FDA-Designated Denosumab Biosimilars Enter US Market

Biocon Limited has begun commercial distribution of two denosumab biosimilars in the United States.1 The launch features Bosaya (denosumab-kyqq), a biosimilar to Prolia, which is available as a 60 mg/mL injection for subcutaneous use in a prefilled syringe. Additionally, Aukelso (denosumab-kyqq), a biosimilar to Xgeva, which is available as a 120 mg/1.7 mL injection for subcutaneous use in a single-dose vial. These new products entering the market mark another step in the continued expansion of the country's biosimilar market into high-value reference products.

Both products received approval and interchangeable designation from the FDA in September 2025 and are now available nationwide through specialty pharmacies and healthcare providers.1 The interchangeable designation demonstrates not just biosimilarity, but that patients can switch between the biosimilar and the reference product without increased safety or efficacy risk compared to remaining on the reference alone.

What Does the Market Opportunity Look Like?

An estimated 10 million adults over 50 years of age have osteoporosis in the US, with another 44 million at risk due to low bone density.1 One in two women and up to one in four men over age 50 will fracture a bone in their lifetime because of this disease. Both products also carry indications relevant to giant cell tumor of bone, a rare, locally aggressive benign tumor that causes significant pain and disability in young adults. In 2024 alone, Denosumab products generated approximately $5 billion with US sales.

Denosumab functions as a human monoclonal antibody targeting receptor activator of nuclear factor kappa-B ligand, which is essential for the formation, function, and survival of osteoclasts — the cells responsible for bone resorption.1 By blocking this pathway, the molecule reduces bone breakdown and increases bone mass and strength.

"The U.S. introduction of Bosaya and Aukelso marks a strategic expansion of our biosimilars portfolio, building on our established leadership in oncology and immunology,” Shreehas Tambe, chief executive officer and managing director, Biocon Limited, said in a press release.1 “These therapies broaden access to high-quality, affordable treatment options for patients living with serious bone conditions. This milestone underscores Biocon's strength as a portfolio development engine and our focus on building the world's most scalable access platform — advancing life-changing medicines for patients and health systems across the United States and around the world."

What Are the Key Safety and Manufacturing Considerations?

Bosaya carries a boxed warning related to severe hypocalcemia in patients with advanced chronic kidney disease, including those on dialysis, which fatal cases have been reported.1 Pre-existing hypocalcemia must be corrected before initiation, and all patients require adequate calcium and vitamin D supplementation. Additional warnings cover hypersensitivity reactions including anaphylaxis, osteonecrosis of the jaw, atypical femoral fractures, multiple vertebral fractures following treatment discontinuation, serious infections, dermatologic reactions, and significant suppression of bone turnover. In postmenopausal osteoporosis trials, the most commonly reported adverse reactions exceeding 5% and more frequent than placebo included back pain, pain in extremity, high cholesterol, musculoskeletal pain, and cystitis.

Aukelso carries overlapping warnings such as hypocalcemia, osteonecrosis of the jaw, atypical femoral fractures, hypersensitivity, and multiple vertebral fractures following discontinuation.1 Additionally, warnings around hypercalcemia following treatment discontinuation in patients with giant cell tumor of bone and in those with growing skeletons were also included. Patients with a creatinine clearance below 30 mL/min or on dialysis carry elevated hypocalcemia risk and require supplementation. In bone metastasis trials, the most common adverse reactions occurring in at least 25% of patients were fatigue, low phosphate levels, and nausea.

How Is the Biosimilar Landscape Shifting?

The Biocon launches were likely facilitated by alterations to regulatory standards at the federal level as the FDA published draft guidance proposing to reduce the requirement for comparative efficacy studies.2 This step currently takes one to three years and costs an average of $24 million, allowing developers to rely more heavily on analytical testing to demonstrate biosimilarity. The agency also announced it no longer generally recommends switching studies for interchangeable designation, a requirement that has historically added development time and cost.

References

1. Biocon announces U.S. commercial launch of Bosaya and Aukelso, denosumab biosimilars. Biocon Ltd. Published April 7, 2026. Accessed April 7, 2026. https://www.biocon.com/biocon-announces-u-s-commercial-launch-of-bosaya-and-aukelso-denosumab-biosimilars/
2. FDA accelerates biosimilar development and lowers drug costs. U.S. Food and Drug Administration. HHS.gov. Published October 28, 2025. Accessed April 7, 2026. https://www.hhs.gov/press-room/fda-accelerates-biosimilar-development-and-lowers-drug-costs.html