Drugmaker Bristol-Myers Squibb Co has raised its offer for biotechnology firm ImClone Systems from the initial $60 a share to $62 a share, valuing the offer at around $4.7 billion.

Bristol-Myers raised its bid for ImClone to $62 after the biotechnology company rejected an earlier offer of $60 a share, saying it had received a higher, but still preliminary, $70 per-share takeover proposal from an unnamed pharmaceutical company.

Bristol-Myers said it plans to follow it up with second similar offer for all remaining ImClone shareholders. Bristol-Myers Squibb currently owns about 16.6 per cent in ImClone.

The latest offer to ImClone shareholders represents a 48 per cent premium to the average share price of ImClone stock during the three-month period ended 30 July, the last trading day prior to the initial offer.

''Bringing our offer directly to the company's stockholders allows them to evaluate the merits of our proposal and permits them a say in the future of their company, an approach I know you support,'' Bristol-Myers chairman and CEO James Cornelius said in a letter to Carl Icahn, chairman of ImClone.

Following the acquisition, Bristol-Myers proposes to seek ImClone shareholders' consent to remove all existing members of the company's board and replace them with five Bristol-Myers nominees.

Bristol-Myers already has a marketing alliance with ImClone for Erbitux, a drug indicated for the treatment of colon- and head-and-neck-cancer. Under the agreement, ImClone receives a 39 per cent royalty on net sales in North America. The agreement expires in September 2018.

ImClone has also tied up with German drugmaker Merck KgA, for Erbitux marketing in Europe.

Bristol-Myers and ImClone said clinical data showed a better survival rate for head and neck cancer patients after 5 years when adding Erbitux to chemotherapy.

Erbitux, which had global sales of $1.3 billion in 2007, has also received approval from Japanese drug authorities for treatment of patients with advanced or metastatic colorectal cancer.

Erbitux competes with Genentech's Avastin and Amgen's colon cancer drug Vectibix.

ImClone also has eight antibodies under preclinical testing for various forms of cancers.