GlaxoSmithKline has boosted its pipeline of drugs with a £1.9 billion deal for its American partner on a potential blockbuster medicine.
The proposed acquisition of Human Genome Sciences (HGS) means it has secured the full rights for Benlysta, the first new drug to be approved to treat immune system disease lupus in the US for more than 50 years.
It finally gained boardroom support after HGS directors dismissed a previous offer as inadequate and launched an unsuccessful hunt for an alternative buyer.
Buying the biotechnology company will help GSK further bolster its pipeline of new drugs at a time when the pharmaceutical industry is facing large numbers of patent expiries, leaving products open to being copied by rivals.
GSK offered 14.25 US dollars (£9.15) per share offer - nearly double the price the shares were trading at before the three-month takeover pursuit - valuing HGS at 3 billion US dollars (£1.9 billion). It hopes to find at least 200 million US dollars (£128.4 million) in synergies by 2015.
HGS said Benlysta has shown steady growth in sales since its launch last year but it is thought to have strong opportunities for expansion both in the US, where there are 325,000 lupus patients, and overseas.
Glaxo currently has a profit-sharing agreement with HGS for the drug but the deal will secure all of its revenues. It will also see GSK gain full ownership for type-two diabetes treatment, albiglutide, and darapladib, a possible treatment for atherosclerosis - a hardening of the arteries.
GSK chief executive Sir Andrew Witty said: "We are pleased to have reached a mutually beneficial agreement with HGS on friendly terms and believe the combination of GSK and HGS represents clear financial and strategic logic for both companies and our respective shareholders."
Glaxo has had a near-20 year relationship with HGS, after paying 125 million US dollars (£102 million) in 1993 to establish a research partnership with the company, which has developed a map of all the genes in the human body.
Fears of a so-called patent cliff has been driving consolidation in the pharmaceuticals industry in recent months as giant players look to secure their future pipelines. AstraZeneca last month teamed up with its US partner Bristol-Myers Squibb to buy diabetes drug developer Amylin in a 7 billion dollar (£5.7 billion) deal.