Peter Dolan, the chief executive of Bristol-Myers Squibb, said yesterday that the earlier-than-expected start of generic competition to its flagship drug Plavix could threaten its entire clinical trials programme for the drug, and deny much-needed new information about the use of the drug to doctors and patients.

“While we are working hard to minimise the impact of this action on the company, we are concerned as well about the negative implications it will have for patients,” said Dolan in a letter to B-MS staff yesterday. “Bristol-Myers Squibb and Sanofi-Aventis have a long-term R&D plan for Plavix [clopidogrel] that cannot be sustained if we no longer have exclusivity for this product,” he warned.

Since 1997, he continued, more than 100,000 patients have participated in clinical trials involving Plavix that were developed and funded by B-MS and its partner Sanofi. Allowing early generic competition to products result in a negative environment for R&D in general - and ultimately hurt patients, said Dolan.

Canadian drugmaker Apotex went ahead and launched its generic clopidogrel product in the USA on Tuesday, despite B-MS and Sanofi-Aventis’ insistence that this contravenes patents held on the drug that extend out to 2012.

The three companies had earlier entered into a $40 million agreement in which Apotex agreed not to launch its generic version until 2011, but this was revoked by order of the state attorneys general last week for being unlawful. Ironically, in entering into the deal B-MS and Sanofi appear to have weakened their legal defence of Plavix in future litigation with Apotex, including reducing the damages the Canadian company will face should it lose the case.

Plavix had about $3.2n in US sales last year, and accounts for a third of the company's profits. It also contributes about 10% to 15% of the earnings of Sanofi, which sells it outsider the USA.

Apotex’ generic could also affect the fortunes of Eli Lilly and Daiichi Sankyo’s, which are developing a Plavix rival called prasugrel for acute coronary syndromes. Prasugrel is currently in a head-to-head trial against clopidogrel in this indication.