The U.S. Food and Drug Administration is investigating Baxter's version of the product, implicated in four deaths and 350 reports of allergic reactions this year.

In response, Baxter stopped making the blood thinner, which is used before kidney dialysis and heart surgeries.

To keep supplies in place, the FDA sent inspectors to China to inspect APP Pharmaceuticals' supplier and is acting to approve their new production lines, while the company positions itself to claim more of the heparin market, The Wall Street Journal reported.

The FDA said Wednesday it also was inspecting a Baxter plant in Cherry Hill, N.J., and a Scientific Protein Laboratories LLC plant in Waunakee, Wis., which supplies Baxter. A team will be sent to inspect their Chinese supplier, the FDA announced.

Major purchasers, such as Fresenius Medical Care AG, are making the switch to APP Pharmaceuticals' heparin. "We're no longer ordering Baxter heparin at this point," said Mark Moreau, senior director of materials management at Fresenius.

Before the crisis, Baxter and APP Pharmaceuticals each produced roughly half the nation's heparin supply.