The senior executive in charge of mergers and acquisitions at Bristol-Myers Squibb, the American pharmaceuticals giant that may be a takeover target for Sanofi-Aventis, its French rival, has left the company, The Times has learnt.

Tamar Howson, Bristol-Myers’s head of corporate and business development, is understood to have left at the end of last week, just days after unconfirmed reports that Bristol-Myers and Sanofi had reached a premerger agreement and would unveil a tie-up within weeks.

Ms Howson was the member of BMS’s management executive committee responsible for deals and licensing partnerships with other companies at the New York-based pharmaceuticals group.

A spokesman for the company confirmed that she had left “to pursue other interests”, but declined further comment on the reasons and timing of her departure.

Both companies continue to decline comment on the report.

Jean-François Dehecq, Sanofi’s chairman, said last week: “I am not ready to answer this question.”

However, Ms Howson’s sudden departure has fuelled concerns about a boardroom rift over the future direction of the troubled American drugs company, which last month reported that global sales had slipped 7 per cent to $17.9 billion (£9.1 billion) in 2006 from $19.2 billion in 2005.

Ms Howson joined Bristol-Myers in 2001 as a senior vice-president and oversaw a string of in-licensing agreements and research collaborations and partnerships.

In January, she helped to establish a collaboration with AstraZeneca, the British pharmaceuticals group, to develop and commercialise two drugs for the treatment of diabetes. She was formerly director of worldwide business development for SmithKline Beecham.

Ms Howson is the second senior executive to have left the company since September 12, when Peter Dolan, the chief executive, was forced out after a row over his mishandling of a patent dispute over Plavix, the group’s blood-thinning drug, which is BMS’s top-selling product, generating sales of $3.8 billion in 2005.

The incident allowed Apotex, a Canadian drug company, legally to flood the US market with a low-cost, generic version of Plavix, triggering a 62 per cent fall in sales of the branded drug in the fourth quarter of 2006 to $343 million from $906 million in the same period of 2005.

Mr Dolan was replaced by an interim chief executive, James Cornelius, a decision that has stoked speculation that the company may be up for sale.

Sanofi-Aventis, the world’s third-largest pharmaceutical company, collaborates with BMS on both Plavix and Avapro, which is a drug for hypertension.

A successful merger deal between Sanofi and BMS would create a pharmaceuticals giant with combined sales of $56 billion, which would be roughly the same size as Pfizer, the world No 1.

The combined market capitalisation of the two companies would be about $175 billion.

Conditions worsening

July 2006 US authorities launch a criminal investigation into Bristol-Myers Squibb after allegations that it paid off the Canadian drug maker Apotex not to produce a cheap version of its Plavix heart medicine

August 8 Apotex floods US market with generic Plavix after botched talks over patent rights governing the drug

August 21 US court halts distribution of generic Plavix

September 12 BMS chief executive Peter Dolan is ousted for his role in the affair. He is replaced by interim CEO James Cornelius. Speculation rife at a possible takeover of the group

December 8 A US court upholds the Plavix injunction, pending a full legal hearing on the patents governing the drug

December 22 BMS agrees to pay a $499 million (£253 million) settlement to stop investigations into the group’s drug-pricing and marketing practices

January 25, 2007 BMS reports 7 per cent slide in sales for 2006 due to loss of revenue from Plavix

January 29 Speculation grows about a possible takeover by French drugs giant Sanofi-Aventis

February Tamar Howson, BMS head of business development, steps down from the company

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