Swiss drugmaker Roche Holding said it agreed to acquire US biotech firm InterMune in a multi-billion-dollar deal, as pharmaceutical firms across the globe look to consolidate.

Roche will acquire InterMune for $8.3bn (£5bn, €6.3bn) or $74 per share in an all-cash transaction. The price represents a premium of 38% to InterMune's closing price on 22 August.

"Our offer provides significant value to InterMune's shareholders and this acquisition will complement Roche's strengths in pulmonary therapy," said Severin Schwan, CEO of Roche.

"We look forward to welcoming InterMune employees into the Roche Group and to making a difference for patients with idiopathic pulmonary fibrosis, a devastating disease."

Under the terms of the agreement, Roche will commence a tender offer no later than 29 August, to acquire all outstanding shares of InterMune common stock. The tender offer will be recommended by the board of InterMune.

The transaction is expected to be neutral to core earnings per share in 2015 and accretive from 2016 onwards, Roche said.

InterMune develops innovative therapies in pulmonology and fibrotic diseases. Its lead medicine pirfenidone is approved for the fatal disease idiopathic pulmonary fibrosis (IPF) in the EU and Canada and is under regulatory review in the US.

The acquisition will allow Roche to broaden and strengthen its respiratory portfolio globally. It currently markets Pulmozyme and Xolair in the US and has other novel therapeutic medicines targeting respiratory diseases in clinical development.

"This merger recognizes the significant value created by our team's commitment, hard work and execution for more than a decade to develop and commercialize treatment options for IPF patients and their families," said InterMune's CEO, Dan Welch.

"Roche shares our passion and commitment to the IPF community and to ensuring that pirfenidone is available as quickly as possible to patients in the United States, pending FDA approval."

Roche's global resources and scale will not only facilitate and accelerate our ability to deliver pirfenidone to more patients around the world, but also to realize our joint vision to bring additional innovative therapies to patients with respiratory diseases."

Roche earlier agreed to buy US-based Seragon Pharmaceuticals, which specialises in breast cancer treatments and research, for $725m.

The deal comes as pharmaceutical firms across the globe look to consolidate their operations.

Recent large deals in the sector include AbbVie Inc's $54bn acquisition of Shire Plc and Medtronic Inc's acquisition of Covidien Plc for $43bn.

Meanwhile, Britain's AstraZeneca rejected a $118bn takeover attempt by Pfizer Inc.