Baxter Healthcare Corporation, which provides half the supply of heparin in the United States, recalled multidose vials of heparin sodium last month after four deaths and 350 reports of adverse events, 40% of which were serious.

More than one million multidose vials are sold each month in the US, and half of them are produced by Baxter, the US Food and Drug Administration said. The source of the heparin, which is made from pig intestines, was imported from China. The FDA said it had not inspected the Chinese plant that produced it.

The initial recall of heparin last month involved nine lots of multidose vials. Since then, Baxter has received reports of adverse reactions with other lots, the company said. Baxter and the FDA are investigating the problem.

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