In a bid to fight rising specialty drug costs, the largest US health insurer, UnitedHealth, said Monday it would acquire Illinois-based group Catamaran for $12.8 billion (11.8 billion euros).

Catamaran assists employers and health insurers in obtaining prescription drugs at a lower rate from pharmaceutical groups and is known as a pharmacy-benefit company.

Management in that area has become increasingly crucial for controlling costs within the pharmacy market expected to expand from $100 billion in revenue in 2014 to as much as $400 billion annually by 2020.

Good news for shareholders

UnitedHealth said it would pay $61.50 per share for Catamaran and would merge the acquired business with its own unit providing the same service.

The two firms said their deal would combine businesses that have "distinctive, rapidly growing specialty pharmacy services."

The transaction is expected to close during the fourth quarter. Catamaran shares rose by 24 percent an hour before markets opened on Monday, with UnitedHealth shares also up about the same time, albeit only by 3.8 percent.

hg/cjc (Reuters, AP, AFP)