Baxter told the Wall Street Journal that the world's biggest drug firm had supplied the bulk active used to make the blood thinner at its manufacturing facility in Ohio.
Pfizer, which confirmed that it had supplied Baxter, told the paper that it sourced the ingredient from both the US and China but added that: “Baxter believes the lot used in Delaware used North American raw materials.”
The point of origin question is critical given the speculation that deaths linked to heparin over the last few years were the result of a reaction to oversulfated chondroitin sulfate (OSCS) that had been substituted for the genuine ingredient by unscrupulous suppliers in China.
Speaking last April, Food and Drug Administration (FDA) Commissioner Andrew von Eschenbach said the suspected the ingredient switch had been made "by virtue of economic fraud" adding that the replacement could only have been carried out deliberately.
FDA investigates latest deaths
A spokesman for Beebe Medical Center in Lewes confirmed the two deaths and said that a third patient, who had also been treated with the blood thinner, had also suffered medical problems.
He added that "We are not pointing fingers at Baxter. We don't know what's going on, but heparin is the only commonality that we were able to see ourselves."
The Associated Press reports that the deaths are under investigation by the FDA adding that samples, collected by an agency representative on Friday, have not been found to contain OSCS.
FDA spokeswoman Karen Riley said that the heparin samples have been sent to an agency laboratory in Cincinnati for more testing and added that: “at this point this appears to be an isolated incident."
While the FDA's investigation is well within its public health remit, the speed with which it has acted is no doubt a reaction to criticism it faced when problems with heparin emerged several years ago.