Shire, the London-listed drugmaker targeted by Takeda Pharmaceutical, today reported a 6% rise in first-quarter earnings.

But the company kept its cautious outlook for the year in the face of increasing drug competition. 

Shire is willing to recommend a $64 billion offer from Takeda to shareholders, in what would be the biggest acquisition of a drug company since 2000, but investors see risks to the ambitious deal being consummated.  

Currency factors flattered Shire sales in the quarter as it felt the impact of falling sales of its flagship ulcerative colitis drug Lialda. Early generic competition to Lialda has added to Shire's recent problems. 

Earnings in the quarter were helped by higher sales of drugs for rare diseases and a lower tax rate, partially offset by lower gross margins. 

Quarterly revenue of $3.77 billion was slightly ahead of analysts' forecasts of $3.72 billion. 

In the 30 years since it started out as small business selling calcium supplements from above a shop in southern England in 1986, Shire became a poster child for a nimble specialty drugs firm, driven by smart dealmaking. 

But the stock lost its lustre two years ago after its biggest ever deal, the $32 billion acquisition of Baxalta, which increased its exposure to the haemophilia treatment market at a time of major uncertainty.