The US Food and Drug Administration's decision to approve a rival company's petition to market a cheaper version of hyperactivity drug Adderall XR has proved to be costly for British drug maker Shire as its shares slumped by more than 11 percent on Monday
Shire shares plunged 11.70 percent to stand at 1,736 pence -- heading the losers board on London's benchmark FTSE 100 index, which was down 0.96 percent at 5,460.59 points in afternoon trading.
The stock sank after US regulators ruled against Shire, which said in a statement that they had approved generic copies of Adderall XR from Watson Pharmaceuticals' recently acquired Actavis unit.
"Shire announces that the US Food and Drug Administration has responded to its citizen petition for Adderall XR and has approved one abbreviated new drug application for generic Adderall XR," Shire said in a statement.
-- Dow Jones Newswires contributed to this story --