FDA Approves Kirsty as First Interchangeable Insulin Aspart Biosimilar

The FDA has announced a significant advancement in diabetes care with the approval of Kirsty (insulin aspart-xjhz), marking it as the first rapid-acting interchangeable biosimilar product to Novolog (insulin aspart).1 This pivotal approval is a crucial step toward enhancing access to more affordable insulin options for the over 8.4 million Americans who depend on insulin therapy to manage their condition.2

The approval also makes Kirsty the second insulin aspart biosimilar to receive FDA clearance. It follows Merilog (insulin-aspart-szjj), approved in February 2025, the first biosimilar to reference Novolog.3 Merilog was the third overall insulin biosimilar approved, after 2 insulin glargine products: Semglee (insulin glargine-yfgn) and Rezvoglar (insulin glargine-aglr).

Upon launch, Kirsty will be available as a 3-mL single-patient-use prefilled pen and a 10-mL multiple-dose vial.1 It is indicated to improve glycemic control in both adult and pediatric patients with diabetes. Similar to Novolog, Kirsty can be administered subcutaneously into the abdomen, buttocks, thighs, or upper arms, typically within 5 to 10 minutes before a meal.

The 10-mL vial can also be used for continuous subcutaneous infusion or intravenously. Dosing must be individualized, and the medication should not be used during hypoglycemia or in patients with hypersensitivity to insulin aspart products. Serious adverse effects include hypoglycemia, severe allergic reactions, and hypokalemia. Common adverse effects may include injection site reactions, rash, lipodystrophy, weight gain, and swelling in the hands and feet.

What’s the Deal With Interchangeability?

The designation of "interchangeable biosimilar" is particularly significant for patient access and market dynamics. The added benefit of an interchangeable biosimilar is that it may be substituted for the reference product (Novolog) at the pharmacy without the need for a new prescription, depending on state laws.3 This capability is expected to streamline patient access and further drive competition.

The high cost of reference insulin products has long been a critical issue in the US, which has over 37 million people diagnosed with diabetes.2 This financial burden often forces patients to skip or ration their insulin treatments to save money. A JAMA study highlighted this challenge, finding that 1 in 5 US adults under 65 years with diabetes who use insulin rationed their supply due to cost.4 Notably, nearly 71% of adults reporting insulin rationing for financial reasons were under 65 years, making them ineligible for the out-of-pocket cost limits established by the Inflation Reduction Act.

The FDA's ongoing approval of additional insulin biosimilars, especially interchangeable ones, underscores its commitment to fostering a competitive marketplace for insulin products.1

Increasing access to safe, effective, and high-quality medications at potentially lower price points remains an ongoing priority for the FDA. In a statement touting the approval of Miralog, Sarah Yim, MD, director of the Office of Therapeutic Biologics and Biosimilars, further emphasized that "having a biosimilar option for their rapid-acting insulin injection can truly make a difference, as biosimilar products have the potential to increase access to these life-saving medications."3

The availability of biosimilar and interchangeable insulin products is expected to provide more treatment options, potentially lowering costs, and ultimately enabling greater access for more patients.

References

1. FDA approves first interchangeable biosimilar insulin product to Novolog (insulin aspart). News release. FDA. July 15, 2025. Accessed July 15, 2025. https://content.govdelivery.com/accounts/USFDA/bulletins/3e995f3

2. American Diabetes Association announces support for INSULIN Act at Senate press conference. News release. ADA. June 22, 2022. Accessed July 15, 2025. https://diabetes.org/newsroom/american-diabetes-association-announces-support-for-insulin-act-at-senate-press-conference

3. Jeremias S. FDA approves first insulin aspart biosimilar. The Center for Biosimilars®. February 17, 2025. Accessed July 15, 2025. https://www.centerforbiosimilars.com/view/fda-approves-first-insulin-aspart-biosimilar

4. Fang M, Selvin E. Cost-related insulin rationing in US adults younger than 65 years with diabetes. JAMA. 2023;329(19):1700-1702. doi:10.1001/jama.2023.5747