WASHINGTON, Feb. 13 (UPI) -- The supplier of half of a critical blood thinner in the United States has suspended production in the wake of potentially life-threatening allergic reactions.

Baxter International Inc. (NYSE:AX) stopped production of heparin due to reports of nausea, shortness of breath and a drop in blood pressure. More than 350 reports have been filed in 2008, the U.S. Food and Drug Administration reported.

Four deaths have been associated with heparin use but not under the circumstances that provoked the company's move. The FDA said the deaths didn't "follow the pattern" of the new concerns, the Chicago Tribune reported Wednesday.

The new concerns are associated with heavy, first-time doses -- known as "initial loading" -- prescribed before heart surgery or dialysis treatment. There are have been no problems reported with long-term use of heparin, the report said.

The 350 adverse reactions reported are more than triple the100 filed in 2007.

Baxter, however, makes 35 million vials a year, about half the nation's supply.

"There's going to be a shortage problem in the immediate and long-term future with the suspension of Baxter manufacturing," the director of the FDA's Office of New Drugs, Dr. John Jenkins, told the Tribune.