Boston Scientific says it has been given a "verbal assurance" by the US Food and Drug Administration (FDA) that there are no significant quality control problems at the company's heart stent manufacturing plant in Galway.

Spokesman Paul Sullivan told The Irish Times that the company was pleased with the Galway operation after the FDA sent a stern letter to the company's Massachusetts headquarters warning that it had very serious quality control problems across the company that could block it from getting new product approvals.

As Boston Scientific's share price dropped over two cents on Thursday as a result of the warning, company chairman Jim Tobin played up the FDA's approval of the Galway plant, the largest in the group, while admitting mistakes in the US.

"Although we are pleased with the result of the inspection of our largest plant, we have clearly not done enough to resolve the issues raised by the FDA last year.

"We are confident we have addressed many of the issues, but others have not yet been fully resolved," he said.

The FDA letter, sent to Boston Scientific's Massachusetts headquarters on Wednesday, warned of "serious regulatory problems" in medical devices produced at three US plants and said the company's previous efforts to deal with quality control problems at three other plants were inadequate. The letter warned that it could take action against Boston Scientific without further notice.

The letter arrived the same day that the company looked set to make its largest ever acquisition.

Indianapolis-based Guidant accepted a $27 billion (€22.3 billion) buyout bid from Boston Scientific, beating an offer by Johnson & Johnson.

The FDA's letter said that inspections conducted late last summer "revealed serious regulatory problems involving your medical devices".