US regulators have confirmed that Baxter’s recently withdrawn blood thinner heparin was contaminated with a chemically-modified form of chondroitin sulfate, a popular dietary supplement for joint pain derived from animals.

According to media reports, US Food and Drug Administration officials said during a conference call with journalists yesterday that it is likely that the substance found in the affected batches of heparin - over-sulfated chondroitin sulfate - was modified to mimic the actions of the drug, but stressed that its use has not been approved in medicines.

The agency is now trying to establish whether the contaminant, which is cheaper to manufacture than heparin, was added intentionally during production in China, and whether it is indeed responsible for the adverse events recorded in patients using the drug.

Last month Baxter was forced to temporarily suspend production of heparin at its plant in China following an increase in serious allergic reactions and low blood pressure in patients receiving high ‘bolus’ doses of the drug, including around 20 possible patient deaths.

Although it remains to be seen at which point in the production chain the contaminant was added to the drug, reports emerged earlier this year that the facility in China where heparin is made had not been inspected by US regulators.