A U.S. Food and Drug Administration (FDA) logo, a syringe and a vial are seen in this illustration taken May 13, 2025. REUTERS/Dado Ruvic/Illustration

By Sneha S K and Bageshri Banerjee

(Reuters) -The U.S. Food and Drug Administration on Thursday approved Ionis Pharmaceuticals' drug to prevent instances of severe swelling in various parts of the body of patients with a rare genetic disorder.

Shares of the company were up 1.1% in afternoon trading.

The drug, Dawnzera, is approved as a so-called "prophylaxis" to prevent symptoms of a rare genetic disease called hereditary angioedema (HAE) in adults and pediatric patients 12 years of age and older.

The condition causes frequent attacks of severe swelling in various parts of the body, including the hands, feet, genitals and face.

Dawnzera will be available in the United States in the coming days with a list price of $57,462 per dose, the company said.

HAE is estimated to affect about 7,000 patients in the U.S., according to Ionis.

The drug, chemically known as donidalorsen, prevents HAE attacks by lowering levels of a protein called prekallikrein (PKK) that drives swelling and inflammation.

Dawnzera can be self-administered through an under-the-skin injection once every four or eight weeks.

The approval was supported by late-stage study results that showed the drug, dosed once every four weeks, reduced monthly attacks by 81% compared to a placebo over 24 weeks.

Current FDA-approved therapies for HAE fall into two groups: prophylaxis to prevent attacks and on-demand medicines to treat acute attacks.

Other approved prophylactic drugs include Takhzyro, developed by Japan's Takeda Pharmaceutical and Haegarda from CSL Behring.

There is a lot of excitement for donidalorsen as patients who are not doing well on existing therapies have an option to switch to Dawnzera, which has a higher efficacy, TD Cowen analyst Yaron Werber said ahead of the approval.

Takhzyro, given every two weeks, showed an average of 87% fewer attacks compared to a placebo over 6.5 months in a separate study involving adult and adolescent patients.

Werber estimates peak annual sales of Ionis' drug to be $509 million by 2032.

(Reporting by Bageshri Banerjee and Sneha S K in Bengaluru; Editing by Tasim Zahid and Leroy Leo)