable Biosimilar Insulin Product to Novolog (insulin aspart). U.S. Food and Drug Administration. Published 2025. Accessed August 20, 2025. https://content.govdelivery.com/accounts/USFDA/bulletins/3e995f3
2. Jeremias S. FDA Approves Kirsty as First Interchangeable Insulin Aspart Biosimilar. Center for Biosimilars. Published July 15, 2025. https://www.centerforbiosimilars.com/view/fda-approves-kirsty-as-first-interchangeable-insulin-aspart-biosimilar
3. Blevins TC, Raiter Y, Sun B, et al. Immunogenicity, Efficacy, and Safety of Biosimilar Insulin Aspart (MYL-1601D) Compared with Originator Insulin Aspart (Novolog®) in Patients with Type 1 Diabetes After 24 Weeks: A Randomized Open-Label Study. BioDrugs. 2022;36(6):761-772. doi:https://doi.org/10.1007/s40259-022-00554-6
4.  Fang M, Selvin E. Cost-Related insulin rationing in US adults younger than 65 years with diabetes. JAMA. 2023;329(19). doi:https://doi.org/10.1001/jama.2023.5747
5. American Diabetes Association. American Diabetes Association Announces Support for INSULIN Act at Senate Press Conference | ADA. diabetes.org. Published June 22, 2022. https://diabetes.org/newsroom/american-diabetes-association-announces-support-for-insulin-act-at-senate-press-conference