VNU, the Dutch business information group, yesterday agreed to pay €5.8 billion in cash and stock - more than its market value - for IMS Health, a US company that gathers data on drug sales, but its shares fell amid fears it was overpaying.

The companies said they would create "a global leader in market intelligence", providing 12,000 clients - including Coca-Cola, Unilever and Procter & Gamble - in 110 countries with information on sales and the effectiveness of advertising, spanning consumer goods, media and healthcare markets.

Rob van den Bergh, VNU chief executive, who will head the combined company, said there was "compelling strategic logic" for the deal. The deal dwarfs the combined $5 billion (€4.14 billion) spent on two previous US purchases - Nielsen Media Ratings, a television ratings group, and AC Nielsen, which measures retail sales - in 1999 and 2000.

While investors fretted, sending VNU shares down 3.7 per cent at €22.49, analysts were upbeat. Stroeve, the Amsterdam stockbroker, said it was an "outstanding" strategic fit for VNU.

Rob Ruijter, VNU chief financial officer, said the deal would boost earnings per share in the first year and generate annual synergies of €110 million by 2008, requiring an outlay of €150 million ahead of that.

IMS shareholders will receive $11.25 a share in cash and 0.60415 VNU shares, equivalent to a 16 per cent premium to IMS's average price of the past 30 days. VNU shareholders will own 65 per cent of the combined group.