Strong demand for Shire's top-selling Vyvanse drug helped to lift first-quarter earnings by a better than expected 12%.
The news boosted the company's shares ahead of its $32 billion acquisition of US rare diseases specialist Baxalta.
Sales of Vyvanse, a treatment for attention deficit hyperactivity disorder (ADHD), rose 22%, partly reflecting the drug's recent approval as a treatment for binge eating disorder (BED).
"Shire is off to a strong start in 2016," the company's chief executive Flemming Ornskov, who has faced investor criticisms over his pay, said.
Shire said its combination with Baxalta was on track, with shareholder votes set for May 27 and the deal expected to close in early June.
Baxalta, which makes drugs for rare blood conditions, cancers and immune system disorders, is Shire's biggest acquisition to date and will make it a global leader in rare diseases, with annual sales of over $20 billion by 2020.
Ornskov said that planning for the integration of Baxalta was proceeding more rapidly than initially expected but declined to say if this would enable Shire to exceed forecast cost savings of $500m a year by the third year of the merger. Many analysts view that figure as conservative.
Forecasts would be revised after the Baxalta deal is formally concluded, Ornskov said.
The company reporteds first-quarter earnings per share of $3.19 on revenue up 17% to $1.71 billion. This compared with analysts' consensus forecasts of $3.05 billion and $1.69 billion respectively.
Shire faced a protest over executive pay at its annual meeting earlier this week, with a 49% vote against the company's director remuneration report, which included a 25% pay increase granted to Ornskov last year.
