GlaxoSmithKline (GSK), Europe’s largest drugs group, will pay $1.65 billion (£800 million) for an American pharmaceutical company to obtain a market-leading heart disease drug.

GSK will acquire Reliant Pharmaceuticals in an all-cash deal to boost its flagging American performance. The move will bring Lovaza, Reliant’s lead drug, into GSK’s US portfolio.

Lovaza is a nonstatin treatment for high triglycerides, a type of fat found in the blood, which increases the risk of heart disease. Reliant was able to command a high price because the Omega3 drug is capturing an increasing share of a growing market.

It is the only prescription drug of its kind approved by the American Food and Drug Administration and is under patent protection until 2018.

Chris Viehbacher, president of GSK’s American pharmaceuticals division, said: “It represents a strong strategic fit, complementing Coreg CR, a leading treatment for heart failure and hypertension, and adds to our growing profile in the cardiovascular disease area.”

GSK was willing to pay a heavy premium to get its hands on Lovaza. Reliant had announced plans to float on the stock exchange, with an expected valuation of just $1.34 billion.

GSK has suffered in recent months after studies linked Avandia, its diabetes drug, to the risk of heart attack. Its shares have slumped 13 per cent since September.

Navid Malik, a Collins Stewart analyst, said that the deal was a surprisingly aggressive move from GSK, but that it offered strategic possibilities as well as driving sales.

The market for nonstatin Omega3 products, such as Lovaza, was worth $2.2 billion in 2006 and is growing at an estimated 20 per cent a year. Lovaza’s share is also increasing: sales soared 115 per cent in the nine months to September to reach $206 million.

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