Elan, the Irish drug maker facing a hostile takeover bid from Royalty Pharma, has announced that it is putting itself up for sale.

The company has urged its shareholders not to tender into the current $7.8bn Royalty Pharma offer, but said the US private equity firm will be invited to participate in the latest sale process "if they so wish".

"Elan Corporation today announced that it is proceeding with a formal sale process in light of the expressions of interest received to date," the company said in a statement on Friday.

The sale suggests that the two firms may finally end a feud that has lasted almost four months, but in an open letter to Elan, Royalty Pharma co-founder and chairman Rory Riggs called the move a "fruitless effort to find a buyer willing to offer more than we are."

"We believe that our offer is the best alternative for Elan’s shareholders now and will remain the best alternative upon completion of Elan’s sale process."

"The company has urged its shareholders not to tender into the current $7.8bn Royalty Pharma offer."

The sale sindicates that Elan may be giving up on its plans to remain as an independent healthcare company, after it agreed to buy two private drug companies and outlined plans to buy back more shares in May.

Elan said it will buy AOP Orphan, an Austrian company focused on rare and orphan diseases, for €263.5m, and pay $40m for a 48% stake in Dubai-based sales and marketing firm Newbridge Pharmaceuticals.

Elan’s financial advisors are Citigroup, Davy Corporate Finance, Morgan Stanley and Ondra Partners. Its legal advisors are A&L Goodbody and Cadwalader, Wickersham & Taft.