* Firazyr to be reviewed by US advisory panel Thursday
* Sales seen topping $100 mln by 2015
* Shire shares rise 0.6 percent (Adds analyst comment, sales details)
NEW YORK, June 21 (Reuters) - Shire Plc's (SHP.L) drug to treat severe swelling caused by a rare genetic disorder showed effectiveness in a key clinical trial, U.S. Food and Drug Administration staff said on Tuesday.
The injected drug, Firazyr, is under U.S. review for treating attacks suffered by patients with hereditary angioedema.
FDA staff issued a report on the drug, which is approved in other countries, ahead of a federal advisory committee meeting to review the medicine on Thursday.
The clinical trial, known as FAST-3, was conducted to address the FDA's concerns over the drug's efficacy from two earlier studies. The agency declined to approve the drug in April 2008, citing clinical deficiencies.
In FAST-3, Firazyr, or icatibant, showed a statistically significant decrease in time to primary symptom relief, FDA staff said.
"Collectively, the findings from the Phase 3 clinical program support the efficacy of icatibant for the proposed indication," FDA staff said in their documents.
The agency also found no pattern of serious adverse events across the studies that appeared attributable to Firazyr.
The FDA is expected to make a decision on Firazyr by Aug. 25.
Shares of Shire were up 0.6 percent in London.
Hereditary angioedema is a rare and dangerous genetic disease characterized by sudden attacks of swelling in areas such as hands, arms, feet, face or breathing passages. It is estimated to affect one in 50,000 people.
Firazyr is already approved in more than 35 countries in Europe and elsewhere. Analysts on average expect the drug's sales to reach $107 million by 2015, according to Thomson Reuters Pharma, after Shire reported $11 million in Firazyr sales last year. The company reported overall revenue of nearly $3.5 billion in 2010.
Deutsche Bank analyst Mark Clark said he was confident the drug would win approval following the FDA staff release of the documents. Shire initially put Firazyr's sales potential at as much as $450 million, but the U.S. delay and arrival of competitors has dampened expectations, Clark said in a research note.
U.S. sales of Viropharma Inc's VPHM.O Cinryze, a rival drug approved in October 2008, reached $177 million last year, Clark said.
Shire has a significant business in drugs for rare genetic disorders, such as Gaucher disease and Fabry disease. (Reporting by Lewis Krauskopf; Editing by Lisa Von Ahn)