Feb 24 (Reuters) - Dublin-based drugmaker Shire said on Tuesday it had bought U.S. firm Meritage Pharmafor at least $70 million, boosting its gastrointestinal drugsbusiness.

Shire said it had obtained rights to buy privately-heldMeritage in connection with its $4.2 billion acquisition of raredisease specialist Viropharma in 2014. The fee could rise ifdevelopment and regulatory milestones are reached, it said.

The deal comes after Valeant Pharmaceuticals International sealed a $10.1 billion acquisition of gastrointestinaldrugmaker Salix Pharmaceuticals on Sunday, and saidthis week it planned to strike further smaller deals.

Shire had taken initial steps to acquire Salix and wasworking with advisers on a potential offer, according to peoplefamiliar with the matter.

Shares in Shire were down 0.4 percent at 5170 pence at 1232GMT. (Reporting by Neil Maidment; Editing by Greg Mahlich)