American health officials have identified a contaminant in batches of a blood thinner that has been associated with 19 deaths in the U.S. and are trying to determine how the chemical got into the drug.

The lots of heparin were recalled Feb. 28, and Food and Drug Administration officials say no new deaths have been reported since then.

Heparin is derived from pig intestines, and China is the world's leading supplier.
(CBC)

Canada was not affected by the recall as the heparin sold here does not have the same ingredients, Health Canada officials said at the time.

The contaminant found in the U.S. version of heparin is oversulphated condroitin sulphate, according to Dr. Janet Woodcock, head of the FDA's Centre for Drug Evaluation and Research.

Condroitin sulphate is a natural compound that occurs widely and is used as a dietary supplement, but the oversulphated version has not been widely studied.

The investigation is continuing, Woodcock says, but officials are as yet unable to determine whether the contaminant was introduced accidentally or deliberately.

The lots of heparin linked to hundreds of allergic reactions, including dizziness, difficulty breathing, nausea and a racing heartbeat, were marketed by Baxter International and produced in China. The FDA said Chinese officials have been highly co-operative in the investigation.

Meanwhile, the FDA has initiated testing of heparin entering the U.S., and Woodcock said the agency feels "doctors and patients now can be confident that the product on the market has been tested and is safe."

Compound cheaper than heparin

Condroitin sulphate is a compound in the same family as heparin, so preliminary testing did not identify it, Woodcock said. She said more exacting tests by the government and university researchers uncovered the contaminant.

Oversulphated condroitin sulphate would be less expensive to make than heparin, but FDA officials said they could not estimate the cost difference.

The investigation comes just a year after melamine was identified as a contaminant in pet food from China. Officials said an agreement signed at that time with China helped smooth the way for the current investigation.

FDA officials said they could not yet directly link the oversulphated condroitin sulphate to the 19 U.S. deaths and numerous side-effects that occurred in people taking the drug, but it is the lone contaminant they have found in the product.

Heparin is derived from pig intestines, and China is the world's leading supplier. Tiny family-run workshops near slaughterhouses send batches of raw ingredients to larger middlemen before they reach factories.