UK drugmaker Shire is hailing “an excellent first quarter performance” after revenues for the first quarter of 2010 remained flat despite generic competition to Adderall XR.

The group said sales of its core products actually jumped 36% to $626 million, with the new attention-deficit hyperactivity disorder drug Vyvanse (lisdexamfetamine dimesylate) up 32% to $154 million, Elaprase (idursulfase) for Hunter syndrome up 22% to $101 million, and Replagal (agalsidase alfa), for the treatment of Fabry disease, up 69% to $68 million, all leading the way.

However, turnover of the company’s veteran ADHD drug Adderall XR (amphetamine salts), which has had to grapple with copycat competition since the year-ago quarter, dragged on results after plummeting 69% to $92 million.

And, while sales stayed flat, higher costs recorded in the research and development and selling, general and administrative columns drove non-GAAP operating income down 19% to $265 million.

Still, the company ended the period with more cash in its pocket - $684 million versus $532 million a year ago – and remains confident about its performance in the remaining quarters of the year.

“With the expected growth in 2010 we reiterate our aspirational target of mid-teens revenue growth on average between 2009 and 2015,” said Angus Russell, Shire’s chief executive.