(Reuters) – The U.S. Food and Drug Administration said it approved expanded use of Regeneron Pharmaceuticals Inc and Sanofi SA’s eczema drug Dupixent to include patients aged between 12 and 17, a boost for both the companies in the world’s largest market for drugs.

Shares of Regeneron closed up 2.3 percent at $412.05 on Monday.

The FDA first approved the drug in 2017 and it has since been launched as a treatment for adults with moderate-to-severe atopic dermatitis, or eczema, as well as a drug for some asthma patients.

The companies estimate that there are about 300,000-400,000 adults in the United States who are most in need of treatment, and that the number of adolescent patients is about half of this population.

The new approval allows Dupixent to be prescribed to adolescent patients whose atopic dermatitis cannot be adequately managed with topical prescription medicines, or when such therapies are not advisable, Regeneron said in a statement.

The biologic therapy, delivered as a shot, targets two key proteins that may play a central role in the inflammation underlying certain allergic diseases.

The drug represents an important growth driver for both the companies which are testing its use in patients with conditions like eosinophilic esophagitis as well as food and environmental allergies.

In recent years, Regeneron’s investors have been focusing on newer drugs such as Dupixent, as the company’s flagship drug, Eylea, faces increased competition.

Sanofi has been placing hopes on continued upswing for the drug as it faces weakness in its diabetes business due to generic rivals.

The drug, which brought in $922 million in revenue for Sanofi in 2018, gained a U.S. FDA nod last year for use as a maintenance therapy in patients with two forms of asthma.

Piper Jaffray analysts, before the approval, said they expected U.S. sales of $661 million in 2021 from Dupixent’s use in treating adolescents alone.

(Reporting by Manas Mishra and Tamara Mathias in Bengaluru; Editing by Maju Samuel)

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