WASHINGTON (October 1, 2009)—The U.S. Food and Drug Administration is advising doctors that a widely used blood thinner has been reformulated to improve its safety, though the change could open the door to dosing errors.

The FDA says new heparin vials scheduled to ship next week will be 10 percent less potent than the original blood thinner.

The change is designed to make it easier to spot impurities in the drug.

Last year, contaminated heparin was linked to hundreds of life-threatening allergic reactions and more than 200 deaths.

Baxter International recalled the drug and the U.S. blocked imports from a Chinese company that supplied the key ingredient.

The FDA is warning doctors that extra heparin may now be required to treat some patients.