LONDON -(Dow Jones)- Shire PLC (SHP.LN) Thursday said U.S. drug regulators have approved its new drug Firazyr for the treatment of a rare swelling disorder.

The product will be the first on-demand treatment for hereditary agiodema, or HAE, that adult patients can use to inject themselves when they feel an attack coming on, instead of seeking a health-care professional.

Firazyr is an orphan drug, meaning it has been developed specifically for the treatment of a rare disease and gets patent exclusivity for longer than usual.

HAE is a potentially fatal condition that causes severe swelling in the hands and feet, gastrointestinal tract and upper airway and is believed to affect 6, 000 to 30,000 people in the U.S.

"Firazyr is a treatment with demonstrated efficacy that can be carried and stored at room temperature and self-injected by the patient," said Timothy Craig, professor of medicine and pediatrics at Penn State Hershey Medical Center. "Firazyr addresses this important unmet need by providing HAE patients with fast access to acute treatment."

Sylvie Gregoire, president of Shire HGT, said, "With Firazyr now approved in 38 countries, we are pleased to bring both this novel treatment and our comprehensive OnePath patient service and support program to U.S. HAE patients."

Firazyr's approval by the Food and Drug Administration was widely expected after an FDA advisory panel backed it in June.

Shire shares fell earlier Thursday after the U.K. specialty drug maker's bio- engineered skin substitute Dermagraft failed in a late-stage clinical trial for treating venous leg ulcers, prompting analysts to trim their sales forecasts for the product.

The stock ended the day's trading in London down 2.8% at 1,955 pence, but up 38% on year.