Otsuka Pharmaceutical Co., Ltd (Otsuka) announces that the European Commission (EC) has granted marketing authorization for Dawnzera™ (donidalorsen) for the routine prevention of recurrent attacks of hereditary angioedema (HAE) in adults and adolescents aged 12 years and older.

HAE is a genetic condition which causes unpredictable swelling episodes that can affect the extremities, face, abdomen, genitals and the larynx.¹ Approximately 50% of people with HAE experience their first symptoms by the age of 10 with the majority experiencing symptoms or their first attack by 18 years of age.² Anxiety and depression are common in patients with HAE, often stemming from the unpredictable nature, frequency, and severity of swelling episodes.^3,4,5

The pivotal, double-blind, placebo-controlled, Phase 3 OASIS-HAE study (n=90) showed the use of donidalorsen 80mg every four weeks (Q4W) led to an 81% reduction in 4-weekly HAE attack rate compared to placebo (mean attack rates 0.44 vs. 2.26 respectively) over 24 weeks, meeting the study's primary endpoint. A 55% reduction (mean attack rate 1.02) compared to placebo was observed with dosing every eight weeks (Q8W).⁶

At week 24, 91% of donidalorsen Q4W patients had well-controlled disease compared to 41% of patients in the placebo group, as measured by the Angioedema Control Test, and improvements in quality of life were observed, demonstrated by a reduction from baseline of 24.8 points in mean Angioedema Quality-of-Life total score. ⁶

No major safety concerns were identified in the study, with similar Q4W and Q8W dosing adverse event profiles. ⁶ The most common adverse events with donidalorsen include injection site reactions, increased hepatic enzymes and hypersensitivity (including anaphylaxis).⁷

Ionis Pharmaceuticals, Inc. and Otsuka Pharmaceutical Co., Ltd entered the initial license agreement for the commercialization of donidalorsen in Europe in 2023, with the agreement later broadening to Asia Pacific. Ionis has maintained the clinical development of donidalorsen as well as the responsibility for its launch in the United States with Otsuka utilizing its expertise in rare disease and commercial infrastructure to prepare for future market launches.

"We are proud of the decision from the European Commission to authorize the use of donidalorsen in HAE. This represents another key milestone in the collaboration between Otsuka and Ionis which aims to address unmet need in a challenging rare disease," said Andy Hodge, President and CEO at Otsuka Pharmaceutical Europe Ltd. "We would like to thank all those at Otsuka and Ionis whose commitment has helped us introduce this medicine to HAE patients."

The decision follows the positive opinion issued by the Committee for Medicinal Products for Human Use (CHMP) in November 2025. The new authorization applies to all 27 EU member states, as well as Iceland, Liechtenstein, and Norway.

About Dawnzera™ (donidalorsen)

Donidalorsen is a first-in-class, RNA-targeted prophylactic therapy which is administered subcutaneously.⁶ It is a ligand-conjugated antisense oligonucleotide (ASO) that reduces prekallikrein production in the liver, interrupting the pathway that leads to HAE attacks.^6,8

In August 2025, the U.S. Food and Drug Administration (FDA) approved donidalorsen for prophylaxis to prevent attacks of HAE in adults and children aged 12 years and older.⁹

About hereditary angioedema (HAE)

Hereditary angioedema (HAE) is a rare, chronic, and potentially life-threatening genetic condition affecting approximately 15,000 people in Europe.¹⁰ HAE, most commonly caused by the inherited deficiency or dysfunction of C1 esterase inhibitor (C1-INH), results from uncontrolled activation of the plasma kallikrein-kinin system, leading to excessive bradykinin production.^11,12,13 Symptoms of HAE usually begin in childhood or early adulthood, with some individuals experiencing their first episodes as young as 2 years old.^4,11

About Otsuka

Otsuka Pharmaceutical Co., Ltd. is a total healthcare company that focuses on each individual's potential to enhance their well-being. Our medical-related business provides treatments and diagnostics for both physical and mental health. Our nutraceutical business supports daily health maintenance and improvement. Otsuka's unique products and services are based on scientific evidence, under the guidance of our corporate philosophy: Otsuka-people creating new products for better health worldwide. For further information, please visit www.otsuka.co.jp/en/

1. 1.Raasch J, et al. World Allergy Organ J 2023;16(6):100792.
2. 2.HAE International. Attack Triggers. Available at: https://haei.org/what-is-hae/attack-triggers/ Accessed December 2025
3. 3.Chong-Neto HJ, World Allergy Organ J 2023;16(3):100758
4. 4.Busse P, et al. J Allergy Clin Immunol Pract 2021;9(1):132-150.e3
5. 5.Banerji A, et al. Ann Allergy Asthma Immunol 2020;124:600-607.
6. 6.Riedl MA, et al. N Engl J Med 2024;391(1):21-31.
7. 7.European Medicines Agency. Dawnzera. Available at: https://www.ema.europa.eu/en/medicines/human/EPAR/dawnzera Accessed December 2025 Accessed December 2025
8. 8.Riedl MA, et al. J Allergy Clin Immunol Pract 2025;13(9):2381-2389.
9. 9.U.S. Food and Drug Administration. Orphan Drug Designations and Approvals - Donidalorsen. Available at: https://www.accessdata.fda.gov/scripts/opdlisting/oopd/detailedIndex.cfm?cfgridkey=961723 Accessed December 2025
10. 10.Lumry WR. Hereditary angioedema: the economics of treatment of an orphan disease. Front Med (Lausanne). 2018;5:22.
11. 11.Maurer M, et al. Allergy 2022;77(7):1961-1990.
12. 12.Santacroce R, et al. Review J Clin Med 2021:10(9):2023.
13. 13.Longhurst HJ, Bork K. Br J Hosp Med (Lond) 2019:2;80(7):391-398.